8-bit computing
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Computer architecture bit widths |
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Bit |
Application |
Binary floating-point precision |
Decimal floating-point precision |
In
The term '8-bit' is also applied to the
The
The first widely adopted 8-bit
Historical context
8-bit microprocessors were the first widely used microprocessors in the computing industry, marking a major shift from mainframes and minicomputers to smaller, more affordable systems. The introduction of 8-bit processors in the 1970s enabled the production of personal computers, leading to the popularization of computing and setting the foundation for the modern computing landscape.
Details
An 8-bit register can store 28 different values. The range of integer values that can be stored in 8 bits depends on the integer representation used. With the two most common representations, the range is 0 through 255 (28 − 1) for representation as an (unsigned) binary number, and −128 (−1 × 27) through 127 (27 − 1) for representation as two's complement.
8-bit CPUs use an
Most home computers from the 8-bit era fully exploited the address space, such as the BBC Micro (Model B) with 32 KB of RAM plus 32 KB of ROM. Others like the very popular Commodore 64 had full 64 KB RAM, plus 20 KB ROM, meaning with 16-bit addressing you could not use all of the RAM by default (e.g. from the included BASIC language interpreter in ROM);[2] without exploiting bank switching, which allows for breaking the 64 KB (RAM) limit in some systems. Other computers would have as low as 1 KB (plus 4 KB ROM), such as the Sinclair ZX80 (while the later very popular ZX Spectrum had more memory), or even only 128 bytes of RAM (plus storage from a ROM cartridge), as in an early game console Atari 2600 and thus 8-bit addressing would have been enough for the RAM, if it would not have needed to cover ROM too). The Commodore 128, and other 8-bit systems, meaning still with 16-bit addressing, could use more than 64 KB, i.e. 128 KB RAM, also the BBC Master with it expandable to 512 KB of RAM.
While in general 8-bit CPUs have 16-bit addressing, in some architectures you have both, such as in the
Notable 8-bit CPUs
The first commercial 8-bit processor was the
Another notable 8-bit CPU is the
Manufacturer | Processor | Year | Comment |
---|---|---|---|
Intel | 8008 | 1972 | Datapoint 2200 compatible |
Signetics | 2650 | 1973 | |
Intel | 8080 | 1974 | 8008 source compatible |
Motorola | 6800 | 1974 | |
Fairchild | F8 | 1975 | |
MOS | 6502 | 1975 | Similar to 6800, but incompatible |
Microchip | PIC |
1975 | Harvard architecture microcontroller |
Electronic Arrays | EA9002 |
1976 | 8-bit data, 12-bit addressing |
RCA | 1802 | 1976 | |
Zilog | Z80 | 1976 | 8080 binary compatible |
Intel | 8085 | 1977 | 8080 binary compatible |
Zilog | Z8 | 1978 | Harvard architecture microcontroller |
Motorola | 6809 | 1978 | 6800 source compatible |
Intel | 8051 |
1980 | Harvard architecture microcontroller |
Motorola | 68008 | 1982 | 32-bit registers, 20-bit or 22-bit addressing, three 16-bit ALUs, 8-bit data bus; Motorola 68000 software-compatible, 6809 hardware-compatible |
MOS | 6510 | 1982 | Enhanced 6502 custom-made for use in the Commodore 64 |
Ricoh | 2A03 | 1982 | 6502 clone minus BCD instructions for the Nintendo Entertainment System |
Zilog | Z180 | 1985 | Z80 binary compatible |
Motorola | 68HC11 |
1985 | |
Hudson | HuC6280 | 1987 | 65C02 binary compatible |
Atmel | AVR |
1996 | |
Zilog | EZ80 | 1999 | Z80 binary compatible |
Infineon |
XC800 | 2005 | |
Freescale | 68HC08 |
? | |
Motorola | 6803 | ? | |
NEC | 78K0[3] |
? |
Use for training, prototyping, and general hardware education
8-bit processors continue to be designed today for general education about computer hardware, as well as for hobbyists' interests. One such CPU was designed and implemented using
See also
References
- (PDF) from the original on 2017-08-10.
- ^ "Bank Switching - C64-Wiki". www.c64-wiki.com. Retrieved 2021-04-08.
- ^ "NEC 78K0". NEC. Archived from the original on 2008-10-28. Retrieved 2009-02-10.
- Motherboard. Retrieved November 4, 2021.
- ^ Constantino, Paulo. Homebuilt 8-bit CPU + Computer with graphics and sound made from scratch using 74HC Logic.