PC Memory question

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eeun's picture
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Joined: Dec 19 2003
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Oh, God...I've fallen behind in tech knowledge.

I picked up another AMD system - an XP2000+ on a cheap-o Biostar board, with DDR 2100 memory.

My question is, what does the 2100 indicate? As far as my understanding goes, the memory is only running at 266MHz - double the 133 bus speed.

Googling hasn't been too helpful, unless I want to -buy- DDR 2100.

I'm embarassed asking this. I've obviously not kept up on the PC technology for the last couple years.
:Smile

The sucker ran hot as stink when I got it home. Hitting 70C on the chip diode (knowing it's only a close guess to the real temperature...still scared me). Got that fixed, at least.

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Eudimorphodon's picture
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Mickey Mouse-ities.

Okay, when you see "PC1600", "PC2100", etc, here's the justification: (In this case, for PC2100:)

A: Clock Speed is 133Mhz.
B: It does two read cycles a clock. 266 million reads a second
C: DIMMs are 64 bits wide, so multiply by 8. That gets you a theoretical 2128 thousand million bytes per second bandwidth. (2.1 GB/s.) Round to a nice marketable number, and you get PC2100.

It's confusing, because normal SDRAM was just rated by clock speed. (I.E., a 100mhz-capable DIMM is "PC100". If you were using the same math applied to DDR that should be a "PC800" DIMM.)

Yah for the computer industry.

--Peace

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And don't even get us started

And don't even get us started on the confusing system of speed ratings AMD uses on the Athlon XP and Opteron CPU's

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eeun's picture
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Re: And don't even get us started

drbob wrote:

And don't even get us started on the confusing system of speed ratings AMD uses on the Athlon XP and Opteron CPU's

Ahhh....marketing geniuses. This thread slowly cross-references with the "heartburn medication and Fuji film" thread.

Eudi, thanks for clearing that up.

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I have had no problems with m

I have had no problems with mixing and matching various speeds of ddr ram. I stuck a 256 meg ddr pc1600 dimm into a box with pc2100 and it worked fine. (I beleive it clocks itself down to the slowest chip though).

I also stuck a 2100 ddr stick in with a faster chip on a new intel p4 motherboard and it worked fine as well.

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The Czar's picture
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RAM Is Pretty Flexible Like That

As long as the voltage and physical connector are right for the slot (don't get me started Wink ), you can install whatever RAM you want. Theoretically, you *could* install PC100 in a DDR system and it would work fine, however, latency issues would cause mass instability within the system and for the price of it, it's just not worth the headaches.

Cheers,

The Czar

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Eudimorphodon's picture
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Re: RAM Is Pretty Flexible Like That

The Czar wrote:

Theoretically, you *could* install PC100 in a DDR system and it would work fine, however, latency issues would cause mass instability within the system and for the price of it, it's just not worth the headaches.

Of course, the pinout and connector shape differs between SDRAM and DDR DIMMs, so...

--Peace