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Video memory was shared with the first 128 KiB 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.
A shared memory system is relatively easy to program since all processors share a single view of data and the communication between processors can be as fast as memory accesses to the same location. The issue with shared memory systems is that many CPUs need fast access to memory and will likely cache memory, which has two complications:
Video random-access memory (VRAM) is dedicated computer memory used to store the pixels and other graphics data as a framebuffer to be rendered on a computer monitor. [1] It often uses a different technology than other computer memory, in order to be read quickly for display on a screen.
With shared video memory, an application must constantly check that it is only writing to memory that belongs to that application. When running a high-bandwidth video application such as a movie player or some games, the computing power and complexity needed to perform constant clipping and checking negatively impacts performance and compatibility.
Under the Amiga architecture, the direct memory access (DMA) controller is integrated into the Agnus (Alice on AGA models) chip. Both the CPU and other members of the chipset have to arbitrate for access to shared RAM via Agnus. This allows the custom chips to perform video, audio, or other DMA operations independently of the CPU.
Diagram of a symmetric multiprocessing system. Symmetric multiprocessing or shared-memory multiprocessing [1] (SMP) involves a multiprocessor computer hardware and software architecture where two or more identical processors are connected to a single, shared main memory, have full access to all input and output devices, and are controlled by a single operating system instance that treats all ...
The G200 is a 2D, 3D, and video accelerator chip for personal computers designed by Matrox. It was released in 1998. ... Millennium G200 received the new SGRAM memory ...
The TMS9918A's method of accessing the video RAM is slower than direct access, as used in unified-memory computers, because accessing video memory involved first outputting the low- then the hi-byte of the (14-bit) video memory address to I/O port $99, then one or more bytes of 8-bit data to port $98.