Datasheet

Identifying Motherboards 27
FIGURE 1.13 Single inline memory modules (SIMMs)
30-pin SIMM
72-pin SIMM
FIGURE 1.14 Dual inline memory module (DIMM)
A RIMM (Rambus inline memory module) is just like a DIMM, except it’s a Rambus
DRAM stick, has 184 pins, and is slightly longer in size.
SoDIMMs and MicroDIMMs
Portable computers (notebooks and subnotebooks) require smaller sticks of RAM because
of their smaller size. Two types are small outline DIMM (SoDIMM), which can have 72,
144, or 200 pins, and MicroDIMM, which has either 172 or 214 pins.
Parity and Nonparity RAM
Some sticks of RAM have a parity bit on them for error detection. The parity bit works by
adding up the number of 1s in a particular row of data in RAM (for example, 32-bit RAM
has 32 individual binary digits). It then adds either 1 or 0 to that total to make it come out
even. When retrieving the data from RAM, it re-adds the 1s again, and if the parity bit
doesn’t come out the same, it knows an error has occurred.
You can identify a parity SIMM by counting the number of chips on the stick. If there
are nine, it’s parity RAM. If there are eight, it’s nonparity.
When do you choose parity RAM? Usually the motherboard requires either parity
or nonparity; a few motherboards will accept either. Nowadays parity RAM is rarely
needed because advances in RAM technology have created reliable RAM that seldom
makes errors.
One type of parity RAM is error correction code (ECC). This is a now-obsolete type of
parity RAM. Most RAM today is non-ECC.
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