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→Notable 8-bit CPUs: 8085 was introduced March 1976. The 2650 was introduced in 1975 although designed earlier. |
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Most [[home computer]]s from the 8-bit era fully exploited the address space, such as the [[BBC Micro]] (Model B) with 32 KB of [[random-access memory|RAM]] plus 32 KB of [[read-only memory|ROM]]. Others like the very popular [[Commodore 64]] had full 64 KB RAM, plus 20 KB ROM, meaning with 16-bit addressing not all of the RAM could be used by default (e.g. from the included [[BASIC]] language interpreter in ROM);<ref>{{Cite web|title=Bank Switching - C64-Wiki|url=https://www.c64-wiki.com/wiki/Bank_Switching|access-date=8 April 2021|website=www.c64-wiki.com}}</ref> 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 (memory)|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
Some [[index register]]s, such as the two in the 6502, are 8-bit. This limits the size of the arrays addressed using [[indexed addressing]] instructions to objects of up to 256 bytes without requiring more complicated code. Other 8-bit CPUs, such as the [[Motorola 6800]] and [[Intel 8080]], have 16-bit index registers.
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