Explaining memory

[dreamer37]

512MB PC100 SDRAM DIMM 64x64 (64x4 SDRAM)

I have a customer/friend who wants me to explain what the 64x64 means, and the 64x4. . You see this type of info (something x something) when shopping for memory, and I could use help in understanding it.

[geeksRus]

Try this article from <a href="http://www.crucial.com/library/mb_vs_mb.asp" target="_blank">Crucial</a>. It does a good job of explaining things.

[dreamer37]

ok........
i can say the 64x4=256........and the 64x64-4096, but i am not sure how to explain how this gives 512mb of ram.
more help please, someone!

[xschmittyx]

[quote] i can say the 64x4=256........and the 64x64-4096, but i am not sure how to explain how this gives 512mb of ram.<hr></blockquote>

I think it is 64x4= 256. 64MB chips x 4 chips per side. 64x64=4096 is 64bits x 64bits=4096bits

8 bits=1 Byte

4096/8=512MB

[Platypus]

The finer detail of these things eludes me, but I can offer a practical understanding of what these numbers refer to, subject to correction:

In the case of the numbers you quote - 64x64 and 64x4

The first describes the structure of the module itself, SIMM or in this case DIMM, and gives the capacity in Megabits, as all memory is defined technically. The first figure is the bit depth in Megabits, the second is the bitwidth, which together give the Rows and Columns that memory is addressed in, eg the RAS and CAS timings. A DIMM is 64 bits (8 bytes) wide, unless it carries parity bits, one for each byte, so it would then be 72 bits wide. The bitwidth corresponds to the width of the data bus the module spans, so one DIMM spans the Pentium data bus, but two SIMMs are needed (as a SIMM is 32 bits wide) hence SIMMs must be fitted in pairs for a Pentium. To obtain the capacity in Megabytes, divide by the 8 bits per byte, so 64/8 = 8, then 64x8 = 512. If the specification is 64x72, this is parity or ECC memory, each byte is still 8 bits, the extra 8 bits are not used to store data but to cross check data integrity, so divide by 9 in this case to get the same memory capacity.

The key factor here is to ensure the memory controller on the motherboard has the capacity per slot to handle the DIMM, e.g. some can recognise 1G per slot, some max out at 512M.

The second figure describes the internal structure of the chips used on the module, the key factor here is the last digit, 4, which defines a hi-density chip. A larger figure, e.g. 32x8 would indicate standard density chips. The BIOS, which co-ordinates communication between the motherboard hardware, needs to be able to identify the structure correctly, so a BIOS which is not hi-density aware will incorrectly detect the size of the module. If this occurs it may be possible to correct with a BIOS upgrade. However it won't be possible to mix standard and hi-density modules, as the different internal structure can't be accommodated at the same time.

Hi-density memory can be expected to be less expensive for capacities which can use either density, but restricted to later boards which can recognise it.

There may be some useful info here:

<a href="http://www.componentauthority.com/memoryfaq1.html" target="_blank">http://www.componentauthority.com/memoryfaq1.html</a>

<a href="http://www.legacyelectronics.com/168_pin.html" target="_blank">http://www.legacyelectronics.com/168_pin.html</a>

<a href="http://www.oempcworld.bigstep.com/faq.html" target="_blank">http://www.oempcworld.bigstep.com/faq.html</a>

The last is comprehensive, but I found the links didn't work properly. You may need to scroll down manually.

[Orangeman]

Hi People,

Here is the transcript I got from Crucial on my query. The site was down last night when I tried to ask them but it was up this morning. Here is the transcript:

RAM Question

Conrad>It should be able to.
Conrad>checking
Orangeman>I have a SIS 730 Chipset Board, ECS k7SEM. Can my system take high density RAM or not?
Conrad>Hello Orangeman. How can I help you?

I don't like that word "should."

Orangeman

[geoscomp]

nothing like a firm answer, huh Orange

[Orangeman]

I know Geoscomp...

I don't like the word 'should.' It almost comes down to do I want to risk $30 and try. But the other question is would I damage my motherboard if I tried. After all the trouble I've had with this da&*mn motherboard I'm a little bit leery right now. I think I'll wait for some more posts until I am sure,

Thanks,
Orangeman

[Platypus]

Originally posted by Orangeman
After all the trouble I've had with this da&*mn motherboard

That's PCChips for ya...