Personal computing never would have gotten started if not for the invention of microprocessors, which puts a computer’s CPU (central processing unit) on a single chip – sometimes with companion chips. Intel released the first commercial CPU in 1971, and the first 8-bit “home computers” arrived just a few years later.

Chips and Kits

The Intel 8008 was the first 8-bit CPU, introduced by Intel in April 1972. The first personal computer based on the 8008 was the SCELBI, which was available assembled or in kit form. With 1 KB of RAM, the kit sold for US$565 and was first advertised in the March 1974 issue of QST, a ham radio magazine.

The 8008’s successor chip, the Intel 8080, was released in April 1974 as an improvement that was also backward compatible with the 8008. This was the CPU used in the MITS Altair 8800, the first really successful personal computer.

This inspired the Zilog Z-80 CPU, which is backward compatible with the 8080 but has an enhanced instruction set, a better interrupt system, and more registers. (The Z-80 was designed by a former member of the Intel team.) Intel would later counter with the 8085. Of the three CPUs, all are supported by CP/M, but the Z-80 had the most success in home computing, perhaps most notably in the TRS-80 sold by Radio Shack.

The competing chip architecture began with the Motorola 6800, which was in many respects comparable to the 8080 and Z-80. All these chips had an 8-bit data bus, a 16-bit address bus to access up to 64 KB of memory, a 16-bit stack pointer, and they even came in the same type of 40-pin package. The 6800 had fast access to the first 256 bytes of memory, addressed I/O devices as memory and thus didn’t need special I/O instructions, and supported direct memory access (DMA), which meant data could be read from a disk directly to memory with no load on the CPU. (The 8080 had more internal registers and did have special I/O instructions.)

The MOS Technology 6502 CPU was developed by former members of the Motorola 6800 team, and it was specifically aimed at potential customers of the 6800 who thought the CPU was too expensive. The goal was a more cost effective CPU, and the 6502 turned out to be that in spades. The 6502 sold for $25 on its release, a far cry from the $175 and up price of competing chips.

This is why Steve Wozniak decided to design the Apple 1 computer (left) around the 6502 CPU. Of course, Motorola responded by cutting the cost of the 6800 to $69, but the 6502 was still the price champion.

Apple, Commodore, Atari, and Acorn would all use the 6502 in their home computers.

One more 8-bit CPU had a role in home computing, the Motorola 6809E. It is best known as the heart of the Radio Shack TRS-80 Color Computer, which first shipped in the second half of 1980. The 6809 was also used in several other personal computers, none nearly as well known as Radio Shack’s CoCo.

Personal computing soon divided into two categories: home computers that had their own operating system and business computers that ran CP/M from Digital Research, a forerunner of MS-DOS. This article skips CP/M machines to focus on the home and education market.

Personal Computer Prehistory

• 1921: Radio Shack founded to serve amateur radio hobbyists
• 1928: Motorola begins as Galvin Manufacturing Corporation
• 1951: Texas Instruments (TI) founded
• 1954: TI develops the first transistor, designs first transistor radio
• 1954: Commodore Business Machines founded to sell typewriters
• 1955: Motorola begins producing transistors
• 1958: TI creates the first integrated circuit
• 1961: TI creates the first computer with integrated circuitry

The Modern Age

• 1972: Atari founded to develop video games
• March 1974: Motorola announces 6800 CPU, which ships by year-end
• April 1974: Intel 8080 CPU introduced, an improved version of the 8008
• January 1975: MITS Altair 8800 introduced at $439 as kit, $621 assembled, memory and interfaces at additional cost, considered the spark that would ignite the personal computer revolution
• 1975: MOS Technology introduces the 6502 CPU, aimed at the Motorola 6800.
• 1976: TI-30 scientific calculator introduced at $25
• April 1, 1976: Apple Computer founded
• 1976: MOS Technology introduced KIM-1 at $245, the first single-board computer kit, beating the Apple 1 to market
• July 1976: Zilog Z-80 CPU launched, designed to replace Intel 8080
• July 1976: Apple 1 goes on sale for $666, first single-board computer with a fully assembled system board, first color output, only 200 produced, discontinued September 30, 1977.
• 1976: Intel 8085 introduced to improve upon 8080 and target Zilog Z-80

