Tuesday, September 23, 2008
Early history of Windows
Early history: an expansion of MS-DOS
The first independent version of Microsoft Windows, version 1.0, released on 20 November 1985, lacked a degree of functionality and achieved little popularity. It was originally going to be called Interface Manager, but Rowland Hanson, the head of marketing at Microsoft, convinced the company that the name Windows would be more appealing to consumers. Windows 1.0 was not a complete operating system, but rather extended MS-DOS, and shared the latter's inherent flaws and problems. The first version of Microsoft Windows includes a simple graphics painting program called Windows Paint, Windows Write, a simple word processor, and also includes the MS-DOS Executive, an appointment calendar, a cardfiler, a notepad, a clock, a control panel, a terminal, Clipboard and RAM driver. It also includes a game called Reversi.
Furthermore, legal challenges by Apple limited its functionality. For example, windows can only appear "tiled" on the screen; that is, they cannot overlap or overlie one another. Also, there is no trash can (place to store files prior to deletion), since Apple claimed ownership of the rights to that paradigm. Microsoft later removed both of these limitations by signing a licensing agreement.
Microsoft Windows version 2 came out on 9 December 1987, and proved slightly more popular than its predecessor. Much of the popularity for Windows 2.0 came by way of its inclusion as a "run-time version" with Microsoft's new graphical applications, Excel and Word for Windows. They can be run from MS-DOS, executing Windows for the duration of their activity, and closing down Windows upon exit.
Microsoft Windows received a major boost around this time when Aldus PageMaker appeared in a Windows version, having previously run only on Macintosh. Some computer historians date this, the first appearance of a significant and non-Microsoft application for Windows, as the beginning of the success of Windows.
Versions 2.0x uses the real-mode memory model, which confines it to a maximum of 1 megabyte of memory. In such a configuration, it can run under another multitasker like DESQview, which use the 286 Protected Mode.
Later, two new versions were released: Windows/286 2.1 and Windows/386 2.1. Like previous versions of Windows, Windows/286 2.1 uses the real-mode memory model, but was the first version to support the HMA. Windows/386 2.1 has a protected mode kernel with LIM-standard EMS emulation, the predecessor to XMS which would finally change the topology of IBM PC computing. All Windows and DOS-based applications at the time were real mode, running over the protected mode kernel by using the virtual 8086 mode, which was new with the 80386 processor.
Version 2.03, and later 3.0, faced challenges from Apple over its overlapping windows and other features Apple charged mimicked the "look and feel" of its operating system and "embodie[d] and generate[d] a copy of the Macintosh" in its OS. Judge William Schwarzer dropped all but 10 of the 189 charges that Apple had sued Microsoft with on 5 January 1989.
Success with Windows 3.0:
Microsoft Windows scored a significant success with Windows 3.0, released in 1990. In addition to improved capabilities given to native applications, Windows also allows a user to better multitask older MS-DOS based software compared to Windows/386, thanks to the introduction of virtual memory. It made PC compatibles serious competitors to the Apple Macintosh. This benefited from the improved graphics available on PCs by this time (by means of VGA video cards), and the Protected/Enhanced mode which allowed Windows applications to use more memory in a more painless manner than their DOS counterparts could. Windows 3.0 can run in any of Real, Standard, or 386 Enhanced modes, and is compatible with any Intel processor from the 8086/8088 up to 80286 and 80386. Windows 3.0 tries to auto detect which mode to run in, although it can be forced to run in a specific mode using the switches: /r (real mode), /s ("standard" 286 protected mode) and /3 (386 enhanced protected mode) respectively. This was the first version to run Windows programs in protected mode, although the 386 enhanced mode kernel was an enhanced version of the protected mode kernel in Windows/386.
Due to this backward compatibility, Windows 3.0 applications also must be compiled in a 16-bit environment, without ever using the full 32-bit capabilities of the 386 CPU.
A "multimedia" version, Windows 3.0 with Multimedia Extensions 1.0, was released several months later. This was bundled with "multimedia upgrade kits", comprising a CD-ROM drive and a sound card, such as the Creative Labs Sound Blaster Pro. This version was the precursor to the multimedia features available in Windows 3.1 and later, and was part of the specification for Microsoft's specification for the Multimedia PC.
The features listed above and growing market support from application software developers made Windows 3.0 wildly successful, selling around 10 million copies in the two years before the release of version 3.1. Windows 3.0 became a major source of income for Microsoft, and led the company to revise some of its earlier plans.
OS/2:
During the mid to late 1980s, Microsoft and IBM had cooperatively been developing OS/2 as a successor to DOS. OS/2 would take full advantage of the aforementioned Protected Mode of the Intel 80286 processor and up to 16MB of memory. OS/2 1.0, released in 1987, supported swapping and multitasking and allowed running of DOS executables.
A GUI, called the Presentation Manager (PM), was not available with OS/2 until version 1.1, released in 1988. Its API was incompatible with Windows. (Among other things, Presentation Manager placed X,Y coordinate 0,0 at the bottom left of the screen like Cartesian coordinates, while Windows put 0,0 at the top left of the screen like most other computer window systems.) Version 1.2, released in 1989, introduced a new file system, HPFS, to replace the FAT file system.
By the early 1990s, conflicts developed in the Microsoft/IBM relationship. They cooperated with each other in developing their PC operating systems, and had access to each others' code. Microsoft wanted to further develop Windows, while IBM desired for future work to be based on OS/2. In an attempt to resolve this tension, IBM and Microsoft agreed that IBM would develop OS/2 2.0, to replace OS/2 1.3 and Windows 3.0, while Microsoft would develop a new operating system, OS/2 3.0, to later succeed OS/2 2.0.
This agreement soon however fell apart, and the Microsoft/IBM relationship was terminated. IBM continued to develop OS/2, while Microsoft changed the name of its (as yet unreleased) OS/2 3.0 to Windows NT. Both retained the rights to use OS/2 and Windows technology developed up to the termination of the agreement; Windows NT, however, was to be written anew, mostly independently (see below).
