How do I determine the SIMM type I have?
Question
How do I determine the SIMM type I have?
Answer
Speed of SIMM
You can determine the speed of the chip by looking at the part number of each chip on the SIMM board. For example, -2, -8 and -9 are common numbers found. Look at the number that ends with a dash and a digit such as "-7". This is the rate speed or nanoseconds of the chip. With "-7" this would indicate that the memory is 70ns.
Size or capacity of SIMM
Look at the four digits to the left, these often carry information about the number of bits in the chip. A 4256 indicates 256K bits arranged in sets of four, for a total of 1Mb. "1000" indicates 1MB of bits arranged in one set.
With some memory, the last one or two digits may be changed to indicate different kinds of memory; there are 1MB chips that end with 4256, 4257, and 4258. In this case, round the last digits to an even 256 or thousand. Three-chip SIMMs will typically have two larger chips that are four times the capacity of the third chip (because 4 plus 4 plus 1 makes 9, which is the number of bits needed per byte including parity).
Parity / Non partiy
To determine if the SIMM is Parity or Non Parity, look for x36 or x9, which indicates that the chip is parity and has error checking. x36 is used with 72-pin SIMMs and x9 is for 30-pin SIMMs. If you had x32 or x8 this indicates that the chip is Non Parity or has no error checking, x32 is used with 72-pin SIMMs and x8 is used with 30-pin SIMMs.
Another maybe more easier method would be to count the total chips on the circuit board. If you see three or nine discrete chips, the SIMM probably includes a parity. If there are two or eight chips, the SIMM probably does not include parity bit. In this case, divide the number of bits by 8 to determine bytes.
Additional information
- See the SIMM definition for further information and related links.