What is the 16Mx8 and 32Mx4 organisation?

Recommended by Wim's BIOS...

Just a few questions about SDRAM after reading the FAQ. (I am interested in memory at the moment, so I read it, even if no-else will).

What is the 16Mx8 and 32Mx4 organisation? I don't understand this. I understand as far as 8 chip being single sided and 16 chip being double sided, and that, for example, the 440BX chipset supports 128Mbit chips meaning that I can install a max. 256MB sized module if I use a double sided (16 chip module) (which I have sucessfully done on a couple of occassions). However I don't understand 16Mx8 and 32Mx4 and where that comes into it. If this could be further explained I would greatly appreciate it.

Also, if I were to accidentally install, for example, a PC66 memory module on a 440BX board running a PII 400MHz processor, which would require PC100, could I damage the processor?

And, does anyone know of any visual way, by physically looking at a memory stick, to tell whether it is PC66, PC100 or PC133, assuming that there is no sticker. Otherwise, what would also be very helpful if someone knows of a program that could be downloaded which would check and report on the modules installed to say whether they are PC66, PC100 or PC133.

Finally, I don't understand the concept of caching RAM. Does this mean that everything in RAM has to be stored again in some kind of faster memory store, or what?


Any information from anyone on these general questions I would really appreciate. Thanks.

Thanks for moving the post - I forgot when creating it that I was basically starting a new topic under an existing thread which is against the forum rules - Sorry about that - Will be more careful of this in future. I look forward to any responses on the above queries.

[NickS]

Ritchie wrote:

What is the 16Mx8 and 32Mx4 organisation? I don't understand this. I understand as far as 8 chip being single sided and 16 chip being double sided, and that, for example, the 440BX chipset supports 128Mbit chips meaning that I can install a max. 256MB sized module if I use a double sided (16 chip module) (which I have sucessfully done on a couple of occassions). However I don't understand 16Mx8 and 32Mx4 and where that comes into it. If this could be further explained I would greatly appreciate it.

The "xN" refers to the number of data pins on the chip. The possible issue is that your BIOS and chipset need to be able to generate the addresses for the 32M, which may be beyond their capabilities, whereas making a module with x8 chips you need only to be capable of generating the addresses for 16M, although you have to do it for two banks.

Also, if I were to accidentally install, for example, a PC66 memory module on a 440BX board running a PII 400MHz processor, which would require PC100, could I damage the processor?

No.

And, does anyone know of any visual way, by physically looking at a memory stick, to tell whether it is PC66, PC100 or PC133, assuming that there is no sticker.

If it does not have a SPD chip it will be 66MHz. If it has an SPD chip you'd have to look at the individual chips to find out what their speed is, and then you'll be guessing. -8 could be PC66, or slow PC100. -6 could be PC100 or slow PC133, but it depends on the manufacturer.

Otherwise, what would also be very helpful if someone knows of a program that could be downloaded which would check and report on the modules installed to say whether they are PC66, PC100 or PC133.

I'd love that. If you look for a program which reports the SPD information, you'll turn up a few but they are very dependent on the chipset. Some work under Windows, some work under DOS, and some won't even work under DOS with some chipsets. For example, CTSPD doesn't like this laptop (or maybe Win2K) and won't report the info.

Finally, I don't understand the concept of caching RAM. Does this mean that everything in RAM has to be stored again in some kind of faster memory store, or what?

It can be. Although the SDRAM can be pretty fast (say 8 nanoseconds access time for PC100), the cache RAM will generally be faster. When the CPU calls for data (or instructions) from a certain address and it is in the cache, it's available much more quickly (fastest if it's actually on the processor chip). If there's a "miss" (data not in cache) then a "page" of data will be loaded into the cache (size of page depends on cache controller). If the data is changed by the CPU, the page must be written back to main memory. To keep track of changes requires a separate chip - the "Tag RAM"; and the size of the Tag RAM determines the amount of memory that can be served by cache; you can expand memory beyond this but it won't be cached.

[Denniss]

PC-100 usually has -8ns chips and PC-133 -7.5ns - PC-133 CL2 usually has -7ns chips
-10ns is good PC-66 ( i have two 32MB PC-66 capable of running with 112MHz CL2)

Nick and Denniss - Thanks for the explanations. Still having difficulty fully understanding but it helped.