After an interim 1.3 version to fix up many remaining problems with the 1.x series, IBM released OS/2 version 2.0 in 1992. This was a major improvement: it featured a new, object-oriented GUI, the Workplace Shell (WPS), that included a desktop and was considered by many to be OS/2's best feature. Microsoft would later imitate much of it in Windows 95. Version 2.0 also provided a full 32-bit API, offered smooth multitasking and could take advantage of the 4 gigabytes of address space provided by the Intel 80386. Still, much of the system still had 16-bit code internally which required, among other things, device drivers to be 16-bit code as well. This was one of the reasons for the chronic shortage of OS/2 drivers for the latest devices. Version 2.0 could also run DOS and Windows 3.0 programs, since IBM had retained the right to use the DOS and Windows code as a result of the breakup.
Windows 3.1 and NT:
In response to the impending release of OS/2 2.0, Microsoft developed Windows 3.1, which includes several minor improvements to Windows 3.0 (such as display of TrueType scalable fonts, developed jointly with Apple), but primarily consists of bugfixes and multimedia support. It also excludes support for Real mode, and only runs on an 80286 or better processor. Later Microsoft also released Windows 3.11, a touch-up to Windows 3.1 which includes all of the patches and updates that followed the release of Windows 3.1 in 1992. Around the same time, Microsoft released Windows for Workgroups (WfW), available both as an add-on for existing Windows 3.1 installations and in a version that included the base Windows environment and the networking extensions all in one package. Windows for Workgroups includes improved network drivers and protocol stacks, and support for peer-to-peer networking. One optional download for WfW was the "Wolverine" TCP/IP protocol stack, which allowed for easy access to the Internet through corporate networks. There are two versions of Windows for Workgroups, WfW 3.1 and WfW 3.11. Unlike the previous versions, Windows for Workgroups 3.11 only runs in 386 Enhanced mode, and requires at least an 80386SX processor.
All these versions continued version 3.0's impressive sales pace. Even though the 3.1x series still lacked most of the important features of OS/2, such as long file names, a desktop, or protection of the system against misbehaving applications, Microsoft quickly took over the OS and GUI markets for the IBM PC. The Windows API became the de-facto standard for consumer software.
Meanwhile Microsoft continued to develop Windows NT. The main architect of the system was Dave Cutler, one of the chief architects of VMS at Digital Equipment Corporation (later purchased by Compaq, now part of Hewlett-Packard). Microsoft hired him in 1988 to create a portable version of OS/2, but Cutler created a completely new system instead. Cutler had been developing a follow-on to VMS at DEC called Mica, and when DEC dropped the project he brought the expertise and some engineers with him to Microsoft. DEC also believed he brought Mica's code to Microsoft and sued. Microsoft eventually paid $150 million U.S. and agreed to support DEC's Alpha CPU chip in NT.
Windows NT 3.1 (Microsoft marketing desired to make Windows NT appear to be a continuation of Windows 3.1) arrived in Beta form to developers at the July 1992 Professional Developers Conference in San Francisco. Microsoft announced at the conference its intentions to develop a successor to both Windows NT and Windows 3.1's replacement (code-named Chicago), which would unify the two into one operating system. This successor was codenamed Cairo. In hindsight, Cairo was a much more difficult project than Microsoft had anticipated, and as a result, NT and Chicago would not be unified until Windows XP, and still, parts of Cairo have not made it into Windows as of today. Specifically, the WinFS subsystem, which was the much touted Object File System of Cairo, which had been put on hold for a while, but Microsoft further announced that they have discontinued WinFS and will gradually incorporate the technologies developed for WinFS in other products and technologies, notably, Microsoft SQL Server.
Driver support was lacking due to the increased programming difficulty in dealing with NT's superior hardware abstraction model. This problem plagued the NT line all the way through Windows 2000. Programmers complained that it was too hard to write drivers for NT, and hardware developers were not going to go through the trouble of developing drivers for a small segment of the market. Additionally, although allowing for good performance and fuller exploitation of system resources, it was also resource-intensive on limited hardware, and thus was only suitable for larger, more expensive machines. Windows NT would not work for private users because of its resource demands; moreover, its GUI was simply a copy of Windows 3.1's, which was inferior to the OS/2 Workplace Shell, so there was not a good reason to propose it as a replacement to Windows 3.1.
However, the same features made Windows NT perfect for the LAN server market (which in 1993 was experiencing a rapid boom, as office networking was becoming a commodity), as it enjoyed advanced network connectivity options, and the efficient NTFS file system. Windows NT version 3.51 was Microsoft's stake into this market, a large part of which would be won over from Novell in the following years.
One of Microsoft's biggest advances initially developed for Windows NT was new 32-bit API, to replace the legacy 16-bit Windows API. This API was called Win32, and from then on Microsoft referred to the older 16-bit API as Win16. Win32 API had three main implementations: one for Windows NT, one for Win32s (which was a subset of Win32 which could be used on Windows 3.1 systems), and one for Chicago. Thus Microsoft sought to ensure some degree of compatibility between the Chicago design and Windows NT, even though the two systems had radically different internal architectures. Windows NT was the first Windows operating system based on a hybrid kernel.
Windows 95:
After Windows 3.11, Microsoft began to develop a new consumer oriented version of the operating system code-named Chicago. Chicago was designed to have support for 32-bit preemptive multitasking like OS/2 and Windows NT, although a 16-bit kernel would remain for the sake of backward compatibility. The Win32 API first introduced with Windows NT was adopted as the standard 32-bit programming interface, with Win16 compatibility being preserved through a technique known as "thunking". A new GUI was not originally planned as part of the release, although elements of the Cairo user interface were borrowed and added as other aspects of the release (notably Plug and Play) slipped.
Microsoft did not change all of the Windows code to 32-bit; parts of it remained 16-bit (albeit not directly using real mode) for reasons of compatibility, performance and development time. This, and the fact that the numerous design flaws had to be carried over from the earlier Windows versions, eventually began to impact on the operating system's efficiency and stability.
Microsoft marketing adopted Windows 95 as the product name for Chicago when it was released on 24 August 1995. Microsoft had a double gain from its release: first it made it impossible for consumers to run Windows 95 on a cheaper, non-Microsoft DOS; secondly, although traces of DOS were never completely removed from the system, and a version of DOS would be loaded briefly as a part of the booting process, Windows 95 applications ran solely in 386 Enhanced Mode, with a flat 32-bit address space and virtual memory. These features make it possible for Win32 applications to address up to 2 gigabytes of virtual RAM (with another 2GB reserved for the operating system), and in theory prevents them from inadvertently corrupting the memory space of other Win32 applications. In this respect the functionality of Windows 95 moved closer to Windows NT, although Windows 95/98/ME does not support more than 512 megabytes of physical RAM without obscure system tweaks.
