Identify Your SDRAM by the Numbers on the Chips
This is for identifying the speed of your memory modules (often called SIMMs), which is important if you're trying to figure out what speed memory you need when doing an upgrade, or refurbishing an older system. This is mainly of importance to people with older systems (built in 1998) because if your memory is PC-100 (or faster) it probably has a sticker stating its speed. Many PC-66 memory modules do not have an identifying sticker. In this case you can try to guess based on the speed of the individual memory chips.
Please note that this does not always work, because often a SIMM that is a certain speed (like 66) will use faster chips (like 100); the difference is the result of overhead imposed by the timing delays of the wiring, glue logic, or manufacturing/inventory issues. Also, in some cases it is possible for memory to be "too fast" for the system you're putting it in.
Although most of these were verified (by finding the same info at multiple web sites) I can only personally confirm the ones marked with X (which I own). O indicates ones owned by other people who have emailed me.
The third column represents the number of bits in a single package bearing the label in the first column. "Package" is the piece of plastic or ceramic with protruding metal connections; in theory a package might contain more than one "chip" but I have only known that to be true for processors and other specialized components.
To determine the size of a memory module (a small circuitboard bearing multiple packages) you need to know the number of packages on the module and the size of each package. I have indicated sizes of chips, when known, as "Mib", which is 220 bits. A "megabyte" is 8 Mib. For example, if the table shows that your memory chips are "64 Mib" chips, and you have 8 of them on a memory module, then the memory module is a 64 Megabyte module (64 M times 8 chips divided by 8 bits per byte).
Modules with 5, 9 or 18 chips have parity. They add an extra bit for each byte, which enables the hardware to instantly detect about 50% of the type of errors that would result from using incompatible memory (either too fast or too slow). When computing the size of such modules, take the size of the chip and multiply by 4 (instead of 5), by 9 (instead of 8) or by 16 (instead of 18).
|Chip's ID||Type|| size|
|5264805FTTA60||PC-100||64 Mib X|
|GM72V16821CT10K||PC-66||16 Mib X|
|HM5216805TT10H||PC-100||O CL3 SDRAM 1M x 8bit x 2bank (Daniel Lott, fr. Hitachi datasheet)|
|HY57V168010BTC-10||PC-66||16 Mib (Roy Dohmen)|
|KM4... all||see http://www.chipmunk.nl/DRAM/Samsung.htm|
|KM416S4030CT-GL||PC-100||64 Mib X|
|KM48S2020BT-G12||PC-66||16 Mib X|
|KM48S2020CT-G10||PC-66 or PC-100||16 Mib X|
|MT48LC2M8A1-10S||PC-66||16 Mib X|
|NT56V6610C0T-75S||PC-133||64 Mib O|
|P2V64S30BTP||PC-100 or PC-133|
|TC59... all||see http://www.chipmunk.nl/DRAM/Toshiba.htm|
|TC59S1608AFT-10||PC-66||16 Mib X|
|TMS... all||see http://www.chipmunk.nl/DRAM/Texas.htm|
It's interesting to note that the speed (in nanoseconds) of a memory chip does not correspond directly to the PC- bus speed. For example, PC-66 memory chips usually have 10 nanosecond speed (10 ns), but the length of a clock cycle on a 66-MHz bus is 15 nanoseconds.
It is okay to use faster RAM than your computer needs. If you need 66, it's okay to use 100. Some computer technicians have been known to erroneously tell customers that this is not true, that you must always have an exact match. They're either mistaken, ignorant and overly cautious, or deliberately trying to sell-out their older inventory.
Given what I just said, you still have to make sure not to use EDO memory in a system that needs SDRAM (for example). Also, if your computer doesn't work when you change the memory, remember there might be something broken on the motherboard or (more likely) the new memory.
ECC and Parity:
"Parity" memory detects (some) errors but does not correct errors. "ECC" memory detects errors (with far lesser risk of an undetected error) and also corrects most errors automatically. Parity memory is not used anymore these days, it has been replaced with ECC.
It used to be that you could identify Parity versus non-parity SIMMs by counting the chips (9 chips for parity SIMMs, 8 for non-parity), or other similar differences (like 5 chips instead of 4, or 10 instead of 8).
ECC memory SIMMs also have more chips, but the number of additional chips is different. Sometimes the extra chips will not all be the same type. This is because the standard way to do ECC memory is to use 13 bits to encode each byte so you'd expect to find 13 chips on an ECC SIMM --but that's not too practical. So instead you might find, for example, 6 64-Mbit chips and one 32-Mbit chip, or perhaps 7 chips of the same type, one of which is only being half-utilized.
You might be able to determine if your modules are ECC by putting them in a computer, turning on the computer and entering the BIOS setup screen. This is the screen you get by hitting Delete, F1 or some other key immediately after turning on the computer. Look around at the various BIOS screens to find the one that describes your memory size and configuration.
Most of this info comes either from merchants (wholesale dealers) and some comes from lists compiled by overclocking enthusiasts. Here are some of the web sites I found:
http://www.janpara.co.jp/ponbashi/sdram_data.htm Mon Oct 2 19:25:50 2000
Here are some individuals who sent information via email or similar means: