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RAM(Random-Access Memory)
EDO RAM (extended-data-out RAM).Despite the hype surrounding it, EDO RAM is no more than another type of FPM RAM. Essentially, it recognizes that most of the time when the CPU requests memory for a particular address, it's going to want some more addresses nearby. Instead of forcing each memory access to start afresh, EDO RAM hangs onto the location of the previous access, thereby speeding access to nearby addresses. EDO RAM speeds up the memory cycle, with improvements in memory performance of as much as 40 percent. But EDO RAM is effective only up to a bus speed of 66 MHz, and that's quickly being bypassed by the most recent crop of AMD,Cyrix, and Intel processors. DRAM (dynamic RAM).Dynamic RAM is the standard main memory type in computers today and is what you're referring to when you tell someone your PC has 32MB of RAM. In DRAM, information is stored as a series of charges in a capacitor. Within a millisecond of being electronically charged, the capacitor discharges and needs to be refreshed to retain its values. This constant refreshing is the reason for the use of the term dynamic. RAM (random-access memory).This is the umbrella term for all memory that can be read from or written to in a nonlinear fashion. However, it has come to refer specifically to chip-based memory, since all chip-based memory is random-access. It is not the opposite of ROM. The computer can read ROM; it can read and write to RAM.
SIMM (single in-line memory module).DIMM (dual in-line memory module). SIMM and DIMM refer not to memory types, but to modules (circuit boards plus chips) in which RAM is packaged. SIMMs, the older of the two, offer a data path of 32 bits. Because Pentiums are designed to handle a much wider data path than that, SIMMs must be used in pairs on Pentium motherboards (they can be used singly on boards based on 486 or slower processors). DIMMs, which are of more recent origin, offer a 64-bit path, which makes them more suitable for use with the Pentium and other more recent processors. From a buyer's standpoint, the good news is that one DIMM will handle the work of two SIMMs and thus can be used singly on a Pentium motherboard. DIMMs are more economical in the long run, because you can add one at a time to your system.
BEDO RAM (burst extended-data-out RAM).As the need for faster access to DRAM has increased, technologies have been developed to provide it. One such technology is known as bursting, in which large blocks of data are sent and processed in the form of an uninterrupted "burst" of smaller units. What this means to DRAM is that the burst carries details not only about the address of the first page, but also of the next few. BEDO RAM can handle four data elements in one burst, and this allows the final three elements to avoid experiencing the delays of the first--all the addresses are ready to be processed. The DRAM is given the first address, and then can process the rest at a rate of 10 ns each. BEDO RAM, however, despite its substantial speed increase, still has difficulty moving past the 66-MHz bus barrier. BEDO RAM exists because SDRAM manufacturers were uninterested in pricing SDRAM to be competitive with EDO RAM; as a result, more work was done with EDO to add bursting technologies for speed rivaling that of SDRAM. Hence BEDO RAM.
SDRAM (synchronous dynamic RAM).Resources galore are being poured into SDRAM development, and it has begun making its appearance in the PC ads. The reason for its increasing popularity is twofold. First, SDRAM can handle bus speeds of up to 100 MHz, and these are fast approaching. Second, SDRAM is synchronized with the system clock itself, a technical feat that has eluded PC engineers until now. SDRAM technology allows two pages of memory to be opened simultaneously. A new standard for SDRAM is being developed by the SCIzzL Association at Santa Clara University (California) along with many industry leaders. Called SLDRAM, this technology improves on SDRAM by offering a higher bus speed and by using packets (small packs of data) to take care of address requests, timing, and commands to the DRAM. The result is less reliance on improvements in DRAM chip design, and ideally a lower-cost solution for high-performance memory. Watch for SLDRAM in the near future.
SRAM (static random-access memory).The difference between SRAM and DRAM is that where DRAM must be refreshed constantly, SRAM stores data without an automatic refresh. The only time a refresh occurs, in fact, is when a write command is performed. If the write command doesn't occur, nothing in the SRAM changes, which is why it's called static. The benefit of SRAM is that it's much faster than DRAM, reaching speeds of 12 ns as compared with BEDO's 50 ns. The disadvantage is that SRAM is much more expensive than DRAM. SRAM's most common use in PCs is in the second-level cache, also called the L2 cache.22:46:56 2007-10-08 www.kurdit.5u.com