IBM continued to market OS/2, producing later versions in OS/2 3.0 and 4.0 (also called Warp). Responding to complaints about OS/2 2.0's high demands on computer hardware, version 3.0 was significantly optimized both for speed and size. Before Windows 95 was released, OS/2 Warp 3.0 was even shipped preinstalled with several large German hardware vendor chains. However, with the release of Windows 95, OS/2 began to lose market share.
It is probably impossible to nail down a specific reason why OS/2 failed to gain much market share. While OS/2 continued to run Windows 3.1 applications, it lacked support for anything but the Win32s subset of Win32 API (see above). Unlike with Windows 3.1, IBM did not have access to the source code for Windows 95 and was unwilling to commit the time and resources to emulate the moving target of the Win32 API. IBM also introduced OS/2 into the United States v. Microsoft case, blaming unfair marketing tactics on Microsoft's part, but many people would probably agree that IBM's own marketing problems and lack of support for developers contributed at least as much to the failure.
Microsoft released five different versions of Windows 95:
- Windows 95 - original release
- Windows 95 A - included Windows 95 OSR1 slipstreamed into the installation.
- Windows 95 B - (OSR2) included several major enhancements, Internet Explorer (IE) 3.0 and full FAT32 file system support.
- Windows 95 B USB - (OSR2.1) included basic USB support.
- Windows 95 C - (OSR2.5) included all the above features, plus IE 4.0. This was the last 95 version produced.
OSR2, OSR2.1, and OSR2.5 were not released to the general public, rather, they were available only to OEMs that would preload the OS onto computers. Some companies sold new hard drives with OSR2 preinstalled (officially justifying this as needed due to the hard drive's capacity). This product was sold under the name Windows 97 in some countries in Europe.
The first Microsoft Plus! add-on pack was sold for Windows 95.
NT 4.0:
Microsoft released Windows NT 4.0, which features the new Windows 95 interface on top of the Windows NT kernel. (a patch was available for developers to make NT 3.51 use the new UI, but it was quite buggy).
Windows NT 4.0 came in four versions:
- Windows NT 4.0 Workstation
- Windows NT 4.0 Server
- Windows NT 4.0 Server, Enterprise Edition (includes support for 8-way SMP and clustering)
- Windows NT 4.0 Terminal Server
On 25 June 1998, Microsoft released Windows 98, which was widely regarded as a minor revision of Windows 95, but generally found to be more stable and reliable than its 1995 predecessor. It includes new hardware drivers and better support for the FAT32 file system which allows support for disk partitions larger than the 2 GB maximum accepted by Windows 95. The USB support in Windows 98 is far superior to the token, sketchy support provided by the OEM editions of Windows 95. It also controversially integrated the Internet Explorer browser into the Windows GUI and Windows Explorer file manager, prompting the opening of the United States v. Microsoft case, dealing with the question whether Microsoft was abusing its hold on the PC operating system market to unfairly compete with companies such as Netscape.
In 1999, Microsoft released Windows 98 Second Edition, an interim release whose most notable feature was the addition of Internet Connection Sharing, which was a form of network address translation, allowing several machines on a LAN (Local Area Network) to share a single Internet connection. Hardware support through device drivers was increased. Many minor problems present in the original Windows 98 were found and fixed which make it, according to many, the most stable release of Windows 9x.
Windows 2000:
Microsoft released Windows 2000, known during its development cycle as Windows NT 5.0, in February 2000. It was successfully deployed both on the server and the workstation markets. Amongst Windows 2000's most significant new features was Active Directory, a near-complete replacement of the NT 4.0 Windows Server domain model, which built on industry-standard technologies like DNS, LDAP, and Kerberos to connect machines to one another. Terminal Services, previously only available as a separate edition of NT 4, was expanded to all server versions. A number of features from Windows 98 were incorporated as well, such as an improved Device Manager, Windows Media Player, and a revised DirectX that made it possible for the first time for many modern games to work on the NT kernel. Windows 2000 is also the last NT-kernel Windows operating system to lack Product Activation.
While Windows 2000 upgrades were available for Windows 95 and Windows 98, it was not intended for home users.[1] It lacked device drivers for many common consumer devices such as scanners and printers[citation needed]. The original release of Windows 2000 had a buggy and counterintuitive installation procedure[citation needed]; this was not fully rectified until Service Pack 4 in June, 2003, after XP had been released.
Windows 2000 was available in six editions:
- Windows 2000 Professional
- Windows 2000 Server
- Windows 2000 Advanced Server
- Windows 2000 Datacenter Server
- Windows 2000 Advanced Server Limited Edition
- Windows 2000 Datacenter Server Limited Edition
WindowsMillenniumEdition(Me):
In September 2000, Microsoft introduced Windows Me (Millennium Edition), which upgraded Windows 98 with enhanced multimedia and Internet features. It also introduced the first version of System Restore, which allowed users to revert their system state to a previous "known-good" point in the case of system failure. System Restore was a notable feature that made its way into Windows XP. The first version of Windows Movie Maker was introduced as well.
Windows Me was conceived as a quick one-year project that served as a stopgap release between Windows 98 and Windows XP. Many of the new features were available from the Windows Update site as updates for older Windows versions, (System Restore was an exception). As a result, Windows Me was not acknowledged as a unique Operating System along the lines of 95 or 98. Windows Me was widely criticised for serious stability issues, and for lacking real mode DOS support, to the point of being referred to as the "Mistake Edition". Windows Me was the last operating system to be based on the Windows 9x (monolithic) kernel and MS-DOS. It is also the last 32-bit release of Microsoft Windows that did not include Product Activation.
