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Tag Wiki '8-bit'.


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'''8-bit''' is also a generation of [[microcomputer]]s in which 8-bit [[microprocessor]]s were the norm.

The IBM System/360 introduced byte-addressable memory with 8-bit bytes, as opposed to bit-addressable or decimal digit-addressable or word-addressable memory, although its general purpose registers were 32 bits wide, and addresses were contained in the lower 24 bits of those addresses. Different models of System/360 had different internal data path widths; the IBM System/360 Model 30 (1965) implemented the 32-bit System/360 architecture, but had an 8 bit native path width, and performed 32-bit arithmetic 8 bits at a time.

The first widely adopted 8-bit was the Intel 8080, being used in many hobbyist computers of the late 1970s and early 1980s, often running the CP/M ; it had 8-bit data words and 16-bit addresses. 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 and second- and third-generation game consoles of the 1970s and 1980s. Many 8-bit CPUs or are the basis of today's ubiquitous .

There are 28 (256) different possible values for 8 bits. When unsigned, it has possible values ranging from 0 to 255, when , it has -128 to 127.

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 of only 64  on most 8-bit processors.

Notable 8-bit CPUs
The first commercial 8-bit processor was the Intel 8008 (1972) which was originally intended for the Datapoint 2200 intelligent terminal. 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.

Another notable 8-bit CPU is the MOS Technology 6502; it, and variants of it, were used in a number of personal computers such as the and , the Atari 8-bit family, the , and the and Commodore VIC-20, and in a number of video game consoles such as the Atari 2600 and the Nintendo Entertainment System.

+ Early or popular 8-bit processors (incomplete) ! Manufacturer ! Processor ! Year ! Comment
Datapoint 2200 compatible
8008 source compatible
Similar to 6800, but incompatible
Harvard architecture microcontroller
8080 binary compatible
8080 binary compatible
6800 source compatible
Harvard architecture microcontroller
Harvard architecture microcontroller
Enhanced 6502 custom-made for use in the Commodore 64
6502 clone minus BCD instructions for the Nintendo Entertainment System
Z80 binary compatible
Z80 binary compatible

See also
  • , a free assembler

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