1980s Vintage Computers

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IBM PC / XT / AT

The introduction of the IBM PC marked a major milestone in 1980's computing, and led to the growth of the PC compatible market, with the creation of companies such as Compaq, Dell and 3Com, and a major boost to the fortunes of Microsoft, Novell and Borland.

The IBM PC was launched at a time when the majority of desktop computers were 8-bit 8080 or Z80 based CP/M machines. The IBM PC was not the first ever computer to use a 16-bit processor (the 8088, which was a cheaper version of the 8086).

The main features that the IBM PC initially gave were as follows:

• One or two 360k 5.25" floppy drives (the first early models had 120k byte single sided drives).
• BASIC in ROM with cassette tape support.
• Option of CP/M-86 or IBM PC-DOS (re-badged MS-DOS).
• Wide range of off-the-shelf software eg VisiCalc, Wordstar, SuperCalc, dBase II, which were easily ported from 8-bit CP/M.
• Open platform for new software developments, from 8086 Assembler to a wide range of programming languages (eg PL/M, C, Basic).
• Choice of either a high-quality monochrome text display or colour display capable of 2-colour medium resolution or 4-colour low resolution graphics.
• Published hardware bus and layout design, allowing 3rd party add-ons.
• Options of serial port and Centronics parallel printer port.
• The IBM badge on the front, hence world-class sales and marketing support.

These advantages meant that other software companies and manufacturers of interface cards could port their products to the IBM PC, which led to more sales for IBM, and in turn lead to a growth in software and add-in card sales. This led to other computer manufactures to adapt their 8088/8086 machines to use the IBM PC bus (which became known as the ISA bus), and also modify their designs and versions of MS-DOS to run IBM PC applications without modification. Eventually this level of compatibility extended to the machines BIOS, so they would run IBM PC-DOS. 

The IBM PC was developed, and became a family of products over the years:
- IBM PC
- IBM XT (addition of a hard drive)
- IBM Portable PC
- IBM AT (80286 and the 16-bit  ISA bus)
- IBM XT/286

There was also variants to hook up to IBM mainframes (IBM 3270 PC) and for the home market (PC Jnr).

IBM then improved on the IBM AT by developing the IBM PS/2 range, the main impact being the change to the MCA bus. This was a major leap forward compared to ISA. Unfortunately the market did not agree, and the rival PCI bus became dominant and MCA went into decline. Some elements from the PS/2 family were successful, these included:

- 3.5" 1.44MB floppy format.
- PS/2 keyboard and mouse interface.
- VGA graphics.

PC clones became the norm, the most successful manufacturers offered slightly more advanced products, at a reasonable price, and on terms to suit the customer. IBM could not match their new competitors in a market they created, so went after new markets away from the desktop computer.

The story of how Microsoft (who produced PC-DOS for IBM) became a bigger company from IBM is covered in plenty of other places on the web and is the subject of several books on corporate dynamics.

IBM PC / XT / AT links

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