Windows XP:
In 2001, Microsoft introduced Windows XP (codenamed "Whistler"). The merging of the Windows NT/2000 and Windows 95/98/Me lines was finally achieved with Windows XP. Windows XP uses the Windows NT 5.1 kernel, marking the entrance of the Windows NT core to the consumer market, to replace the aging 16/32-bit branch. The initial release met with considerable criticism, particularly in the area of security, leading to the release of three major Service Packs. Windows XP SP1 was released in September of 2002, SP2 came out in August, 2004 and SP3 came out in April, 2008. Service Pack 2 provided significant improvements and encouraged widespread adoption of XP among both home and business users. Windows XP was the current edition longer than any other version of Windows, from 2001 all the way to 2007 when Windows Vista was released to consumers. The Windows XP line of operating systems was succeeded by Windows Vista on 30 January 2007.
Windows XP is available in a number of versions:
- "Windows XP Home Edition", for home desktops and laptops (notebooks)
- "Windows XP Home Edition N", as above, but without a default installation of Windows Media Player, as mandated by a European Union ruling
- "Windows XP Professional", for business and power users
- "Windows XP Professional N", as above, but without a default installation of Windows Media Player, as mandated by a European Union ruling
- Windows XP Media Center Edition (MCE), released in November 2002 for desktops and notebooks with an emphasis on home entertainment
- Windows XP Media Center Edition 2003
- Windows XP Media Center Edition 2004
- Windows XP Media Center Edition 2005, released on 12 October 2004.
- "Windows XP Tablet PC Edition", for tablet PCs (PCs with touch screens)
- Windows XP Tablet PC Edition 2005
- Windows XP Embedded, for embedded systems
- "Windows XP Starter Edition", for new computer users in developing countries
- Windows XP Professional x64 Edition, released on 25 April 2005 for home and workstation systems utilizing 64-bit processors based on the x86-64 instruction set developed by AMD as AMD64; Intel calls their version Intel 64)
- Windows XP 64-bit Edition, is a version for Intel's Itanium line of processors; maintains 32-bit compatibility solely through a software emulator. It is roughly analogous to Windows XP Professional in features. It was discontinued in September 2005 when the last vendor of Itanium workstations stopped shipping Itanium systems marketed as "Workstations".
- Windows XP 64-bit Edition 2003, based on the Windows NT 5.2 codebase.
WindowsServer2003:
On 24 April 2003 Microsoft launched Windows Server 2003, a notable update to Windows 2000 Server encompassing many new security features, a new "Manage Your Server" wizard that simplifies configuring a machine for specific roles, and improved performance. It has the version number NT 5.2. A few services not essential for server environments are disabled by default for stability reasons, most noticeable are the "Windows Audio" and "Themes" services; Users have to enable them manually to get sound or the "Luna" look as per Windows XP. The hardware acceleration for display is also turned off by default, users have to turn the acceleration level up themselves if they trust the display card driver.
In December 2005, Microsoft released Windows Server 2003 R2, which is actually Windows Server 2003 with SP1 (Service Pack 1) plus an add-on package. Among the new features are a number of management features for branch offices, file serving, printing and company-wide identity integration.
Windows Server 2003 is available in six editions:
- Web Edition (32-bit)
- Standard Edition (32 and 64-bit)
- Enterprise Edition (32 and 64-bit)
- Datacenter Edition (64-bit)
- Small Business Server (32-bit)
- Storage Server (OEM channel only)
WindowsVista:
The current client version of Windows, Windows Vista (codenamed Longhorn) was released on 30 November 2006[1] to business customers, with consumer versions following on 30 January 2007. Windows Vista intends to have enhanced security by introducing a new restricted user mode called User Account Control, replacing the "administrator-by-default" philosophy of Windows XP. Vista also features new graphics features, the Windows Aero GUI, new applications (such as Windows Calendar, Windows DVD Maker and some new games including Chess, Mahjong, and Purble Place), a revised and more secure version of Internet Explorer, a new version of Windows Media Player, and a large number of underlying architectural changes.
Windows Vista ships in several editions:
- Starter (only available in developing countries)
- Home Basic
- Home Premium
- Business
- Enterprise (only available to large businesses and enterprises)
- Ultimate (combines both Home Premium and Enterprise)
All editions (except Starter edition) are available in both 32-bit and 64-bit versions. The biggest advantage of the 64-bit version is breaking the 4 gigabyte memory barrier, which 32-bit computers cannot fully access. In the first year after Vista's release, most installations were still 32-bit, due to poor driver support of the 64-bit version.
WindowsServer:2008
Windows Server 2008, released on 27 February 2008, was originally known as Windows Server Codename "Longhorn". Windows Server 2008 builds on the technological and security advances first introduced with Windows Vista, and is significantly more modular than its predecessor, Windows Server 2003.
Google Earth
| Google Earth | |
|---|---|
 | |
 Screenshot of Google Earth in Windows Vista | |
| Developed by | |
| Initial release | mid 2006 |
| Latest release | 4.3.7284.3916 / 2008-07-13 |
| OS | Windows 2000, XP & Vista, Mac OS X, Linux |
| Size | 25MB |
| Available in | English, Turkish, Swahili, German, Dutch, French, Spanish, Italian, Japanese and Traditional Chinese |
| Type | Virtual globe |
| License | Freeware/Proprietary |
| Website | http://earth.google.com/ |
Google Earth is a proprietary virtual globe program that was originally called Earth Viewer, and was created by Keyhole, Inc, a company acquired by Google in 2004. It maps the earth by the superimposition of images obtained from satellite imagery, aerial photography and GIS 3D globe. It is available under three different licenses: Google Earth, a free version with limited functionality; Google Earth Plus ($20 per year), which includes additional features; and Google Earth Pro ($400 per year), which is intended for commercial use.[1]
The product, renamed Google Earth in 2006, is currently available for use on personal computers running Microsoft Windows 2000, XP, or Vista, Mac OS X 10.3.9 and above, Linux (released on June 12, 2006), and FreeBSD. Google Earth is also available as a browser plugin (released on June 2, 2008) for Firefox, IE6, or IE7. In addition to releasing an updated Keyhole based client, Google also added the imagery from the Earth database to their web based mapping software. The release of Google Earth in mid 2006 to the public caused a more than tenfold increase in media coverage on virtual globes between 2006 and 2007,[2] driving public interest in geospatial technologies and applications.
