A couple questions about this:

1) Is this term even relevant any more?

2) Does this mean anything from a developer's stand point?

It is not exactly clear to me if this is a BIOS, architecture, bus or a combination. A piece of software I'm working on expects to see a "Description" of the system and currently windows machines report "AT/AT Compatible". Having been tasked to port this to Mac, I really don't know what a proper "Description" would be - this will most likely be omitted but I was wondering if anyone could provide some insight on the modern usage of this term.

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    Not adding this as an answer just yet, but IBM compatible PC goes back to the very old (1980s?) IBM PCs. Because they were so dominant the basic architecture kind of went into a de facto standard. But nobody calls it that anymore. The de facto standard specifies, for instance, the form factor (ATX, AT), the BIOS and it's extensibility through ISA (now dead) and later PCI. The architecture name x86 also comes from one of the first CPUs used in those IBM pcs: The Intel 8086. The modern "IBM compatible" machines could still run Windows 1 and Dos, this is what makes them so compatible. – sinni800 Nov 18 '11 at 0:44
  • 1
    1) Nope. 2) Meaningless given that the OS is the biggest factor limiting developers. – Daniel R Hicks Nov 18 '11 at 1:30
  • Mac runs on Intel. Components now tell the OS who they are and where their drivers can be found on the Internet. It's a whole different world. Enough said. – Fiasco Labs Nov 18 '11 at 2:44
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    You'd do well to omit that description from the Windows flavour, too. It's been some while since the PC/AT, and we've had PC97, PC98, PC99, and PC2001 since then. Your supposed "AT compatibles" probably don't have any ISA expansion slots, coprocessor chip sockets, or firmwares in ROM, for starters. – JdeBP Nov 18 '11 at 3:16

1) Is this term even relevant any more?

Not really. In the early days of home/personal computing, there were several computing platforms using various microprocessors. Hardware and software were typically incompatible between these platforms. As HW and SW manufacturers and users gravitated towards the IBM PC, computers (know as IBM clones) that were both hardware and software compatible to the original IBM PC were produced to take advantage of its popularity. Today the term "PC" is pretty much means an IBM-compatible or Wintel computer, and excludes other personal computers like Mac.

2) Does this mean anything from a developer's stand point?

Not really. Today all of the essential parameters for PCs are now standardized and agreed upon by most manufacturers, the most significant alliance being Microsoft and Intel, aka Wintel. Today new features like PCI or SATA are agreed to by some standards committee and/or hardware and software manufacturers/associations. New hardware products are typically introduced with full OS and application support. The boundary between the hardware and OS and application programs is much better defined and kept separate with DKIs (driver kernel interfaces) and APIs (application program interfaces), so that strict hardware imitation is not required any more.



The origins of this platform came with the decision by IBM in 1980 to market a low-cost single-user computer as quickly as possible in response to Apple Computer's success in the burgeoning microcomputer market. On 12 August 1981, the first IBM PC went on sale. There were three operating systems (OS) available for it but the most popular and least expensive was PC DOS, a modified version of 86-DOS, to which Microsoft acquired full rights from Seattle Computer Products. In a crucial concession, IBM's agreement allowed Microsoft to sell its own version, MS-DOS, for non-IBM platforms. The only proprietary component of the original PC architecture was the BIOS (Basic Input/Output System).

A number of computers of the time based on the 8086 and 8088 processors were manufactured during this period, but with different architecture to the PC, and which ran under their own versions of DOS and CP/M-86. However, software which addressed the hardware directly instead of making standard calls to MS-DOS was faster. This was particularly relevant to games. The IBM PC was sold in high enough volumes to justify writing software specifically for it, and this encouraged other manufacturers to produce machines which could use the same programs, expansion cards and peripherals as the PC. The 808x computer marketplace rapidly excluded all machines which were not functionally very similar to the PC. The 640 kB barrier on "conventional" system memory available to MS-DOS is a legacy of that period; other non-clone machines did not have this limit.

The original "clones" of the IBM Personal Computer were created without IBM's participation or approval. Columbia closely modeled the IBM PC and produced the first "compatible" PC (i.e., more or less compatible to the IBM PC standard) in June 1982 closely followed by Eagle Computer. Compaq Computer Corp. announced its first IBM PC compatible a few months later in November 1982—the Compaq Portable. The Compaq was the first sewing machine-sized portable computer that was essentially 100% PC-compatible. 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.

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