Types of Computer Memory

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There are many types of computer memory modules available. In this day and age, computers (laptops, PCs, etc.) generally do not use a single type of memory; rather, a combination of memory chips and modules are normally found in today's computers, depending on requirements and applications. The following is an overview of the types of computer memory:

SIMM (Single In-Line Memory Module) Dating back to the days of 286, 386, and 486 PCs, SIMMs are generally plug-in memory modules that are inserted into the CPU motherboard (or an extender memory board). A SIMM can be comprised of BEDO (Burst Extended Data Out Dynamic Random Access Memory), DRAM (Dynamic Random Access Memory) or EDO (Extended Data Out Dynamic Random Access Memory), with the memory chips (one or more) soldered on a PCB (printed circuit board). As mentioned above, it is the SIMM that is plugged into the CPU motherboard or memory extend card to expand the memory capability of the computer. Generally, when one is adding memory to a computer, it is in the form of a SIMM. Early SIMMs handled 8 data bits at a time in a 30-pin configuration; later, when CPUs were processing 32-bits, newer generation SIMMs were constructed in a 72-pin configuration.

DIMM (Dual In-Line Memory Module) DIMMs have two rows of DRAM, BEDO, or EDO memory chips. DIMMS allow for double the memory on the same size printed circuit board. A typical DIMM would be constructed in a 168-pin configuration and handle 64 data bits at a time.

SODIMM (Small Outline Dual In-Line Memory Module) SODIMMs are generally found in notebook computers and are smaller than standard DIMMs. In general, there are 2 types of SODIMMs � the first handling 32 data bits at a time with a 72-pin configuration, and the second handling 64 data bits with a 144-pin configuration. RIMM (Rambus In-Line Memory Module) Rambus Inc. in coordination with Intel developed a new memory technology called Direct RDRAM, with the in-line modules known as RIMMs. RIMMs have a 184-pin configuration and deliver a peak transfer rate of 1.6 Gigabytes per second (in 16 data bit segments). SORIMM (Small Outline Rambus In-Line Memory Module) SORIMMs have a similar outline as a SODIMM, but use the Rambus memory technology. Different Types of Memory Chips:

DRAM (Dynamic Random Access Memory) The most common type of computer memory. DRAMs hold data for a relatively brief period of time and need to be refreshed at regular intervals. DRAMs are measured by access time (in nanoseconds, or ns) and storage capacity (in megabytes, or MB). EDO (Extended Data Out) Memory Higher-performing memory than DRAM, with a gain in performance of roughly 10-15% over DRAM. BEDO (Burst Extended Data Out) Memory Higher-performing memory than EDO, with a gain in performance of roughly 13% over EDO. SDRAM (Static Dynamic Random Access Memory) A memory chip that retains memory and does not need refreshing. Another advantage of SDRAM is that it synchronizes with the CPU timing. Although faster than DRAM, it is also more expensive; available in speeds from 66 to 266 MHz. DDR SDRAM (Double Data Rate Synchronous Dynamic Random Access Memory) A memory integrated circuit that permits transactions on the rising as well as the falling edges of the clock cycle, with a bus clock speed of 100 MHz with a data transfer rate of 200 MHz.

OTHER MEMORY TYPES VRAM (Video Random Access Memory) VRAM is a video version of fast page mode memory and is found primarily in video accelerator cards.

Flash Memory A memory chip that is non-volatile, re-writable that functions like a combination random access memory and a hard disk drive. In the case of power being lost, data is retained in memory. Advantages of flash memory include low voltage, durability and high speed; for this reason, flash memory is used in printers, pagers, digital cameras, audio recorders and cell phones.

Shadow RAM (Random Access Memory) During the booting up of a computer, a minimal set of instructions to start the computer and video are stored in ROM (read only memory), known as BIOS (basic input output system). Since ROM normally executes slowly, Shadow RAM allows for the transfer of selected segments of the BIOS code from ROM to RAM memory (which is faster).