Google Earth
BSNL(Bharat Sanchar Nigam Limited)
 | |
| Type | Communication Service Provider |
|---|---|
| Availability | Countrywide except Delhi & Mumbai |
| Founded | 19th century, incorporated 2000 |
| Revenue | US$ 9.67 billion (2007) |
| Owner | The Government of India |
| Key people | Kuldeep Goyal(CMD), Praveen S[JTO] |
| Website www.bsnl.in www.bsnl.co.in | |
Bharat Sanchar Nigam Limited (known as BSNL, India Communications Corporation Limited) is a public sector communications company in India. It is the India's largest telecommunication company with 24% market share as on March 31, 2008. Its headquarters are at Bharat Sanchar Bhawan, Harish Chandra Mathur Lane, Janpath, New Delhi. It has the status of Mini-ratna - a status assigned to reputed Public Sector companies in India.
BSNL is India's oldest and largest Communication Service Provider (CSP). Currently has a customer base of 73 million as of June 2008.[1] It has footprints throughout India except for the metropolitan cities of Mumbai and New Delhi which are managed by MTNL. As on March 31, 2008 BSNL commanded a customer base of 31.55 million Wireline, 4.58 million CDMA-WLL and 36.21 million GSM Mobile subscribers. BSNL's earnings for the Financial Year ending March 31, 2007 stood at INR 397.15b (US$ 9.67 b) with net profit of INR 78.06b (US$ 1.90 billion). Today, BSNL is India's largest Telco and one of the largest Public Sector Undertaking with estimated market value of $ 100 Billion. The company is planning an IPO with in 6 months to offload 10% to public in the Rs 300-400 range valuing the company at over $100 billion.
Monday, September 22, 2008
Resistor
A resistor is a two-terminal electronic component designed to oppose an electric current by producing a voltage drop between its terminals in proportion to the current, that is, in accordance with Ohm's law: V = IR. The resistance R is equal to the voltage drop V across the resistor divided by the current I through the resistor.
Resistors are characterized primarily by their resistance and the power they can dissipate. Other characteristics include temperature coefficient, noise, and inductance. Practical resistors can be made of resistive wire, and various compounds and films, and they can be integrated into hybrid and printed circuits. Size, and position of leads are relevant to equipment designers; resistors must be physically large enough not to overheat when dissipating their power. Variable resistors, adjustable by changing the position of a tapping on the resistive element, and resistors with a movable tap ("potentiometers"), either adjustable by the user of equipment or contained within, are also used.
Resistors are used as part of electrical networks and electronic circuits.
There are special types of resistor whose resistance varies with various quantities, most of which have names, and articles, of their own: the resistance of thermistors varies greatly with temperature, whether external or due to dissipation, so they can be used for temperature or current sensing; metal oxide varistors drop to a very low resistance when a high voltage is applied, making them suitable for over-voltage protection; the resistance of a strain gauge varies with mechanical load; the resistance of photoresistors varies with illumination; the resistance of a Quantum Tunnelling Composite can vary by a factor of 1012 with mechanical pressure applied; and so on.
 | ||
| Potentiometer | ||
 |  | |
| Resistor | Variable Resistor |
 | ||
| Potentiometer | ||
 |  | |
| Resistor | Variable resistor |
Production resistors
There are various standards specifying properties of resistors for use in equipment:
- BS 1852
- EIA-RS-279
- MIL-PRF-26
- MIL-PRF-39007
- MIL-PRF-55342
- MIL-PRF-914
- MIL-R-11
- MIL-R-39008
- MIL-R-39017
There are other United States military procurement MIL-R- standards.
Four-band axial resistors
Four-band identification is the most commonly used color-coding scheme on all resistors. It consists of four colored bands that are painted around the body of the resistor. The first two bands encode the first two significant digits of the resistance value, the third is a power-of-ten multiplier or number-of-zeroes, and the fourth is the tolerance accuracy, or acceptable error, of the value. Sometimes a fifth band identifies the thermal coefficient, but this must be distinguished from the true 5-color system, with 3 significant digits.
For example, green-blue-yellow-red is 56×104 Ω = 560 kΩ ± 2%. An easier description can be as followed: the first band, green, has a value of 5 and the second band, blue, has a value of 6, and is counted as 56. The third band, yellow, has a value of 104, which adds four 0's to the end, creating 560,000Ω at ±2% tolerance accuracy. 560,000Ω changes to 560 kΩ ±2% (as a kilo- is 103).
Each color corresponds to a certain digit, progressing from darker to lighter colors, as shown in the chart below.
| Color | 1st band | 2nd band | 3rd band (multiplier) | 4th band (tolerance) | Temp. Coefficient |
|---|---|---|---|---|---|
| Black | 0 | 0 | ×100 | ||
| Brown | 1 | 1 | ×101 | ±1% (F) | 100 ppm |
| Red | 2 | 2 | ×102 | ±2% (G) | 50 ppm |
| Orange | 3 | 3 | ×103 | 15 ppm | |
| Yellow | 4 | 4 | ×104 | 25 ppm | |
| Green | 5 | 5 | ×105 | ±0.5% (D) | |
| Blue | 6 | 6 | ×106 | ±0.25% (C) | |
| Violet | 7 | 7 | ×107 | ±0.1% (B) | |
| Gray | 8 | 8 | ×108 | ±0.05% (A) | |
| White | 9 | 9 | ×109 | ||
| Gold | ×10-1 | ±5% (J) | |||
| Silver | ×10-2 | ±10% (K) | |||
| None | ±20% (M) |
SMT resistors
Surface mounted resistors are printed with numerical values in a code related to that used on axial resistors. Standard-tolerance Surface Mount Technology (SMT) resistors are marked with a three-digit code, in which the first two digits are the first two significant digits of the value and the third digit is the power of ten (the number of zeroes). For example:
| "334" | = 33 × 10,000 ohms = 330 kilohms |
| "222" | = 22 × 100 ohms = 2.2 kilohms |
| "473" | = 47 × 1,000 ohms = 47 kilohms |
| "105" | = 10 × 100,000 ohms = 1 megohm |
Resistances less than 100 ohms are written: 100, 220, 470. The final zero represents ten to the power zero, which is 1. For example:
| "100" | = 10 × 1 ohm = 10 ohms |
| "220" | = 22 × 1 ohm = 22 ohms |
Sometimes these values are marked as "10" or "22" to prevent a mistake.
