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 Post subject: can one put a pc3200 memory stick in a pc2700 mobo?
PostPosted: Sun Oct 31, 2004 7:24 pm 
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Joined: Sat Oct 09, 2004 9:54 am
Posts: 17
Location: Washington DC, USA
hi all,

i was wondering if anyone would know about this. i have a soyo k7vme. it can handle up to pc2700 memory but not beyond. since pc2700 memory is actually a bit more expensive than pc3200 at newegg, i would like to buy pc3200 and have the option of upgrading the mobo in the future. (i'd actually be going from pc2100 to pc3200 b/c my athlon xp 2400 chip is limited to pc2100.)

the problem is, this is obviously going against what soyo is recommending, and it would require some tweaking, i assume. the two sticks are not exactly alike:
--pc2700 is 2.5V, pc3200 is 2.6
--pc2700 'cas Latency' is 2.5, pc3200 is 3-3-3
i saw in the customer reviews at newegg that one could tinker with the latency settings, and i assume the memory is smart enough to step down to a slower speed as well. but is this (a) possible and (b) going to be fairly straightforward to do?

thanks in advance for any thoughtful advice folks can offer.

--david levy


Last edited by dglevy on Tue Nov 02, 2004 5:31 am, edited 1 time in total.

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PostPosted: Sun Oct 31, 2004 11:06 pm 
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Joined: Sun Jul 25, 2004 3:24 am
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Location: Derbyshire, England
Memory doesn't have a set speed. As with CPU's, all a particular rating means is that the stick has been certified to run correctly at (or below) that speed. The speed that the stick actually runs at in use is dermined by the frontside bus speed and memory divider. If you haven't tinkered with either of those, then if your Athlon XP2400 is running at 266MHz, any higher-rated memory you put in will do so as well. The voltage is irrelevant - if the memory is running as PC2100, then it will do fine with PC2100 voltage (in fact, it could probably run with less). Most boards autodetect the most stable latencies and run them. Just stick the memory in - the motherboard will know what to do with it. You can't damage the system by setting memory speed or latency incorrectly - at worse, it just won't boot until you get it right.

Does your board have the ability to change memory voltages and latencies manually? You probably won't have to change anything, but just in case you do....

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Last edited by Denorios on Mon Nov 01, 2004 2:12 am, edited 1 time in total.

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 Post subject:
PostPosted: Mon Nov 01, 2004 1:21 am 
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Joined: Sun Jul 25, 2004 3:24 am
Posts: 223
Location: Derbyshire, England
Have a look at this for reference

http://forums.pcper.com/showthread.php?s=&postid=2786342#post2786342

What is SPD?

SPD (Serial Presence Detect) is a feature available on all DDR modules. This feature solves compatibility problems by making it easier for the BIOS to properly configure the system to optimize your memory. The SPD device is an EEPROM (Electrically Erasable Programmable Read Only Memory) chip, located on the memory module itself that stores information about the DIMM modules' size, timings, speed, data width, voltage, and other parameters. If you configure your memory by SPD, the bios will read those parameters during the POST routine (bootup) and will automatically adjust values in the BIOS according preset module manufacturer specifications.

There is one caveat though. At times the SPD contents are not read correctly by the bios. With certain combinations of motherboard, bios, and memory setting SPD or Auto may result in the bios selecting full-fast timings (lowest possible numbers), or at times full-slow timings (highest possible numbers). This is often the culprit in situations where it appears that a particular memory module is not compatible with a given board. Often in these cases the SPD contents are not being read correctly and the bios is using faster memory timings than the module or system as a whole can boot with. In cases like these try replacing the module with another, or setting the bios to allow manual timings, and setting those timings to safer (higher) values - this will allow the combination to work.

Why are you recommending PC3500, when my motherboard only supports PC3200?

Memory modules really have no fixed speed. Like the tire to a car, there is a "rating" on it. When a tire is rated to be 150mph, it means it can run as fast as 150mph maximum. It also means that it can run at any speed lower than that. It is also quite safe to say that the tire should also withstand at 160 mph, just not as "safe" according to the Government's test environment.

Memory is very much similar in this way. Many people ask if a PC3500 or PC3700 module would run/blow up/be compatible in a motherboard originally designed to use PC3200 or PC2700. The answer is, hell ya! JEDEC (the “government”) has only approved PC3200. This reason, coupled with the fact that no processor really needs memory rated higher than PC3200, are causes for motherboard manufacturers not stating support for newer, faster modules. But higher rated speeds of DDR are always ‘backward compatible’ so to speak, or capable of running at lower speeds. Older systems stand to gain from newer and faster modules. Even if they can't run the module at its top supported frequency, you can still tweak the timing parameters to maximize performance at lower clock speeds, that otherwise would not be possible at higher clock speeds or with lower-rated modules.

Acknowledgement to Drisler at PC Perspective for writing this very useful FAQ. :)

There is a trade-off between latency and clock rate. Memory capable of high clock rates can be run at low rates with tighter timings. Low rate, tight timings can actually perform better than high rate, loose timings. In fact, there may be absolutely no difference at all between a memory stick sold as a 2-2-2-5 PC2700, and a 2.5-3-3-6 PC3200.

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 Post subject:
PostPosted: Thu Jan 25, 2007 8:11 pm 
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Joined: Sat Oct 09, 2004 9:54 am
Posts: 17
Location: Washington DC, USA
This is a 2 1/4 year late response. (How time flies!) I just wanted to thank Denorios for his kindness in taking the time to explain the intricacies of RAM speeds. I know this might seem ridiculous but my conscience was bothering me. I hate it when people fail to thank me for making the effort to help them and then I turned around and did the same thing. I'll try not to be so self-righteous the next time on the receiving end...

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AMD Athlon XP 2400+ (Thoroughbred B) CPU; Stock Heatsink; 512 MB Kingston PC2100 RAM; Soyo SY-K7VME mobo (VIA KM400 chipset); CompuCase LX-6A19 (D8000)(Thanks for the rec., Ralf!); Stock PSU (AGI [HEC] 300w.); Two Globe 120mm variable speed fans; 40 GB Seagate Hard Drive


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