Shared graphics memory: Difference between revisions

Revision as of 10:52, 22 March 2012

Revision as of 22:36, 26 June 2012

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== History ==

Most early personal computers used a shared memory design with graphics hardware sharing memory with the CPU. Such designs saved money as a single bank of DRAM could be used for both display and program. Examples of this include the Apple II computer, the Commodore 64, the Radio Shack Color Computer, the Atari ST, and the Apple Macintosh.

The first PC to use the SMA was the [[IBM PCjr]], released in 1984. [[Video memory]] was shared with the first 128KiB of RAM. The exact size of the video memory could be reconfigured by software to meet the needs of the current program.

A notable exception was the IBM PC. Graphics display was facilitated by the use of an expansion card with its own memory plugged into an ISA slot.

Another early design was the [[Commodore International|Commodore]] [[Amiga]], introduced in 1985. It initially featured 256 [[Kibibyte|KiB]] of "[[chip RAM]]" (later up to 2048 KiB, depending on the model). This RAM was used by both the CPU (as main memory) and the Amiga's [[Original Amiga chipset|custom chipset]] (for sound/graphics/IO). By default, most Amiga computers were shipped with chip RAM only, but could be expanded with RAM that only the CPU could access (called "Fast RAM"), through expansion boards.

The first IBM PC to use the SMA was the [[IBM PCjr]], released in 1984. [[Video memory]] was shared with the first 128KiB of RAM. The exact size of the video memory could be reconfigured by software to meet the needs of the current program.

An early hybrid system was the Commodore Amiga which could run as a shared memory system, but would load executable code preferentially into non-shared "fast ram" if it was available.

== See also ==