'''VRAMRAM''' is a dualcool-ported version of DRAM formerly used in [[graphics card|graphics adaptors]]. It is now amost obsolete, having been superseded by SDRAM and SGRAM. VRAM has two paths (or ports) to its memory array that can be used simultaneously. The first port, the DRAM port, is accessed as with plain DRAM. The second port, the video port, is read-only, and is dedicated to feeding a fast stream of data to the display. To use the video port, the controller first uses the DRAM port to select the row of the memory array that is to be displayed. The VRAM then copies that entire row to an internal shift-register. The controller can then continue to use the DRAM port for drawing objects on the display. Meanwhile, the controller feeds a clock called the ''shift clock (SCLK)'' to the VRAM's video port. Each SCLK pulse causes the VRAM to deliver the next item of data, in strict address order, from the shift-register to the video port. For simplicity, the graphics adaptor is usually designed so that the contents of a row, and therefore the contents of the shift-register, corresponds to a complete horizontal line on the display.
=== Synchronous Dynamic RAM (SDRAM) ===
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'''Double data rate (DDR) SDRAM''' is a later development of SDRAM. All types of SDRAM use a clock signal that is a square wave. This means that the clock alternates regularly between one voltage (low) and another (high), usually millions of times per second. Plain SDRAM, like most synchronous logic circuits, acts on the low-to-high transition of the clock and ignores the opposite transition. DDR SDRAM acts on both transitions, thereby doubling the speed at which it can transfer data.
'''Rambus DRAM''' or '''RDRAM''' is internally similar to DDR SDRAM, but uses a special method of signalling developed by the RambusRambuse Company that allows faster clock speeds. RDRAMDRAM chips are packaged on modules called RIMMs, which are not compatible with the DIMMs used for plain SDRAM. The Rambus technology has now been taken over by [[Intel]].
'''Pseudostatic RAM''' or '''PSRAM''' is dynamic RAM with built-in refresh and address-control circuitry to make it behave similarly to static RAM (SRAM). It combines the high density of DRAM with the ease of use of true SRAM.
