The meaning of SIMM, DIMM and the number of pins

The meaning of SIMM, DIMM and the number of pins :

Your processor communicates to the memory and add on cards through a set of parallel channels in a bus. The number it bits in the bus is merely the number of channels present. For example, motherboards using the Triton-II (430HX) and the Natoma (440FX) have a 64 bit memory bus (connecting the processor to the cache and the cache to the memory) and a 32-bit PCI bus (connecting to the add on cards). The wider the bus (i.e. the more bits) the more data that can travel per cycle thus the faster the data transfer. The data transfer rate is the width of the bus in bits times the number of transfers per second in megahertz times the data size. However, if you have a 64-bit bus you must access your memory 64- bits at a time. Each SIMM is only 32-bits wide so you must install them in pairs to get the full 64-bits. Then two SIMM's are accessed as one logical bank of RAM. Older boards that accept a single SIMM are have only a 32-bit memory bus and this reduces speed by half. There is also a small advantage to using two banks or four SIMM's of the same size.

SIMM's connect to the motherboard bus via 72 Gold or Tin (Palladium Nickel) leads. Indeed SIMM's are called Single In-line Memory Modules because that have 72 pins in a single row of in- line leads. Older SIMM's had 30-pins. Other Memory modules such as DIMM (Dual In-line Memory Modules) have all 64-bits (on 128-pins) in one set of leads so you only need to install one DIMM per bank.

Nearly 99% of motherboards use Tin (Palladium Nickel) which can plate onto the noble Gold of SIMM's in a cathode-anode reaction. According to semi- conductor corrosion specialists the amount of corrosion possible can not effect the proper function of the SIMM's because of the small contact surface. If it was true the finest SIMM makers like NEC would stop production of GOLD SIMM's immediately. Indeed, Tin is a little harder to work with because it tarnishes faster. Most engineers who design SIMM's agree that gold is the best. Only Intel has claimed otherwise. Indeed, no such cases of corrosion have been reported.

www.oempcworld.com