8-bit computing: Difference between revisions

Revision as of 21:13, 27 November 2022

Revision as of 03:00, 3 January 2023

Line 21:

8-bit CPUs use an [[octet (computing)|8-bit]] [[Bus (computing)|data bus]] and can therefore access 8 bits of data in a single [[Instruction (computer science)|machine instruction]]. The address bus is typically a double octet ([[16-bit computing|16 bit]]s) wide, due to practical and economical considerations. This implies a direct [[address space]] of 64 [[kilobyte|KB]] (65,536 bytes) on most 8-bit processors.

Most [[home computer]]s from the 8-bit era fully exploited the address space, such as the [[BBC Micro]] (Model B) with 32&nbsp;KB of [[random-access memory|RAM]] plus 32&nbsp;KB of [[read-only memory|ROM]]. Others like the very popular [[Commodore 64]] had full 64&nbsp;KB RAM, plus 20&nbsp;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);<ref>{{Cite web|title=Bank Switching - C64-Wiki|url=https://www.c64-wiki.com/wiki/Bank_Switching|access-date=2021-04-08|website=www.c64-wiki.com}}</ref> without exploiting [[bank switching]], which allows for breaking the 64&nbsp;KB (RAM) limit in some systems. Other computers would have as low as 1&nbsp;KB (plus 4&nbsp;KB ROM), such as the Sinclair [[ZX80]] (while the later very popular Sinclair [[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 wouldn't 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&nbsp;KB, i.e. 128&nbsp;KB RAM, also the [[BBC Master]] with it expandable to 512&nbsp;KB of RAM.

{{Further|Zero page}}