Evolution of the Personal Computer – a Remembered History

The following is an article I wrote on Quora in response to a question about the evolution of the personal computer.  Looking back at the 45-year history of the “personal confuser” as we sometimes call those devices we now can’t seem to live without.  Realizing that most of the population was born into a world where the PC has always been there, it is sometimes important to remember where we came from and how we got here.

Soon after the development of the microprocessor, in the early 1970s, the Altair 8000 appeared on the market in 1975, powered by the Intel 8080 8-bit CPU. Many more 8-bit machines followed, coupled with keyboards and CRT monitors, though many of the early machines intended for home use used television sets for monitors, connected through a video to TV converter outputting an NTSC signal on VHF channel 3 or 4.

Commodore introduced the PET computer, a complete unit with keyboard and monitor in one desktop case, which ran a version of BASIC as an operating system. In the early 1980s, a home version, the Commodore VIC-20, was introduced, with the computer built into an enlarged keyboard, with a cartridge tape drive for data, and video output to an optional CRT monitor or a TV converter. These machines had a whopping 5KB of memory.

A number of smaller, more portable machines appeared, all with BASIC as the operating system, stored in various incompatible byte-code forms. Tandy Corp. sold the Radio Shack TRS-80 (which stood for Tandy Radio Shack w/ 8080 CPU), which promptly got the moniker “Trash-80” from critics. Chip-maker Texas Instruments, which had earlier killed the mechanical slide rule market with their hand-held calculators, came out with the TI-99 computer. Another low-cost compact machine was from Timex. Most of these machines used the MOS 6502 8-bit microprocessor, or the Zilog Z-80.

Steve Jobs and Steve Wozniak came out with the Apple computer, which, in Jobs’ inimitable marketing instincts, was named Apple II in the production model, to give the impression that it was a new and improved version of an earlier model, actually a prototype built in a wooden box. Apple would become one of the most successful of the early personal computers.

About the time Jobs and Wozniak were tinkering, Gary Kildahl, also in California, was experimenting with uses for the 8-bit Intel microprocessor, came up with a loader and command shell for a Winchester hard disk, which he named CP/M, Control Program for Microprocessors, introducing the concept of a block-structured disk operating system and a command shell that wasn’t BASIC. Prior computers were capable of running machine-code programs directly in addition to BASIC, but CP/M was the first to emphasize using binary programs on disk as the primary operating mode.

Some of the first commercial CP/M machines were the Osborne I luggable computer, which featured a 360-KB 5–1/4″ floppy drive, a 16×64-character CRT terminal, and a detachable keyboard in the lid of a suit-case-sized case that weighed over 15 kg. Kaypro came out with a similar form factor CP/M machine that was more suitable for desktop use, with a larger display screen and keyboard.

With the introduction of the 16-bit 8086 CPU from Intel, IBM became interested in adding a microprocessor-based system to their business line of mainframes and terminals, first approaching Kildahl’s Digital Research, developers of CP/M, and Bill Gates’ fledgling Microsoft, which had gotten its start writing BASIC interpreters for the Altair and other hobbyist microprocessor-based systems, and had recently acquired a 16-bit independent rewrite of CP/M, which, with the addition of some concepts from Xenix, a micro-processor-based version of Unix that Microsoft had licensed, became MS-DOS, the Disk Operating System. IBM adopted MS-DOS as PC-DOS for its new personal computer, the IBM PC, which featured an open system design that allowed third-party vendors to develop add-on hardware and write device drivers for it, which, of course, led to the proliferation of “IBM clones” from many different manufacturers.

By this time, the successful marketing of the Osborne and Kaypro CP/M machines and the Apple II had spawned a flurry of software development companies building business software that would run on the desktop without requiring a mainframe back-end, including spreadsheets, project planning software, and word processors. Stand-alone word processing workstations had sprung up with the microprocessor revolution, but were single-purpose machines, relegated to the “typing pool” at large corporations and document-preparation companies. With the introduction of a desktop machine from IBM, then the largest computer company on the planet, those vendors quickly ported their products to the 16-bit MS-DOS platform, and CP/M faded from the market, in part due to the untimely death of its founder.

Microsoft solidified its grip on the personal computer operating system market with exclusive contracts with various PC manufacturers. Apple focused its market on education and the arts, moving to the wider word-size market with the Motorola 68000, a 32-bit CPU with a 16-bit data bus, and a graphical desktop system based on the Xerox Palo Alto Research Center (PARC) Star project. The Macintosh was introduced in 1984. Microsoft countered with the Windows desktop environment running on top of MS-DOS soon after.

IBM commissioned a new graphical operating system to replace the Windows environment as 32-bit CPUs came into wide use in the early 1990s, but disputes between IBM and Microsoft led to the split into OS-2 on the IBM side and Windows 95 on the Microsoft side. Microsoft’s grip on the generic PC market won out, with OS/2 gradually fading away with the incompatibility between OS/2 and Windows 95 and Windows NT.

On the Unix side, Microsoft sold Xenix rights to the Santa Cruz Operation early on, which, after porting to 32-bit, became SCO Unix, but never got our of the small niche as a multi-user solution for small to medium-sized businesses. The mainframe Unix of the 1980s ported to high-end 32-bit microprocessor workstations used in academic and scientific research.

In 1990, Linus Torvalds, a college student in Finland, desiring a 32-bit alternative to the 16-bit micro-kernel teaching tool, Minix, built a new Unix-like monolithic 32-bit kernel, around which he and developers all over the world wrapped the GNU software collection from the Free Software Foundation, creating the GNU/Linux operating system, which has, in the 21st century, captured the network server market from Unix and replaced the Unix workstations on desktops of developers and research scientists, as well as taken over the hobby market started with the Altair 8000 in 1975, with re-purposed former Windows machines and the proliferation of tiny single-board computers, led by the Raspberry Pi.

The adaptable Linux kernel also became the core of Google’s Android operating system, which, along with iOS, the embedded version of the now BSD-Unix-based operating system adopted by Apple at the turn of the century, drives all the world’s handheld computing devices, the ultimate personal computers most of us carry with us everywhere, disguised as telephones, pagers, cameras, and music and video entertainment devices, as well as portals to the World Wide Web. Microsoft’s Windows system remains the default OS for the desktop and laptop environment, and the core server operating system in corporations—for now.