Edward said:
It isn't worth much... as that doesn't answer my question.
There is the "theoretical bandwidth", which is used as a product
classification. So that would be the PC2100 (2100MB/sec) or
PC2700 (2700MB/sec) type number. Those number are rounded off,
to make them easy to remember, and would be 266x8 and 333x8
actual values respectively. The number 8 reflects the fact
that the DIMM is 64 bits wide or 8 bytes.
What memtest is measuring is the "actual bandwidth", and the
ratio between the two numbers is the "efficiency". The efficiency
is a function of how many gaps there are between accesses, some
of which are unavoidable in DDR. The efficiency number can
also change, whether you are using a single channel or dual
channel configuration (because the burst size of the transfers
may differ, which affects the potential efficiency). And the
efficiency differs between chipsets, from the likes of Intel,
SIS, or VIA.
In short, you need some other utility that looks at the SPD of
the DIMM. And even that is not without issues, since the internal
tables in some DIMMs do not reflect their advertised speed.
Some enthusiast memory offers PC4000, but if all you had to look
at was the contents of the SPD chip on the DIMM, it would tell
you it was a PC3200 DIMM. In the case of that enthusiast DIMM,
the user is expected to read the label, and realise that the user
has to enter the BIOS and set the memory clock manually to 500MHz.
In other words, some products do not automatically do the right
thing, speed wise.
An external label is as close as you might get, to what the
DIMM was classified as, by the seller. If the label is missing,
the SPD (which can be read by some utilities), contains
conservative speed information. In which case, you might miss
some of the potential performance of the product, if it was
an enthusiast memory.
Paul
