4gb not bought as kit - update question

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I thought this would be overlooked if I tagged it onto the rest of my
thread from a fortnight or so back:

http://groups.google.com/group/alt.comp.hardware.homebuilt/browse_thread/thread/a16f2fdb917072a/4e369820a10b9610#4e369820a10b9610

Advice from the previous wizard would be appreciated. :-)

When I run Speccy or CPU-Z now, the Jedec readings run from 400mhz
through 333 mhz to 266 mhz instead of 400, 266 and 200 and the
apparently faulty 400, 400, 200 that showed for the unmatched sticks
that were replaced.

With the 400mhz, Jedec #3, set of numbers the Cas Latency is 6, as is
Ras to Cas and Cas precharge.  The previous 5,5,5, 18, 23 string of
numbers I'd learnt to key into my BIOS now apply to Jedec #2, 333
mhz.  Does this suggest I have RAM with a Cas Latency of 6 now instead
of 5, and that I should change the BIOS to 6,6,6, 18, 24 as per the
apparently appropriate Jedec 3 readings in Speccy and CPU-Z?  Or can I
leave these BIOS entries as 5,5,5, 18, 23, in which case am I
currently 'overclocking' this RAM, given that in the SPD readings
333mhz pertains to 5,5,5, 18, 23?  All seems stable though.  I hope
what I'm saying is as clear as a CPU-Z dump.

I am peeved slightly at the thought of possibly having a lower CL now,
if I have, but this has gone on a bit too long for me and I'll settle
with it.  Just like to know if I should alter the BIOS string of
numbers mentioned here for stability's sake or leave it.

Many thanks.

Re: 4gb not bought as kit - update question



poachedeggs wrote:
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http://groups.google.com/group/alt.comp.hardware.homebuilt/browse_thread/thread/a16f2fdb917072a/4e369820a10b9610#4e369820a10b9610
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Sounds like your memory is CAS6.

First, you start by checking the paper specification for the RAM
you got. The paper specification overrides the SPD, on enthusiast
RAM. If they promise it supports DDR2-800 CAS4 for example, then
they probably warrant that to be the case, and you'd return the
product if it didn't meet the paper specification they promised.

The SPD can contain the wrong information on purpose. "To encourage
the computer to be able to start when the memory is first plugged
in." But a customer who buys RAM, doesn't want the SPD table
to be so corrupt, as to cause the BIOS to malfunction.

If the packaging for the product, says it is DDR2-800 CAS5, then
you'd assume the SPD was set that way (looser than the value printed
on the package) so the memory can be started OK.

As it is, if you're seeing 6-6-6-18-24 in the SPD table for
DDR2-800 (400MHz), then you could have been given a higher
latency CAS6 memory product as a replacement.

The way the JEDEC tables work, is they define three consecutive
CAS points. Think of it as X, X+1, X+2 CAS entries in the table.
The frequency values do not have to be consecutive, as the frequency
value is the point at which the new CAS value applies.

The only thing that would not make sense, is a table with two 400MHz
entries, because that implies one table value is redefining the other.
You could have CAS4,5,6 and frequencies 266, 333, 400, or you
could have 266, 400, 533. But you shouldn't have 266, 400, 400, as
that doesn't make any sense (one of the table entries
is redundant in that case).

If we take CAS4,5,6 and 266, 400, 533 as an example, it means to use
CAS6 between 533 and 400. CAS5 between 400 and 266. CAS4 at 266
or a slower frequency. In the case of the "missing frequency", like
the 333 value, we know that 333 is between 400 and 266, and it would be
CAS5 at that frequency. The table is defining ranges of values.

If you use the BIOS auto setting, and somehow specify the RAM should
run at DDR2-800, then the BIOS will extract the values from the SPD
and use them. If the BIOS is brain dead (and some are), and you check
with CPUZ and see the values are not correct, you'd set them manually.

If the paper specification for the memory, has a tighter set of values
listed, then you'd set them up manually, apply the Vdimm required for
those settings, and do memtest. If the memory doesn't meet its paper
spec, then you'd return it.

*******

So the first question I'd have to ask you, is what is the new part number
for the memory, and do you have a piece of paper stating what
timing parameters and recommended voltage that it uses. If you have
absolutely no documentation at all, then you have to rely on the SPD
as your best means of setting up the memory. And then it would be
CAS6 DDR2-800.

    Paul

Re: 4gb not bought as kit - update question



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Absolutely brilliant, marvellously committed and generous response -
thanks.  Yes, no paper and not even any note on the stick itself
saying if it's CL5 or CL6.  I imagine and hope that as it seems 667
mhz RAM still seems the average given in non-custom machines, laptops
etc that with the RAM still being 800mhz it doesn't make too much
difference about the higher latency, especially as I'm not a gamer.

I think if I've followed you right the thing to do now is see how it
goes with auto settings and then if it goes a bit cranky to use the
manual settings for CL6.  To recap, that double entry for 400mhz
pertained to the sticks I sent back, or rather one of them.  The new
ones check out fine as a pair.

I don't know what the 'part number' is, but this is what's on the
sticks' container: Integral IN2T2GNXNFX and then DDR2 2GB 800mhz Non-
ECC DIMM and finally 44-80-40 D09, if anything meaningful can be
extracted from that, I imagine the longer letter/number combo is just
a serial number anyway.  This is basic35 per stick memory, probably
not what people call 'enthusiast' memory, at a guess.

Thanks again.

Re: 4gb not bought as kit - update question



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Just to add that the BIOS's RAM section is set to auto now and it does
seem to transpire to be CL6 going by Specky and CPU-Z.  My Windows
Experience Index for memory is a healthy 7.1 out of 7.9 as before, so
unless any instability crops up and isn't solved by manual settings
then made I think I can say this is resolved, unless there's anything
you would want to add or if my previous post brings you to add
something.

I suppose I do have a peripheral curiosity as to what purpose there is
for having higher latency 800mhz RAM - a requirement of some older yet
otherwise compatible motherboards or something maybe?

Cheers.

Re: 4gb not bought as kit - update question



poachedeggs wrote:

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I checked Micron (which I use as an example of a raw chip supplier), and
I can see both CAS5 and CAS6 chips. So they do make both of them.

The best DDR2-800 you can get is CAS3. But I don't see them for sale
any more. You can also find CAS4/5/6 at DDR2-800.

    Paul

Re: 4gb not bought as kit - update question



poachedeggs wrote:
Quoted text here. Click to load it

Yup, that "Integral IN2T2GNXNFX" is the part number, as you can see
here. It is DDR2-800 CAS6 memory. Go ahead and use it that way.
The thing is, if you do the arithmetic, CAS5 at DDR2-667 is going to be
roughly the same as CAS6 at DDR2-800, so there is no latency difference
measured in nanoseconds, between the two of them. But there is a
bandwidth difference, and so you'd select DDR2-800 as the operating
point, since it has higher bandwidth. The BIOS will likely select that
setting as well, barring an inability to find a divider to enable that speed.

http://www.misco.co.uk/applications/SearchTools/item-details.asp?EdpNo=339169&Tab=2&NoMapp=0

    CAS5 * 800/667 = 5.997, so CAS5 @ DDR2-667 has same latency as CAS6 @
DDR2-800

Set it to DDR2-800, if it isn't there already, and start your testing.

    Paul

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