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NOTE: There is a lot missing here and I don't know very much about memory. If you know something I don't, please email me and I'll add it to the page.

A computer has many different types of memory used in it. This is to optimize speed and price. Lightning fast cache memory for example is too expensive to use as main memory. To further complicate things, for the same use alone (eg. main memory or graphics memory) there are many different types of memory that can be used. This is a list of the more common types of memory avaliable:

  • FPM

    Fast Page Memory. Used as main memory on computers up to the Pentium 100MHz era. Typical speeds are 70ns and 60ns. Found also in budget video cards but in a 48ns version. The fastest access speed of FPM in CPU cycles is 5-3-3-3.

  • EDO

    Extended Data Output. 10% faster than normal FPM and typically found in 45ns, 50ns, 60ns and 70ns variants. Able to operate at motherboard speeds of up to 83MHz. The fastest access speed of EDO in CPU cycles is 5-2-2-2. EDO DRAM manufactured by Micron is considered to be the most stable and reliable.

  • BEDO

    Burst Extended Data Output. This RAM type is at present only supported by the VIA chipsets 580VP, 590VP, 680VP. The fastest access speed of BEDO in CPU cycles is 5-1-1-1

  • ECC

    Error Correcting Code memory is used mainly for mission critical network servers to prevent data loss which can occur due to errors made by the memory.

  • Pipeline Burst SRAM.

    Most commonly used in level 2 cache. Typical speeds are 4.5ns, 6ns and 8ns. In theory the 4.5ns version can operate at motherboard speeds of 200MHz!

  • VRAM

    Video RAM. For graphics cards. This is a dual ported version of FPM.

  • WRAM

    Windows RAM. First used in the Matrox Millenium graphics card, it has a performance slighly faster than that of video RAM. For graphics cards.

  • SGRAM

    Synchronous Graphics Random Access Memory. Used for video cards. It is similiar to SDRAM but can perform simple logical operations on data (like XOR) together with writing.

  • MDRAM

    Multibank Dynamic Random Access Memory is used in mainly in video cards and is faster than VRAM. Anyone know any more about this, please email me.

  • SDRAM

    Synchronous dynamic random access memory. Typically found in 6ns, 7ns, 10ns and 12ns variants. This type of memory can synchronize to the system clock and is the most ideal type of memory to use at high motherboard bus speeds of 100MHz and above. The fastest access speed of SDRAM in CPU cycles is 5-1-1-1.

  • SDRAM2 (DDR SDRAM)

    Double-Data-Rate Synchronous Dynamic Random Access Memory, supports 1.066-gigabyte transfer rates at 66-MHz bus speeds. Uses both the rising and falling edge of the clock cycle to double the bandwidth and reach speeds twice that of normal SDRAM. Expected to be in place by year 1999. DDR SDRAM will eventually be available at speeds of 250MHz (125MHz bus speed), with a transfer rate of 2.4GB/s.

  • RDRAM

    Rambus Dynamic Random Access Memory. Developed by Rambus Inc. It can transfer data at 533Mb/s per channel. RDRAM allows up to four channels on one memory controller, with a combined bandwidth of 2132Mb/s. It has a 2ns access speed and officially supports bus speeds of up to 133MHz.

  • nDRAM

    Backed by Intel and planed for release together with the Merced processor. Expected to be in place by year 2001.

    Formats of RAM modules:

  • SIP

    Come in chips. Yup! The one with little metal legs!

  • SIMM [Single In line Memory Module]

    Comes in either 30 pin or 72 pin format. 30 pin SIMMs only have a 8bit wide data path and were used in the 386 and 486 era. 72pin SIMMs are slightly longer than the 30 pin versions and have a 32bit wide data path. On Pentium (64bit) systems they have to be used in pairs of the same size and type.

  • DIMM [Dual In line Memory Module]

    A 168 pin memory module that is even longer than 72 pin SIMMs. SDRAM comes only in this format. A DIMM has a 64 bit or 72 bit (parity version) wide data path. Unlike SIMMs, it does not have to be used in pairs. When using more than 1 DIMM, all sizes of DIMMs can be mixed together.

  • soDIMM

    Low profile DIMM for laptops that has 144 pins.

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    Last modified on Wednesday, September 11, 1997