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   » » Wiki: 8-bit
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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 .


Details
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
8-bit data, 12-bit addressing
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

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