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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.
Dual-ported video RAM (VRAM) is a dual-ported RAM variant of dynamic RAM (DRAM), which was once commonly used to store the Framebuffer in Graphics card, . Dual-ported RAM allows the CPU to read and write data to memory as if it were a conventional DRAM chip, while adding a second port that reads out data.
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.
Shared memory is an efficient means of passing data between programs. Depending on context, programs may run on a single processor or on multiple separate processors. Using memory for communication inside a single program, e.g. among its multiple threads, is also referred to as shared memory.
Memory-mapped I/O is preferred in IA-32 and x86-64 based architectures because the instructions that perform port-based I/O are limited to one register: EAX, AX, and AL are the only registers that data can be moved into or out of, and either a byte-sized immediate value in the instruction or a value in register DX determines which port is the source or destination port of the transfer.
DMA can also be used for "memory to memory" copying or moving of data within memory. DMA can offload expensive memory operations, such as large copies or scatter-gather operations, from the CPU to a dedicated DMA engine. An implementation example is the I/O Acceleration Technology.
The TI-99/4A has 256 bytes of scratchpad memory on the 16-bit bus containing the processor registers of the TMS9900 [2] Cyrix 6x86 is the only x86-compatible desktop processor to incorporate a dedicated scratchpad. SuperH, used in Sega's consoles, could lock cachelines to an address outside of main memory for use as a scratchpad.
In computer science, distributed memory refers to a multiprocessor computer system in which each processor has its own private memory. [1] Computational tasks can only operate on local data, and if remote data are required, the computational task must communicate with one or more remote processors.