UH, It has to do with Parity and Non-Parity computers.
If you put a non parity memory module in a parity computer you will get less the memory than with a parity computer (not sure on this btw
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EDIT: From my aries curriculum
quote:
DIMMs and 72-pin SIMMs have a module designation consisting of words and numbers. For instance, a 72-pin "8x32" DIMM can make eight million, 32-bit strings of memory available to a computer. A 168-pin "16x64" DIMM can make 16 million, 64-bit memory strings available to a computer.
To determine a module's memory capacity, perform the following calculation.
First, determine whether your computer is parity or non-parity. A non-parity computer will use the number 8 as a divisor, while a parity computer will use the number 9 as a divisor.
Second, using the module's number of bits as the dividend, divide the dividend by either 8 or 9 (divide by 9 if your computer is parity, by 8 if your computer is non-parity.)
Third, multiply the quotient by the module's first number.
The answer is the module's memory capacity. Following are two examples:
A 72-pin 32x36 SIMM with parity.
First, the computer is parity. divisor=9
Second, divide the module's number of bits by 9. 36/9 = 4
Third, multiply the quotient by the module's first number. 4 x 32 = 128MB
Module capacity: 128MB
A 168-pin 32x64 DIMM, non-parity.
First, the computer is non-parity. divisor = 8
Second, divide the module's number of bits by 8. 64/8 = 8
Third, multiply the quotient by the module's first number. 8 x 32 = 256MB
Module capacity: 256MB