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This article is about computer architecture. For other uses, see 8-bit (disambiguation).
Processors 1-bit 4-bit 8-bit 12-bit 16-bit 18-bit 24-bit 31-bit 32-bit 36-bit 48-bit 60-bit 64-bit 128-bit Applications 8-bit 16-bit 32-bit 64-bit Data Sizes bit nibble octet byte halfword word dword qword IEEE floating-point standard Single precision floating-point format (32-bit) Double precision floating-point format (64-bit) Quadruple precision floating-point format (128-bit) In computer architecture, 8-bit integers, memory addresses, or other data units are those that are at most 8 bits (1 octet) wide. Also, 8-bit CPU and ALU architectures are those that are based on registers, address buses, or data buses of that size. 8-bit is also a term given to a generation of computers in which 8-bit processors are the norm.
The first widely adopted 8-bit microprocessor was the Intel 8080, being used in many hobbyist computers of the late 1970s and early 1980s, often running the CP/M operating system. The Zilog Z80 (compatible with the 8080) and the Motorola 6800 were also used in similar computers. The Z80 and the MOS Technology 6502 8-bit CPUs were widely used in home computers and game consoles of the '70s and '80s. Many 8-bit CPUs or microcontrollers are the basis of today's ubiquitous embedded systems.
There are 28 (256) possible values for 8 bits.
The first microprocessors had a 4-bit word length and were developed around 1970. The first commercial microprocessor was the BCD-based Intel 4004 (1971), developed for calculator applications. The first commercial 8-bit processor was the Intel 8008 (1972) which was originally intended for intelligent terminals. Most competitors to Intel started off with such character oriented 8-bit microprocessors. Modernized variants of these 8-bit machines are still one of the most common types of processor in embedded systems.
Important 8-bit CPUs
Eight-bit CPUs use an 8-bit data bus and can therefore access 8 bits of data in a single machine instruction. The address bus is typically a double octet wide (i.e. 16-bit), due to practical and economical considerations. This implies a direct address space of only 64 KiB on most 8-bit processors.
Early and/or popular 8-bit processors (incomplete):
- Intel 8008 (1972 Datapoint 2200 compatible)
- Intel 8080 (1974 8008 source compatible)
- Motorola 6800 (1974)
- MOS Technology 6502 (1975 similar to 6800, but incompatible)
- Zilog Z80 (1976 8080 binary compatible)
- Intel 8085 (1977 8080 binary compatible)
- Zilog Z8 (1978 Harvard architecture microcontroller)
- Motorola 6809 (1978 partially 6800 compatible)
- Intel 8051 (1980 Harvard architecture microcontroller)
- Zilog Z180 (1985 Z80 binary compatible)
- Zilog eZ80 (1999/2001 Z80 binary compatible)
- Motorola 6803
- Freescale 68HC08
- Freescale 68HC11
- RCA 1802
- Hudson Soft HuC6280
- PIC microcontroller
- Atmel AVR family microcontrollers
- NEC 78K0 series * Infineon XC800 family microcontrollers
See also
- History of video game consoles (third generation)
- Vasm, a free assembler
CPU technologies Architecture Parallelism PipelineLevelThreadsTypes Components Arithmetic logic unit (ALU) · Barrel shifter · Floating-point unit (FPU) · Back-side bus · Multiplexer · Demultiplexer · Registers · Memory management unit (MMU) · Translation lookaside buffer (TLB) · Cache · Register file · Microcode · Control unit · Clock ratePower management Categories:- Data unit
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