Resistances less than 10 ohms have 'R' to indicate the position of the decimal point (radix point). For example:
| "4R7" | = 4.7 ohms |
| "0R22" | = 0.22 ohms |
| "0R01" | = 0.01 ohms |
Precision resistors are marked with a four-digit code, in which the first three digits are the significant figures and the fourth is the power of ten. For example:
| "1001" | = 100 × 10 ohms = 1 kilohm |
| "4992" | = 499 × 100 ohms = 49.9 kilohm |
| "1000" | = 100 × 1 ohm = 100 ohms |
"000" and "0000" sometimes appear as values on surface-mount zero-ohm links, since these have (approximately) zero resistance.
Cricket
Cricket is a bat-and-ball team sport that originated in England and is now played in more than 100 countries. A cricket match is contested by two teams, usually of eleven players each [1].
A cricket match is played on a grass field in the centre of which is a flat strip of ground 22 yards (20 m) long called a cricket pitch. A wicket, usually made of wood, is placed at each end of the pitch and used as a target.
The bowler, a player from the fielding team, bowls a hard leather, fist-sized, 5.5 ounces (160 g) cricket ball from the vicinity of one wicket towards the other, which is guarded by the batsman, a player from the opposing team. The ball usually bounces once before reaching the batsman. In defence of his wicket, the batsman plays the ball with a wooden cricket bat. Meanwhile, the other members of the bowler's team stand in various positions around the field as fielders, players who retrieve the ball in an effort to stop the batsman scoring runs, and if possible to get him or her out. The batsman — if he or she does not get out — may run between the wickets, exchanging ends with a second batsman (the "non-striker"), who has been stationed at the other end of the pitch. Each completed exchange of ends scores one run. Runs are also scored if the batsman hits the ball to the boundary of the playing area. The match is won by the team that scores more runs.
Cricket is essentially an outdoor sport, certainly at major level, and some games are played under floodlights. It cannot be played in poor weather due to the risk of accidents and so it is a seasonal sport. For example, it is played during the summer months in Great Britain, Australia, New Zealand and South Africa, while in the West Indies, India, Pakistan, Sri Lanka and Bangladesh it is played mostly during the winter months to escape the hurricane and monsoon seasons.
Governance rests primarily with the International Cricket Council (ICC), based in Dubai, which organises the sport worldwide via the domestic controlling bodies of the member countries. The ICC administers both men's and women's cricket, both versions being played at international level. Although men cannot play women's cricket, the rules do not disqualify women from playing in a men's team.
The rules are in the form of a code known as The Laws of Cricket [2] and these are maintained by the Marylebone Cricket Club (MCC), based in London, in consultation with the ICC and the domestic boards of control.
The game of cricket and its objectives
A cricket match is played between two teams (or sides) of eleven players each on a field of variable size and shape. The ground is grassy and is prepared by groundsmen whose jobs include fertilising, mowing, rolling and leveling the surface. Field diameters of 140–160 yards (130–150 m) are usual. The perimeter of the field is known as the boundary and this is sometimes painted and sometimes marked by a rope that encircles the outer edge of the field. The field may be round, square or oval – one of cricket's most famous venues is called The Oval.
In simple terms, the object of each team is to score more "runs" than the other team and so win the game. However, in certain types of cricket, it is also necessary to completely "dismiss" the other team in order to win the match which would otherwise be drawn.
Before play commences, the two team captains toss a coin to decide which team shall bat or bowl first. The captain who wins the toss makes his decision on the basis of tactical considerations which may include the current and expected pitch and weather conditions.
The key action takes place in a specially prepared area of the field (generally in the centre) that is called the "pitch". At either end of the pitch, 22 yards (20 m) apart, are placed the "wickets". These serve as a target for the "bowling" aka "fielding" side and are defended by the "batting" side which seeks to accumulate runs. Basically, a run is scored when the "batsman" has literally run the length of the pitch after hitting the ball with his bat, although as explained below there are many ways of scoring runs [3]. If the batsmen are not attempting to score any more runs, the ball is "dead" and is returned to the bowler to be bowled again [4].
The bowling side seeks to dismiss the batsmen by various means [5] until the batting side is "all out", whereupon the side that was bowling takes its turn to bat and the side that was batting must "take the field" [6].
In normal circumstances, there are 15 people on the field while a match is in play. Two of these are the "umpires" who regulate all on-field activity. Two are the batsmen, one of whom is the "striker" as he is facing the bowling; the other is called the "non-striker". The roles of the batsmen are interchangeable as runs are scored and "overs" are completed. The fielding side has all 11 players on the field together. One of them is the "bowler", another is the "wicketkeeper" and the other nine are called "fielders". The wicketkeeper (or keeper) is nearly always a specialist but any of the fielders can be called upon to bowl.
Pitch, wickets and creases
The pitch is 22 yards (20 m) long [7] between the wickets and is 10 feet (3.0 m) wide. It is a flat surface and has very short grass that tends to be worn away as the game progresses. The "condition" of the pitch has a significant bearing on the match and team tactics are always determined with the state of the pitch, both current and anticipated, as a deciding factor.
Each wicket consists of three wooden stumps placed in a straight line and surmounted by two wooden crosspieces called bails; the total height of the wicket including bails is 28.5 inches (720 mm) and the combined width of the three stumps is 9 inches (230 mm).
Four lines (aka creases) are painted onto the pitch around the wicket areas to define the batsman's "safe territory" and to determine the limit of the bowler's approach. These are called the "popping" (or batting) crease, the bowling crease and two "return" creases.
The stumps are placed in line on the bowling creases and so these must be 22 yards (20 m) apart. A bowling crease is 8 feet 8 inches (2.6 m) long with the middle stump placed dead centre. The popping crease has the same length, is parallel to the bowling crease and is 4 feet (1.2 m) in front of the wicket. The return creases are perpendicular to the other two; they are adjoined to the ends of the popping crease and are drawn through the ends of the bowling crease to a length of at least 8 feet (2.4 m).
When bowling the ball, the bowler's back foot in his "delivery stride" must land within the two return creases while his front foot must land on or behind the popping crease. If he breaks this rule, the umpire calls "No ball".
The batsman uses the popping crease at his end to stand when facing the bowler but it is more important to him that because it marks the limit of his safe territory and he can be stumped or run out (see Dismissals below) if the wicket is broken while he is "out of his ground".
