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General Information -

SDRAM ( Synchronous Dynamic Random Access Memory )

Synchronous memory is synchronized so that the clock cycle of the memory matched with the clock cycle of the bus.

It replaced the slower and older EDO memory.

There are two types of SDRAMs, the 2-clock and the 4-clock. Physically they are the same. You can not use one type when the other is needed. Check with the motherboard's documentation to find out the exact requirements.

The 2-clock SDRAM module accesses two chips on the module on each clock cycle . The 4-clock SDRAM accesses 4 chips per clock cycle. 

The most common type is the 4-clock chip.

The term "Dynamic" implies that the memory chips uses 'dynamic' refreshing to keep the data alive. This process periodically sends current to the chip, which acts like a capacitor, to prevent it from loosing the electric charge which starts to decay immediately after the refresh. The charged state of one gate is the equivalent contents of one bit of data. 

In contrast, 'static' memory only needs a steady current to be applied to the chip in order to keep the contents alive.

The term 'random access' implies that the memory can be retrieved in a random (non-sequential) manner by providing to the chip a memory address and in return the chip presents the contents of that address. A non-random (sequential method) would be equivalent to a bicycle chain, each chain being one bit. In such a system, the data can only be read after all other bits have been cycled one at a time until the required bit is presented.

If you use the wrong type your computer will not boot.

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