Home and Personal Computers

• June 10, 1977: Apple II introduced at $1,298 with 4 KB RAM, 8 expansion slots, full-stroke keyboard. Apple II line discontinued in 1993 with 5-6 million units produced
• August 3, 1977: TRS-80 Model I introduced at Radio Shack stores across the US at $399 with 4 KB RAM – $599 with black-and-white monitor and cassette tape recorder
• September 11, 1977: Atari 2600 VCS game console comes to market
• October 1977: Commodore PET 2001 introduced at $495 with 4 KB RAM, first all-in-one computer with built-in monitor and tape drive
• October 1979: Texas Instruments TI-99/4 introduced at $1,050 with 13″ color monitor, first 16-bit personal computer
• Mid 1979: VisiCalc goes on sale, first electronic spreadsheet, and Apple II computers enter the office so executives can use VisiCalc
• November 1979: Atari 400 and 800 begin to ship
• 1980: Sinclair ZX80 introduced in UK, available prebuilt or in kit form
• 1980: Acorn Atom introduced in UK, available in kit or assembled
• July 31, 1980: Tandy introduces the Radio Shack TRS-80 Color Computer at $399 with 4 KB of memory.
• September 1980: Commodore VIC-1001 introduced in Japan, essentially a VIC-20 with Japanese Katakana characters instead of PETSCII, causing several potential Japanese competitors to discontinue or postpone their plans to enter the US market.
• November 1980: Motorola introduces 32-bit 68000 CPU with 16-bit data bus
• January 1981: Commodore VIC-20 goes on sale in North America at $299, first computer of any type to sell 1 million units
• 1981: BBC Micro debuts, ends up with 80% of the UK education market
• August 12, 1981: IBM PC goes on sale, giving personal computers a leg up in entering the workplace. Technically a 16-bit computer, but because of its significance, we have to mention it here.
• July 1982: Timex enters the market with the Timex Sinclair 1000 at $100, selling 600,000 units. Timex left the US market in 1984.
• August 1982: Commodore 64 introduced at $595, goes on to become the best selling model in the history of computing
• June 1983: TI-99/4A released at $525, monitor no longer included
• June 1983: Mattel Aquarius released at $160, discontinued October 1983
• October 1983: Coleco Adam introduced at $725, discontinued January 1985
• October 1983: TI exits home computer market
• 1984-85: Apple Macintosh, Atari ST, and Commodore Amiga 1000 launch the next generation of personal computing built around a 32-bit CPU – they all chose the Motorola 68000
• 1985: Intel introduces 32-bit 80386 CPU
• 1986: PC world begins using 32-bit 80386 CPU (64-bit x86 CPUs didn’t arrive until 2000)
• 1991: Atari phases out its 8-bit line
• November 1993: Apple IIe discontinued, last 8-bit Apple
• April 1994: Commodore declares bankruptcy, ceases to exist

After 8-Bit Computing

• May 1994: Apple introduces first PowerPC Macs, which remain 32-bit until the PowerPC 970 (a.k.a. G5) is introduced in 2002, although even OS X 10.5 Leopard, the last OS version for PowerPC Macs, makes very little use of it 64-bit capabilities
• January 2006: Apple begins switch to Intel x86 CPUs with Core Duo models, a chip based on the 32-bit Pentium M design
• August 2006: Mac Pro is the first Intel Mac with a 64-bit CPU
• September 2006: first consumer Macs to use Core 2 Duo chips, which are 64-bit processors
• April 2010: First Macs to use Intel Core i CPUs.

Resources

• Home Computer, Wikipedia
• History of Personal Computers, Wikipedia

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