The Use of MS-DOS On Non IBM PC Compatible X86 Based Systems
In the beginning, when the IBM PC did not yet dominate the market, these x86-based systems were not clones of the IBM PC design, but had different internal designs, like the CP/M-based 8-bit systems that preceded them. Even a few years after the IBM PC's introduction, manufacturers such as Digital, HP, Sanyo, Tandy, Texas Instruments, Tulip Computers, NEC, Wang Laboratories, and Xerox continued to introduce personal computers that were barely, if at all, hardware-compatible with the IBM PC, even though they used x86 processors and ran MS-DOS. They used MS-DOS the way Microsoft had originally envisioned: in the same way as 8-bits systems used CP/M. They implemented standard ROM BIOS routines to achieve hardware independence as had 8080 (Z80) compatibles. So each machine had a different BIOS that, as long as software made only standard MS-DOS calls, would ensure compatibility.
But to get the best results out of the 8088's modest performance, many popular software applications were written specifically for the IBM PC. The developers of these programs opted to write directly to the computer's (video) memory and peripheral chips, bypassing MS-DOS and the BIOS. For example, a program might directly update the video refresh memory, instead of using MS-DOS calls and device drivers to alter the appearance of the screen. Many notable software packages, such as the spreadsheet program Lotus 1-2-3, and Microsoft's Microsoft Flight Simulator 1.0, directly accessed the IBM PC's hardware, bypassing the BIOS, and therefore did not work on computers that were even trivially different from the IBM PC. This was especially common among games. As a result, the systems that were not fully IBM PC-compatible couldn't run this software, and quickly became obsolete, and with them the concept of OEM versions of MS-DOS meant to run (through BIOS calls) on non IBM-PC hardware.
Read more about this topic: Influence Of The IBM PC On The Personal Computer Market
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