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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.
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.
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.
VESA BIOS Extensions (VBE) is a VESA standard, currently at version 3, that defines the interface that can be used by software to access compliant video boards at high resolutions and bit depths.
The amount of video memory is dependent upon the amount of pre-allocated video memory plus DVMT allocation. DVMT, as its name implies, dynamically allocates system memory for use as video memory to ensure more available resources for 2D/3D graphics performance, e.g. for graphically demanding games.
With 4 GiB or more of RAM installed, and with RAM occupying a contiguous range of addresses starting at 0, some of the MMIO locations will overlap with RAM addresses. On machines with large amounts of video memory, MMIO locations have been found to occupy as much as 1.8 GB of the 32-bit address space. [12]
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Dual-ported video RAM (VRAM) is a dual-ported variant of dynamic RAM (DRAM), which was once commonly used to store the framebuffer in graphics adapters.. 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.