Pitches vary in consistency, and thus in the amount of bounce, spin, and seam movement available to the bowler. Hard pitches are usually good to bat on because of high but even bounce. Dry pitches tend to deteriorate for batting as cracks often appear, and when this happens spinners can play a major role. Damp pitches, or pitches covered in grass (termed "green" pitches), allow good fast bowlers to extract extra bounce and seam movement. Such pitches tend to offer help to fast bowlers throughout the match, but become better for batting as the game goes on.
Bat and ball
The essence of the sport is that a bowler delivers the ball from his end of the pitch towards the batsman who, armed with a bat is "on strike" at the other end.
The bat is made of wood and takes the shape of a blade topped by a cylindrical handle. The blade must not be more than 4.25 inches (108 mm) wide and the total length of the bat not more than 38 inches (970 mm).
The bowler must employ an action in which the elbow does not straighten (within certain tolerance levels) to "bowl" the ball, which is a hard leather seamed spheroid projectile with a circumference limit of 9 inches (230 mm).
The hardness of the ball, which can be delivered at speeds of more than 90 miles per hour (140 km/h), is a matter for concern and batsmen wear protective clothing including "pads" (designed to protect the knees and shins), "batting gloves" for the hands, a helmet for the head and a "box" inside the trousers (for the more delicate part of the anatomy). Some batsmen wear additional padding inside their shirts and trousers such as thigh pads, arm pads, rib protectors and shoulder pads.
Umpires and scorers
The game on the field is regulated by two umpires, one of whom stands behind the wicket at the bowler's end, the other in a position called "square leg" which is several yards behind the batsman on strike. When the bowler delivers the ball, the umpire at the wicket is between the bowler and the non-striker. The umpires confer if there is doubt about playing conditions and can postpone the match by taking the players off the field if necessary: e.g., rain, deterioration of the light, crowd trouble.
Off the field and in televised matches, there is often a third umpire who can make decisions on certain incidents with the aid of video evidence. The third umpire is mandatory under the playing conditions for Test matches and limited overs internationals played between two ICC full members. These matches also have a match referee whose job is to ensure that play is within the Laws of cricket and the spirit of the game.
Off the field, the match details including runs and dismissals are recorded by two official scorers, one representing each team. The scorers are directed by the hand signals of an umpire. For example, the umpire raises a forefinger to signal that the batsman is out (has been dismissed); he raises both arms above his head if the batsman has hit the ball for six runs. The scorers are required by the Laws of cricket to record all runs scored, wickets taken and overs bowled. In practice they accumulate much additional data such as bowling analyses and run rates.
Unofficial scoring is carried on by spectators for their own benefit and by media scorers on behalf of broadcasters and newspapers.
Innings
The innings (always used in the plural form) is the term used for the collective performance of the batting side [8]. In theory, all eleven members of the batting side take a turn to bat but, for various reasons, an "innings" can end before they all do so (see below).
Depending on the type of match being played, each team has one or two innings apiece. The term "innings" is also sometimes used to describe an individual batsman's contribution ("he played a fine innings" etc).
The main aim of the bowler, supported by his fielders, is to dismiss the batsman. A batsman when dismissed is said to be "out" and that means he must leave the field of play and be replaced by the next batsman on his team. When ten batsmen have been dismissed (i.e., are out), then the whole team is dismissed and the innings is over. The last batsman, the one who has not been dismissed, is not allowed to continue alone as there must always be two batsmen "in". This batsman is termed "not out".
If an innings should end before ten batsmen have been dismissed, there are two "not out" batsmen. An innings can end early because the batting side's captain has chosen to "declare" the innings closed, which is a tactical decision; or because the batting side has achieved its target and won the game; or because the game has ended prematurely due to bad weather or running out of time. In limited overs cricket, there might be two batsmen still "in" when the last of the allotted overs has been bowled.
Overs
The bowler bowls the ball in sets of six deliveries (or "balls") and each set of six balls is called an over. This name came about because the umpire calls "Over!" when six balls have been bowled. At this point, another bowler is deployed at the other end and the fielding side changes ends. A bowler cannot bowl two successive overs, although a bowler can bowl unchanged at the same end for several overs. The batsmen do not change ends and so the one who was non-striker is now the striker and vice-versa. The umpires also change positions so that the one who was at square leg now stands behind the wicket at the non-striker's end and vice-versa.
Team structure
A team consists of eleven players. Depending on his or her primary skills, a player may be classified as a specialist batsman or bowler. A well-balanced team usually has five or six specialist batsmen and four or five specialist bowlers. Teams nearly always include a specialist wicket-keeper because of the importance of this fielding position. Each team is headed by a captain who is responsible for making tactical decisions such as determining the batting order, the placement of fielders and the rotation of bowlers.
A player who excels in both batting and bowling is known as an all-rounder. One who excels as a batsman and wicket-keeper is known as a "wicket-keeper/batsman", sometimes regarded as a type of all-rounder. True all-rounders are rare as most players focus on either batting or bowling skills.
Fielding
All eleven players on the fielding side take the field together.
One of them is the wicket-keeper aka "keeper" who operates behind the wicket being defended by the batsman on strike. Wicket-keeping is normally a specialist occupation and his primary job is to gather deliveries that the batsman does not hit, so that the batsmen cannot run byes. He wears special gloves (he is the only fielder allowed to do so), and pads to cover his lower legs. Owing to his position directly behind the striker, the wicket-keeper has a good chance of getting a batsman out caught off a fine edge from the bat. He is the only player who can get a batsman out stumped.
Apart from the one currently bowling, the other nine fielders are tactically deployed by the team captain in chosen positions around the field. These positions are not fixed but they are known by specific and sometimes colourful names such as "slip", "third man", "silly mid on" and "long leg". There are always many unprotected areas.
The captain is the most important member of the fielding side as he determines all the tactics including who should bowl (and how); and he is responsible for "setting the field", though usually in consultation with the bowler.
In all forms of cricket, if a fielder gets injured or becomes ill during a match, a substitute is allowed to field instead of him. The substitute cannot bowl, act as a captain or keep wicket. The substitute leaves the field when the injured player is fit to return.
Bowling
The bowler reaches his delivery stride by means of a "run-up", although some bowlers with a very slow delivery take no more than a couple of steps before bowling. A fast bowler needs momentum and takes quite a long run-up, running very fast as he does so.
