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SIMM and DIMM Memory Modules

The available memory on your PC will dramatically effect the speed at which your computer works. Windows, and especially Windows 95, use up memory in large quantities. For adequate Multi tasking, using Windows 95, you will need at least 16M of RAM.

The main reason that your computer appears to slow down, when running Windows with an inadequate amount of memory is its use of virtual memory to increase working space.

When running Windows assigns a working area on your hard disk called virtual memory. When it runs out of the real thing, during processing, Windows will use this area as a swap file, shifting out parts of the program and bringing it back when required.
As hard drives are so much slower than RAM, (in fact about 1.5 million times slower)it means that the processing of particular data is that much slower. The hard disk seems runs continuously when carry out a particularly complicated piece of processing.
The more memory that is added the more work Windows can do before shipping out data to the hard disk, so the faster the computer runs. If enough memory is fitted Windows will not have to move data between hard disk and computer, and run at optimum speed.

Until the end of the eighties memory came in the form of integrated circuits 'chips' of various sizes which were fitted in batches to the mother board.

The modern PC tends to use memory modules called SIMM. When fitting SIMM the gold plated connectors on the module, are pushed into its socket on the motherboard and pressed sideways into a clip which secures it.

A SIMMs Socket

SIMM's, come in 30 and 72 pin sizes the latter now becoming the standard. If you are using a 486 motherboard you may well find that you have four 30 pin and two 72 pin sockets. Older boards used 30 pin sockets. The whole situation in terms of memory cost has now changed radically. The price for 72 pin SIMMs modules have gone through the floor. 8M 72 pin EDO SIMM's are now less than £10, with the 16M version about £15 and the 32M size £28. If you still use 30 pin, their price is £10 for 4M if you can still get them.

DIMM Memory Modules

Generally, the 30 pin SIMM module was designed for 8-bit data flow, and are generally placed in groups of four to give a 32-bit data path. (4x8 = 32). This would mean that with 32 bit operation would be 4, 30 pin SIMM's at a time. Thus the 72 pin SIMM was designed for 32-pin operation, reducing the number of sockets required although this had to be off-set with a 50% increase in physical length.

To handle 64-bit operation the 72 pin SIMM would need to 'pair-up', once again, causing a space problem once more on the motherboard. One answer was the DIMM(dual in-line memory module).

Most Pentium motherboard now incorporate two, or more slots,  for a 168 pinn DIMM   module. DIMMs look similar to the older SIMM but differ in a key area. The   DIMM module uses both sides of the chip with 168 pin version having 84 pins on each side. Each pin is completely independent of the others, and makes a separate electrical contact. The density of the DIMM memory module is increased with only the slightest increase in the module’s physical size.

DIMM's also fit differently into the slot. The DIMM module is slid into 'channels' on the two edges of the socket. They are then pressed into the socket until they 'click' home.

It is a good option to purchase DIMM modules, instead of 72 pin simm, if possible. They are priced at about £25 for 32MB  and £50 for 64MB versions.