Video Random Access Memory

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As VRAM (short: VRAM , VRAM or WRAM ) is defined as DRAM , which especially in 1993 and 1994 to the millennium as local memory on graphics cards was applied. The most important property of the memory are two ports ( dual-ported RAM ), a "normal" one for random reading and writing ( random access ) and one for sequential reading (video signal generation).

Around the turn of the millennium, normal RAM became powerful enough, so that normal single ported RAM (DDR or GDDR) became sufficient for graphics cards.

In many computer magazines , VRAM is still used today to refer to the memory of a graphics card , regardless of the memory technology.

construction

Conceptually, VRAM consists of two parts:

  • SAM ( Serial Access Memory )
    The SAM interface is used to read the data for the RAMDAC to generate the video signal. Only sequential read accesses can be carried out. Access via the SAM interface (e.g. 110 Mbytes / s) is somewhat faster than that via the DRAM interface (e.g. 60 Mbytes / s) and hardly hinders access via the DRAM interface, as only very much rarely (every 2048, 4096 or 8192 bytes) the actual RAM has to be accessed.
  • DRAM ( Dynamic Random Access Memory )
    This memory interface is used for access by the CPU or integrated graphics functions of the graphics processor to create texts, graphics and images. Technologically, the VRAM module consists of either FPM RAM (30–40 ns cycle time) or EDO RAM (20–30 ns cycle time), which enables clock frequencies of 50 to 66 MHz.

Further developments

ET6000 with 2 MB MDRAM from MoSys.
  • Like VRAM, WRAM ( Window RAM ) is equipped with separate read and write lines, but offers faster access times and is cheaper to manufacture. For example, the Matrox MGA Millennium graphics cards and the Number Nine Revólution 3D “Ticket to Ride” feature WRAM.
  • SGRAM ( synchronous graphics RAM ) is a technology with SDRAM related single-ported memory, d. H. simultaneous read and write access is not possible. It offers a range of functions that has been expanded to include graphics operations (e.g. reading and writing in blocks) and higher clock frequencies.
  • MDRAM ( Multi-bank DRAM ) is structured as an array of independent memory banks that are connected via a common bus. A high degree of parallelization is possible with this structure. The Hercules Dynamite 128 graphics card ( GPU : Tseng Labs ET6000) has up to 4 MB MDRAM.
  • CDRAM ( Cache DRAM ) is a mixture of static memory ( SRAM ) and dynamic memory (DRAM). Similar to the cache of modern processors, frequently used data is stored in the fast SRAM with CDRAM, which leads to an increase in performance.
  • 3D RAM is a Mitsubishi development consisting of memory modules with integrated logic in between . Some graphic operations (e.g. buffer test) can be carried out directly in the memory. This memory is used in the UltraSparc from Sun Microsystems .
  • GDDR-SDRAM ( Graphics Double Data Rate SDRAM ) is a graphics memory based on DDR-SDRAM , which is characterized by optimized access times and high clock frequencies.