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Cheap Computer Memory

    There are many types of computer memory available today. Computer memory, in the old days (late 80 and early 90s), was very expensive. A 1989 computer was lucky to have two megs of RAM. I know, hard to believe. The computer memory also came on little DIP (Dual Inline Package) chips that were a bear to install. Today, computer memory is much more affordable and much easier to install.

    Check your operating system and application programs for their system requirements usually printed on the outside of the box. This is a good place to start to see what is recommended for the amount of computer memory you need. Remember, in most applications more memory will make your computer run faster. It will not help with network speed or dial-up connections to the Internet.

What Type of Memory Does Your Computer Support?
    
    Look through the manuals that came with your computer or motherboard. Included in the documentation should be a listing of the specifications for the computer memory supported. This is important because it will list exactly the type, size and number of memory modules that are supported. If your computer is a name brand system you can locate information on its memory capabilities and specifications  HERE .

      Generally, it is best to try and buy as few computer memory modules as possible for the amount of memory that you wish to install. This will increase the potential for future upgrades on the system. Thus, if you have 3 memory slots, one of which has a 256MB module in it, it would be better to buy another 256MB module to get to 512MB of total memory than to purchase two 128MB modules.

   Here are basic types of computer memory available today and how they are used. Most likely, you will only need to buy one kind of memory for your motherboard. Once you determine the type of memory you need for your system--whether you are building a new system or upgrading your current one--just click on the title in blue. Or, just CLICK HERE to go to one of the leaders in the aftermarket memory industry.

SIMM (Single In-line Memory Module)
SIMMs are used to store a single row of DRAM, EDO or BEDO chips where the module is soldered onto a PCB. One SIMM can contain several chips. When you add more memory to a computer, most likely you are adding a SIMM.

The first SIMMs transferred 8 bits of data at a time and contained 30 pins. When CPU's began to read 32-bit chunks, a wider SIMM was developed and contained 72 pins.

72 pin SIMMS are 3/4" longer than 30 pin SIMMs and have a notch in the lower middle of the PCB. 72 pin SIMMs install at a slight angle.


DIMM (Dual In-line Memory Module)
DIMMs allow the ability to have two rows of DRAM, EDO or BEDO chips. They are able to contain twice as much memory on the same size circuit board. DIMMs contain 168 pins and transfer data in 64 bit chunks.

DIMMs install straight up and down and have two notches on the bottom of the PCB.


SODIMM (Small Outline DIMM)
SODIMMs are commonly used in notebooks and are smaller than normal DIMMs. There are two types of SO DIMMs. Either 72 pins and a transfer rate of 32 bits or 144 pins with a transfer rate of 64 bits.

RDRAM - RIMM
Rambus, Inc, in conjunction with Intel has created new technology, Direct RDRAM, to increase the access speed for memory. RIMMs appeared on motherboards sometime during 1999. The in-line memory modules are called RIMMs. They have 184 pins and provide 1.6 GB per second of peak bandwidth in 16 bit chunks. As chip speed gets faster, so does the access to memory and the amount of heat produced. An aluminum sheath, called a heat spreader, covers the module to protect the chips from overheating.

DRAM (Dynamic Random Access Memory)
One of the most common types of computer memory (RAM). It can only hold data for a short period of time and must be refreshed periodically. DRAMs are measured by storage capability and access time.

Storage is rated in megabytes (8 MB, 16 MB, etc).

Access time is rated in nanoseconds (60ns, 70ns, 80ns, etc) and represents the amount of time to save or return information. With a 60ns DRAM, it would require 60 billionths of a second to save or return information. The lower the nanospeed, the faster the memory operates.

DRAM chips require two CPU wait states for each execution.

Can only execute either a read or write operation at one time.

FPM (Fast Page Mode)
At one time, this was the most common and was often just referred to as DRAM. It offered faster access to data located within the same row.

EDO (Extended Data Out)
Newer than DRAM (1995) and requires only one CPU wait state. You can gain a 10 to 15% improvement in performance with EDO memory.

BEDO (Burst Extended Data Out)
A step up from the EDO chips. It requires zero wait states and provides at least another 13 percent increase in performance.

SDRAM (Static RAM)
Introduced in late 1996, retains memory and does not require refreshing. It synchronizes itself with the timing of the CPU. It also takes advantage of interleaving and burst mode functions. SDRAM is faster and more expensive than DRAM. It comes in speeds of 66, 100, 133, 200, and 266MHz.

DDR SDRAM (Double Data Rate Synchronous DRAM)
Allows transactions on both the rising and falling edges of the clock cycle. It has a bus clock speed of 100MHz and will yield an effective data transfer rate of 200MHz.

Direct Rambus
Extraordinarily fast. By using doubled clocked provides a transfer rate up to 1.6GBs yielding a 800MHz speed over a narrow 16 bit bus.

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