Games - IBM PC compatible

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IBM PC compatible refers to a class of computers which make up the vast majority of smaller computers (microcomputers) on the market today. They are based (without IBM's participation) on the original IBM PC. They use the Intel x86 architecture (or an architecture made to emulate it) and are capable of using interchangeable commodity hardware. These computers also used to be referred to as PC clones, and nowadays, just PCs.

In addition, most modern x86 server-class machines are IBM PC compatible, being essentially a more robust version of the modern desktop PC.

History

Origins

The origins of this platform came with the decision by IBM in 1980 to market a personal computer as quickly as possible in response to Apple Computer's rapid success in the burgeoning market for low-cost single-user computers — what later came to be known as the "personal computer market". On 12 August 1981, the first IBM-PC went on sale. There were several operating systems available for it but the best remembered is DOS (the cheapest). IBM licensed DOS from Microsoft; IBM's version was called PC-DOS and was sold as an "add-on" to the IBM PC. In a crucial concession almost unnoticed by either party at the time, IBM's agreement also allowed Microsoft to sell its version, MS-DOS, for non-IBM platforms. Also, in creating the platform, IBM used only one proprietary component: The BIOS.

Columbia copied the IBM PC and produced the first 'compatible' (i.e., more or less compatible to the IBM PC standard) PC in 1982. Compaq Computer Corp. produced its first IBM PC compatible a few months later in 1982 — the Compaq Portable
. The Compaq was not only the first "sewing machine-sized" portable PC but, even more important, was the first essentially 100% PC-compatible computer. The company could not directly copy the BIOS as a result of the court decision in Apple v. Franklin, but it could reverse-engineer the IBM BIOS and then write its own BIOS using clean room design. Compaq became a very successful PC manufacturer, and was bought out by Hewlett-Packard in 2002.

Compatibility issues

Simultaneously, many manufacturers such as Xerox, Digital, Sanyo, and Wang introduced PCs that were, although x86- and MS-DOS-based, not completely hardware-compatible with the IBM PC. While such decisions seem foolish in retrospect, it is not always appreciated just how fast the rise of the IBM clone market was, and the degree to which it took the industry by surprise. The pre-existing home computer marketplace supported machines based on a wide variety of hardware, all running CP/M. Later, in 1987, IBM itself would launch the PS/2 line of personal computers which was only software compatible with the PC architecture; this was also hugely unsuccessful.

Microsoft's intention, and the mindset of the industry from 1981 to as late as the mid-1980s, was that application writers would write to the API's in MS-DOS, and in some cases to the firmware BIOS, and that these components would form what would now be called a hardware abstraction layer. Each computer would have its own OEM version of MS-DOS, customized to its hardware. Any piece of software written for MS-DOS would run on any MS-DOS computer, regardless of variations in hardware design.

During this time MS-DOS was sold only as an OEM product. There was no Microsoft-branded MS-DOS, MS-DOS could not be purchased directly from Microsoft, and the manual's cover had the corporate color and logo of the PC vendor. Bugs were to be reported to the OEM, not to Microsoft. However, in the case of the clones, it soon became clear that the OEM versions of MS-DOS were virtually identical, except perhaps for the provision of a few utility programs.

MS-DOS provided adequate support for character-oriented applications, such as those that could have been implemented on a minicomputer and a Digital VT100 terminal. Had the bulk of commercially important software fallen within these bounds, hardware compatibility might not have mattered. However, from the very beginning, many significant pieces of popular commercial software wrote directly to the hardware, for a variety of reasons:

Communications software directly accessed the UART chip, because the MS-DOS API and the BIOS did not provide full support for the chip's capabilities.
Graphics capability was not taken seriously. It was considered to be an exotic or novelty function. MS-DOS didn't have an API for graphics, and the BIOS only included the most rudimentary of graphics functions (such as changing screen modes and plotting single points); having to make a BIOS call for every point drawn or modified also increased overhead considerably, making the BIOS interface notoriously slow. Because of this, line-drawing, arc-drawing, and blitting had to be performed by the application, and this was usually done by bypassing the BIOS and accessing video memory directly. Games, of course, used graphics. They also performed any machine-dependent trick the programmers could think of in order to gain speed. Thus, games were machine-dependent — and games turned out to be important in driving PC purchases.
Even for staid business applications, speed of execution was a significant competitive advantage. This was shown dramatically by Lotus 1-2-3
's competitive knockout of rival Context MBA. The latter, now almost forgotten, preceded Lotus to market, included more functions, was written in Pascal, and was highly portable. It was also too slow to be really usable on a PC. Lotus was written in pure assembly language and performed some machine-dependent tricks. It was so much faster that Context MBA was dead as soon as Lotus arrived.
Disk copy-protection schemes, popular at the time, worked by reading nonstandard data patterns on the diskette to verify originality. These patterns were difficult or impossible to detect using standard DOS or BIOS calls, so direct access to the disk controller hardware was necessary for the protection to work.
The microcomputer programming culture at the time was hacker-like, and enjoyed discovering and exploiting undocumented properties of the system.

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