The fastest bowlers can deliver the ball at a speed of over 90 miles per hour (140 km/h) and they sometimes rely on sheer speed to try and defeat the batsman, who is forced to react very quickly to a ball that reaches him in an instant.
Other fast bowlers rely on a mixture of speed and guile. Some fast bowlers make use of the seam of the ball so that it "curves" or "swings" in flight and this type of delivery can deceive a batsman into mistiming his shot so that the ball touches the edge of the bat and can then be "caught behind" by the wicketkeeper or a slip fielder.
At the other end of the bowling scale is the "spinner" who bowls at a relatively slow pace and relies entirely on guile to deceive the batsman. A spinner will often "buy his wicket" by "tossing one up" to lure the batsman into making an adventurous shot. The batsman has to be very wary of such deliveries as they are often "flighted" or spun so that the ball will not behave quite as he expects and he could be "trapped" into getting himself out.
In between the pacemen and the spinners are the "medium pacers" who rely on persistent accuracy to try and contain the rate of scoring and wear down the batsman's concentration.
All bowlers are classified according to their pace or style. The classifications, as with much cricket terminology, can be very confusing. Hence, a bowler could be classified as LF, meaning he is a left arm fast bowler; or as LBG, meaning he is a right arm spin bowler who bowls deliveries that are called a "leg break" and a "googly"!
During the bowling action the elbow may be held at any angle and may bend further, but may not straighten out. If the elbow straightens illegally then the square-leg umpire may call no-ball. The current laws allow a bowler to straighten his arm 15 degrees or less.
Batting
At any one time, there are two batsmen in the playing area. One takes station at the striker's end to defend the wicket as above and to score runs if possible. His partner, the non-striker, is at the end where the bowler is operating.
Batsmen come in to bat in a batting order, decided by the team captain. The first two batsmen - the "openers" - usually face the most hostile bowling, from fresh fast bowlers with a new ball. The top batting positions are usually given to the most competent batsmen in the team, and the non-batsmen typically bat last. The pre-announced batting order is not mandatory and when a wicket falls any player who has not yet batted may be sent in next.
If a batsman "retires" (usually due to injury) and cannot return, he is actually "not out" and his retirement does not count as a dismissal, though in effect he has been dismissed because his innings is over. Substitute batsmen are not allowed, although substitute fielders are.
A skilled batsman can use a wide array of "shots" or "strokes" in both defensive and attacking mode. The idea is to hit the ball to best effect with the flat surface of the bat's blade. If the ball touches the side of the bat it is called an "edge". Batsmen do not always seek to hit the ball as hard as possible and a good player can score runs just by making a deft stroke with a turn of the wrists or by simply "blocking" the ball but directing it away from fielders so that he has time to take a run.
There is a wide variety of shots played in cricket. The batsman's repertoire includes strokes named according to the style of swing and the direction aimed: e.g., "cut", "drive", "hook", "pull", etc.
Note that a batsman does not have to play a shot and can "leave" the ball to go through to the wicketkeeper, providing he thinks it will not hit his wicket. Equally, he does not have to attempt a run when he hits the ball with his bat. He can deliberately use his leg to block the ball and thereby "pad it away" but this is risky because of the lbw rule.
In the event of an injured batsman being fit to bat but not to run, the umpires and the fielding captain may allow another member of the batting side to be a runner. If possible, the runner must already have batted. The runner's only task is to run between the wickets instead of the injured batsman. The runner is required to wear and carry exactly the same equipment as the incapacitated batsman. It is possible for both batsmen to have runners.
Runs
The primary concern of the batsman on strike (i.e., the "striker") is to prevent the ball hitting the wicket and secondarily to score runs by hitting the ball with his bat so that he and his partner have time to run from one end of the pitch to the other before the fielding side can return the ball. To register a run, both runners must touch the ground behind the crease with either their bats or their bodies (the batsmen carry their bats as they run). Each completed run increments the score.
More than one run can be scored from a single hit but, while hits worth one to three runs are common, the size of the field is such that it is usually difficult to run four or more. To compensate for this, hits that reach the boundary of the field are automatically awarded four runs if the ball touches the ground en route to the boundary or six runs if the ball clears the boundary on the full. The batsmen do not need to run if the ball reaches or crosses the boundary.
Hits for five are unusual and generally rely on the help of "overthrows" by a fielder returning the ball. If an odd number of runs is scored by the striker, the two batsmen have changed ends and the one who was non-striker is now the striker. Only the striker can score individual runs but all runs are added to the team's total.
The decision to attempt a run is ideally made by the batsman who has the better view of the ball's progress and this is communicated by calling: "yes", "no" and "wait" are often heard.
Running is a calculated risk because if a fielder breaks the wicket with the ball while no part of the batsman or his bat is grounded behind the popping crease, the batsman nearest the broken wicket is run out.
A team's score is reported in terms of the number of runs scored and the number of batsmen that have been dismissed. For example, if five batsmen are out and the team has scored 224 runs, they are said to have scored 224 for the loss of 5 wickets (commonly shortened to "224 for five" and written 224/5 or, in Australia, "five for 224" and 5/224).
Extras
Additional runs can be gained by the batting team as extras (called "sundries" in Australia) by courtesy of the fielding side. This is achieved in four ways:
- No ball – a penalty of one extra that is conceded by the bowler if he breaks the rules of bowling either by (a) using an inappropriate arm action; (b) overstepping the popping crease; (c) having a foot outside the return crease
- Wide – a penalty of one extra that is conceded by the bowler if he bowls so that the ball is out of the batsman's reach
- Bye – extra(s) awarded if the batsman misses the ball and it goes past the wicketkeeper to give the batsmen time to run in the conventional way (note that the mark of a good wicketkeeper is one who restricts the tally of byes to a minimum)
- Leg bye – extra(s) awarded if the ball hits the batsman's body, but not his bat, and it goes away from the fielders to give the batsmen time to run in the conventional way.
When the bowler has bowled a no ball or a wide, his team incurs an additional penalty because that ball (i.e., delivery) has to be bowled again and hence the batting side has the opportunity to score more runs from this extra ball.
The batsmen have to run (i.e., unless the ball goes to the boundary for four) to claim byes and leg byes but these only count towards the team total, not to the striker's individual total for which runs must be scored off the bat.