RAM Upgrade vs. MB limits

[cosmic]

Hello,

According to manuals, Chaintech 5MTD2 (Intel 430TX chipset) & Intel BI440ZX M/Bs support at most 2 128MB DIMMs (SDRAM density 64Mbit) to achieve 256MB of RAM.

I have got a 256MB DIMM (PC133, SDRAMs density 128Mbit: 16x(16Mx8)) and it seems to work fine on both M/Bs (I'm ignoring that 430TX caches only last 64MBs): both M/Bs were not supposed to support 128Mbit SDRAMs.

Even more, 440ZX sees 320MB (more than declared 256MB!!) if I leave 64MB DIMM I had (PC100, SDRAMs density 64Mbit, single-side 8x(8x8)), while 430TX sees at most 256MB in any case.

I would like to know why it works (does SDRAM density have importance, what defines the limit of RAM a M/B can accept?), if it works, are there any disadvantages, like performance decrease ?

Similarly, MS-6163VA (VIA VT82C693 Apollo Pro Plus chipset) is supposed to achieve 768MB with 3 256MB DIMMs (128Mbit SDRAMs supported). Have anyone tried to plug-in one or two 512MB DIMMs (with 256Mbit SDRAMs)? http://www.PCGuide.com/ubb/confused.gif

Thank you!

[mjc]

Some boards have "hard" limits...they will not see it, use and may be very unstable with RAM in excess of their stated maximums. Others have "soft" limits based on what size RAM was commonly available when the board was manufactured, these boards may run stably with more than the stated max...about the only way I can tell if it actually work is to try it...the board you said see s the 320MB...that was 64MB and the 256MB sticks, right
Also you may hit caching limits that could cause a performance hit, or some other unforseen problem when exceeding the stated max. Density does play a role, some boards are very picky about it and the wrong density can caause memory errors, lack of memory (half the size of what you installed is common), or a failure to even POST.

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mjc
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Celts are the men that heaven made mad, For all their battles are merry and their songs are all sad.

[iisbob]

It's not so much the motherboard(s) that restrict your RAM ability, as it is the type of CPU you have.

It hinges on the external data bus, hence Pentium ( 80586 ) cpu's and above use a 64bit data bus, therefore you used to have to have (2) 32 bit 72 pin SIMMS to create a bank, now you can use (1) 64bit 168 pin DIMM module to create same bank-old 30pin 16 bit SIMMS required 4 sticks to create a bank of RAM. (2) on 486 CPU's since they were only 32bit buses.

Depending on your motherboard type, and the no# of addressing wires ( the wires you see-very microscopic ones at that - are what are termed "buses " ) determine the amount and speed of data that can be transferred between CPU and Memory/Peripherals.

These factors will determine what type/speed/width memory your Motherboard will support. And as you have noted, depending on manufacturer, these can vary radically. Also you have to remember that for liability causes, manufactorers always downplay the performance/capabilities of their product-in case of liability suits.





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iisbob
"Bachelors should be heavily taxed. It's not fair that some men should be happier than others."
-- Oscar Wilde

[JadedC36]

I understand it to be a 'chipset', or a motherboard limitation. That the chipset, or motherboard can only access a certain amount of memory regardless of how much you can insert. I'm not sure that seeing the memory, and using it are synonymous (but I would like to know!). Some boards have 4 168 pin DIMM's, and some only have 3, for the same memory type, and processor type. For example my board has 3 DIMM's but the manual says 512Meg maximum memory, either in 1 512Meg stick, 2 256M sticks, or 1 256, and 2 128's, and the warning is if memory=more than 512, system may hang during startup. I see a lot of different specifications for the different mobo's out there.

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Mike

[iropnman]

if you run pc-100 and pc-133 ram together youmust put the pc-133 into the first ram slot or bank o or 1 for thetwo to work together andyes it will bring the speedof the pc-133 down to 100 if you run them together