How Fast Were Those Late 1970s Home Computers?

Back in the early days of personal computing, benchmarks were usually written in BASIC and tweaked for each competing brand of computer and BASIC in use. This article looks at some popular benchmarks from the 8-bit era of home computing.

One way to find prime numbers is to go through an entire range of numbers and eliminate non-primes by removing multiples of 2, then 3, and so on for each subsequent prime number. This is known as the Sieve of Eratosthenes.

John Metcalf coded this into BASIC and posted his results on the Retro Programming website. Others then took his code, ran it on other home computers, and shared their results. Results are divided among CPU families and sorted by execution time in seconds – faster is better.


The 6502 and its derivatives were used in the Acorn, Apple II, Atari, BBC, and Commodore 8-bit computers.

  • BBC Master, 2.0 MHz 65SC12, 76
  • BBC Micro Model B, 2.0 MHz 6502, 101
  • Apple IIe, 1.0 MHz 6502, Integer BASIC, 134
  • Acorn Electron, 2.0 MHz 6502, 138
  • Commodore 128, 2.0 MHz 8502, 152
  • Apple IIe, 1.0 MHz 6502, Applesoft BASIC, 211
  • Commodore VIC-20, 1.0 MHz 6502, 234
  • Commodore 64, 1.0 MHz 6510, 254
  • Commodore Plus/4, 1.8 MHz 8501, 267
  • Atari 800XL, 1.8 MHz 6502, 316
  • Atari 130XE, 1.79 MHz 6502C, 338

At 1.0 MHz, Apple is the fastest, Commodore a bit slower. The 2.0 MHz BBC Master wins overall, with the BBC Micro in second place. Even at 1.8 MHz, Atari BASIC lags far behind even the worst 1.0 MHz machine.


The Z-80 and Intel 8080 and 8085 were the most common family of CPUs competing with the MOS Technology 6502 family. Most of these systems run in the 2.0 to 4.0 MHz range.

  • Amstrad CPC464, 4.0 MHz Z-80, 140
  • Coleco Adam, 3.58 MHz Z-80, 174
  • Tandy 102, 2.4 MHz 80C85, 367
  • Sinclair Spectrum +3, 3.55 MHz Z-80, 388
  • TRS-80 Model I, 1.77 MHz Z-80, 421

The 4.0 MHz Amstrad CPC464 is comparable to the 2.0 MHz Acorn Electron, which goes with the experience of many Apple II and Commodore users that despite seemingly slow clock speeds, their 8-bit machines seemed more efficient MHz to MHz than chips in the Z-80 family.


  • Tandy CoCo 3, 1.79 MHz 6809E, 147
  • Tandy MC-10, 0.895 MHz 6803, 220
  • Tandy CoCo 2, 0.895 MHz 6809E, 271

With its twice-as-fast CPU, the Color Computer 3 easily outperformed the CoCo 10 and MC-10 – almost equalling the 4.0 MHz Amstrad CPU464 and edging out the 2.0 MHz Commodore 128.


The odd one out was the TMS99000 used in the Texas Instruments TI 99/4 and 99/4A. A 3 MHz 16-bit CPU hobbled by inexplicable design decisions on the computer’s logic board, it could have given TI a real edge over competing 8-bit platforms.