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Unformatted text preview: ithout going into detail, the net effect is that an SDRAM can output the contents of its supercells at a faster rate than its asynchronous counterparts. Double Data-Rate Synchronous DRAM (DDR SDRAM). DDR SDRAM is an enhancement of SDRAM that doubles the speed of the DRAM by using both clock edges as control signals. ¯ ¯ ¯ 6.1. STORAGE TECHNOLOGIES 281 ¯ Video RAM (VRAM). Used in the frame buffers of graphics systems. VRAM is similar in spirit to FPM DRAM. Two major differences are that (1) VRAM output is produced by shifting the entire contents of the internal buffer in sequence, and (2) VRAM allows concurrent reads and writes to the memory. Thus the system can be painting the screen with the pixels in the frame buffer (reads) while concurrently writing new values for the next update (writes).
Aside: Historical popularity of DRAM technologies. Until 1995, most PC’s were built with FPM DRAMs. From 1996-1999, EDO DRAMs dominated the market while FPM DRAMs all but disappeared. SDRAMs ﬁrst appea...
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