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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
(if known)
312804CT3A-260 PC-100
5264805FTTA60 PC-100 64 Mib X
81F16822B102FN PC-100
81F64842B-103FN PC-100
CSH64V0808T4 PC-100 64 Mib
D4564841G5-A10B-9JF PC-66 16 Mib
D4516821AG5-A10-7JF PC-100 64 Mib
D4564841G5-A10-9JF PC-100 64 Mib
D4564841G5-A80-9JF PC-100 64 Mib
GM72V16821BJ-16K PC-66
GM72V16821CT10K PC-66 16 Mib X
GM72V66841CT10K PC-66
GM72V66141CT-10K PC-66
GM72V16821DT-7K PC-100
GM72V661641CT7J PC-100
GM72V66841CT7J PC-100 64 Mib
GM72V66841ET7KAG5 PC-100
HM5216805TT10H PC-100 O CL3 SDRAM 1M x 8bit x 2bank (Daniel Lott, fr. Hitachi datasheet)
HM52164165TT-B60 PC-100
HM5264805TT-B60 PC-100
HM5264805CTT-B60 PC-100
HY57V168010ATC-10 PC-66
HY57V168010BTC-10 PC-66 16 Mib (Roy Dohmen)
HY57V168010CTC-10 PC-100
HY57V168010CTC-10S PC-100 16 Mib
HY57V651620ATC-10P PC-100 16 Mib
HY57V65800ALTC-10P PC-100
HY57V658020TC-10 PC-66
HY57V658020-10 PC-66
HY57V658020-11 PC-66
HY57V658020-12 PC-66
HY57V658020ATC-10S PC-100 64 Mib
HY57V658020ATC-10P PC-100
HY57V658020BTC-10P PC-100 64 Mib
HYB39S16800AT-8 PC-100 64 Mib
HYB39S16800AAT-8 PC-100
HYB39S64800AT-8 PC-100 64 Mib
HYB39S64800BT-8 PC-100
HYB39S64800CT-8 PC-100
ISGD08C2434MT PC-100
KM4... all see
KM416S4030BT-G10 PC-66
KM416S4030CT-GL PC-100 64 Mib X
KM48S2020BT-G12 PC-66 16 Mib X
KM48S2020CT-G10 PC-66 or PC-100 16 Mib X
KM48S2020CT-G8 PC-100
KM48S8030AT-F10 PC-66
KM48S8030BT-F10 PC-66
KM48S8030BT-G8 PC-100
KM48S8030BT-GH PC-100
KM48S8030BT-GL PC-100
KM48S83CT-GH PC-100
KSV884T4A1A-07 PC-133 64 Mib
M2V64S30BTO PC-100
M5M4V16S30CTP PC-66
M5M4V16S30BTP-10 PC-66
M5M4V64S30ATP-10 PC-66
M5M4V16S30DTP-8 PC-100
M5M4V64S40ATP-8 PC-100
M5M4V64S30ATP-8 PC-100
MT48LC2M8A1-10 PC-66 16 Mib
MT48LC2M8A1-10S PC-66 16 Mib X
MT48LC2M8A1-8B PC-100
MT48LC2M8A1TG-10S PC-66
MT48LC8M8A2TC-10 PC-100
MT48LC2M8A2-8E PC-100
MT48LC8MBA2-75B PC-133
MT48LC8M8A2-75C PC-133
MT48LC8M8A2-7EC PC-133
NP33S886400K-8 PC-100
NT56V6610C0T-75S PC-133 64 Mib O
P2V64S30BTP PC-100 or PC-133
PQ3S88S8 PC-133
S133K800AT-7A PC-133
SDS82V6684157-6K PC-133
SM39S64800AT-7A PC-133
TBS6408B4E-6 PC-133
TC59... all see
TC59S1608AFT-10 PC-66 16 Mib X
TC59S6404FTL-80H PC-100
TC59S6408BFT-80 PC-100 64 Mib
TC59S6408CFT-80 PC-100
TC59S6408FT-10 PC-66
TC59S6408FTL-80H PC-100
TC59S6416BFT-80 PC-100
TC59S6416FTL-80H PC-100
TM31S06584BP-7H PC-100
TMS... all see
TMS3816B4E-7 PC-100 64 Mib
TMX626812BDGE5M PC-100
TMX664814A81A7ET PC-100
TSV884T4ATA PC-100
V54C365804VBT8PC PC-100
V54C365804VCT8PC PC-100 64 Mib
VC532881FT-8 PC-100
VG3617801BT-10 PC-66 16 Mib
VG36648041BT-8H PC-100
VTMS8M8-75 PC-133
W986408BH-8H PC-100 64 Mib
W986408CH-75 PC-133


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: Mon Oct 2 19:25:50 2000

Here are some individuals who sent information via email or similar means:

Roy Dohmen

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