Mac Musings

Our Debt to the IBM PC

Daniel Knight - 2001.08.13 -

IBM introduced the PC, its first personal computer in August 1981. As I heard on the radio over the weekend, a fully configured system (including 64 KB RAM, two floppies, monitor, and printer) cost about $4,500. Just imagine what you could buy for that amount today!


For better or worse, our biggest debt to the IBM PC was creating a set of standards that would shape the personal computing industry, a field which had already been around for five years.

Prior to the PC, personal computers might be based on the 6502, 6809, Z80, or 8080, 8-bit processors capable of supporting 64 KB of memory. The new processors just coming into their own were the Motorola 68000, which IBM considered using, and the Intel 8086/8088, which IBM adopted. Today about 95% of all personal computers sold use processors descended from the Intel 8086.

Prior to the IBM PC, some computers used 8" floppies, and most personal machines used 5.25" floppies - each computer with its own disk format. One of the leading utilities for CP/M machines allowed them to read disks formatted for other CP/M computers. There was no compatibility between the Apple II, Atari, Commodore, TRS-80, and other non-CP/M brands. With the IBM PC, we had a standard 5.25" format, an ancestor of the format used on 3.5" floppy drives on today's PCs.

Prior to the PC, some computers had 24 lines of text, others 25. Some had 40 characters per line, others 64, and still others 80. Some even supported 132 characters - or as few as 22. With the IBM PC, the standard text format became 25 lines of 80 characters - or 40 characters on color displays.

The original IBM PC supported dual monitor work. You could have a monochrome text display and a color screen by using a monochrome display adapter and a color graphics adapter. The text display didn't support graphics, and the color display provided very low resolution text and graphics - 320 x 200 pixels.

Prior to the PC, there were a few competing standards for serial and parallel ports. Except for Apple, almost everyone has followed IBM's lead in that regard.

Prior to the PC, personal computers either ran a proprietary operating system or CP/M. Within a few years of the PC's introduction, the vast majority of computers ran MS-DOS, the ancestor of Microsoft Windows.

Microsoft has ported Windows NT to non-Intel hardware, specifically the Alpha and PowerPC processors, but it never made a dent outside of the Wintel market.

Competing Standards

Some companies tried to one-up IBM by offering higher density floppies, higher resolution graphics, better keyboard layouts, support for more than 640 KB of memory, industry standard busses, the 16-bit 8086 CPU, and some even had a second processor such as a Z80, 8080, or 8085 that could run CP/M.

The Zenith Z-100 and Texas Instruments Professional Computer are distant memories. They tried to offer a better solution, but being different doomed them. The same thing happened to NEC's Advanced Personal Computer, which was one of the few DOS machines to use 8" floppies. Doomed.

Clones succeeded initially based on how compatible they were with the standard IBM created. It didn't take long for the IBM PC, its descendants, and other DOS boxes to dominate the personal computing industry, shoving Atari, Commodore, and so many other brands to the sides and eventually out of the picture.

DOS and Windows

The IBM PC didn't ship with an operating system: The buyer could choose PC-DOS, CP/M-86, or the UCSD p-system. PC-DOS (IBM's name for MS-DOS) was cheaper; it won.

The next OS battle was between OS/2, a joint development of Microsoft and IBM, and Windows. Windows won and is the dominant operating system on the market today.

The second most popular OS on PC hardware is Linux, an operating system derived from Unix. It's very stable, very powerful, and has maybe 5% of the desktop computer market. On the other hand, Linux has become a leading server platform, where it apparently runs 20-30% of all servers on the Internet.

The other significant minority OS is the Mac OS, which is now split into "classic" and OS X. The classic Mac OS only runs on Macintosh computers and a handful of licensed clones. Although some have ported Darwin (part of OS X) to the PC architecture, Apple only sells OS X for G3- and G4-based Macs.

Between them, all of the minority platforms control about 10% of the personal computer market vs. about 90% for Windows.

Graphics Standards

The original monochrome display adapter supported a very high resolution screen, but it didn't do graphics. Hercules invented the Hercules Graphics Adapter, which allowed high resolution (720 x 350) graphics on IBM's monochrome display. HGA became a popular business standard.

The color graphics adapter supported 320 x 200 pixels with up to 4 colors. CGA eventually gave way to EGA, with 640 x 350 resolution, which later gave way to VGA (640 x 480). Today's PC monitors are descended from the VGA standard, and for the past several years Apple has adopted the same video port and standards to make it easier for Mac owners to buy monitors. (Let's not get started on Apple's digital video port....)


The original IBM PC didn't even have a hard drive option. It had two bays for full-height (about 3" high!) 5.25" floppy drives, five expansion slots, and enough sockets on the motherboard to support 256 KB of memory. The 8-bit expansion slots ran at the same 4.77 MHz as the CPU, which has a 16-bit processor designed to run on an 8-bit bus. (Sound familiar? Several Road Apples did the same kind of thing, running a 32-bit CPU on a 16-bit bus.)

IBM expanded that to a 16-bit bus with the IBM AT (for Advanced Technology) in 1984, a machine that also supported a high capacity 1.2 MB floppy disk. The 16-bit AT slots ran at the same 6 MHz speed as the CPU. As clones began to push the envelope, the question of bus speed vs. CPU speed became important, because a card that ran fine at 6 or 8 MHz might not work reliably at 10 or 12 MHz. Eventually the industry adopted 8 MHz as an ad hoc standard.

IBM tried to differentiate itself with Micro Channel Architecture (MCA), a new bus that never caught on with the PC industry. The rest of the industry created the EISA standard (Extended Industry Standard Architecture), which was later replaced by PCI (Peripheral Component Interconnect). That's the standard both Macs and PCs support today.

The first hard drives needed controller cards, but over the years manufacturers started building some of those electronics into the drive itself, eventually the IDE standard. IDE gave way to EIDE and ATA, followed by the Ultra/ATA standards used on PCs and Macs today.

In the end, we ended up with Macs and PCs using mostly the same parts, not counting the main processor, as Apple adopted standard parts to keep costs down.

The IBM PC Legacy

More than anything else, IBM legitimized personal computers as business machines. The standard architecture IBM pioneered using off-the-shelf components allowed Microsoft to become the behemoth it is today. And the sheer size of the Wintel industry has made standard components readily affordable, allowing anyone to build their own clone and Apple to reduce the cost of building Macs by using many of those same components.

The great irony is that Apple, then a dominant player in the personal computing industry, welcomed IBM in 1981. The IBM PC lead to the marginalization of Apple, and Microsoft managed to turn IBM into a bit player in the PC industry. Today IBM and Apple are partners in certain areas, particularly the PowerPC processor.

Personal computers have gone from an expensive hobby to something most households seem to have and businesses can't imagine being without. That's the biggest part of the IBM PC legacy.

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Dan Knight has been using Macs since 1986, sold Macs for several years, supported them for many more years, and has been publishing Low End Mac since April 1997. If you find Dan's articles helpful, please consider making a donation to his tip jar.

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