# What are the differences between these kinds of RAM?
**URL:** https://boards.straightdope.com/t/what-are-the-differences-between-these-kinds-of-ram/417655
**Category:** Factual Questions
**Created:** [August 31, 2007, 7:21pm UTC](https://boards.straightdope.com/t/what-are-the-differences-between-these-kinds-of-ram/417655 "2007-08-31T19:21:08Z")
**Posts on this page:** 14
**Page:** 1
### Author:  [@elfkin477](https://boards.straightdope.com/u/elfkin477)
#### Post date: [August 31, 2007, 7:21pm UTC](https://boards.straightdope.com/t/what-are-the-differences-between-these-kinds-of-ram/417655/1 "2007-08-31T19:21:08Z")
I’ve installed RAM on a couple of other computers, and I’m used to looking up RAM for a computer and being told **the** kind it can use. My new computer can use three different #s, and I can’t figure out how they’re different. Google isn’t helping…
This computer can use (all NON-ECC, if that matters):
DDR2 PC2-4200
DDR2 PC2-5300
DDR2 PC2-6400
There has to be some differences amongst them in speed and/or quality, right? I assume that the higher the number, the “better” the RAM. The costs are pretty close, though (4200 and 5300 are within $5 in cost on Crucial’s website and 6400 only $30 more) which is confusing me more.
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### Author:  [@lazybratsche](https://boards.straightdope.com/u/lazybratsche)
#### Post date: [August 31, 2007, 7:27pm UTC](https://boards.straightdope.com/t/what-are-the-differences-between-these-kinds-of-ram/417655/2 "2007-08-31T19:27:28Z")
The difference is speed. However, anything faster than your computer needs will be wasted, since there isn’t any real performance gain from running memory faster than the FSB of the computer. There’s probably no need for the PC2-6400, in your case. This is assuming that your reference excludes slower memory, but includes faster stuff than necessary.
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### Author:  [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)
#### Post date: [August 31, 2007, 7:28pm UTC](https://boards.straightdope.com/t/what-are-the-differences-between-these-kinds-of-ram/417655/3 "2007-08-31T19:28:13Z")
[Peak transfer rate](http://en.wikipedia.org/wiki/DDR_SDRAM), or how fast the RAM can get data from point A to point B. In your case, the bottleneck is the motherboard, which can only go as fast as the slowest RAM listed. Faster RAM will run at the slower speed.
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### Author:  [@PatriotX](https://boards.straightdope.com/u/PatriotX)
#### Post date: [September 1, 2007, 2:21am UTC](https://boards.straightdope.com/t/what-are-the-differences-between-these-kinds-of-ram/417655/4 "2007-09-01T02:21:14Z")
[QUOTE=KneadToKnow]
… the motherboard, which can only go as fast as the slowest RAM listed. Faster RAM will run at the slower speed.
[/QUOTE]
Do you have a cite for this tidbit?
I was under the impression that compatibility meant that the mobo _could_ handle RAM @ that speed and that the FSB was the bottleneck.
**elfkin477** , check the Front Side Bus speed of your processor if possible. Regardless of what your mobo can handle, if your cpu can’t handle it, you won’t get it - the RAM will work at a slower speed that is compatible with your CPU.
The other question is how much difference does it make to you doing what you do with the machine. If you don’t push your machine’s limits, you may never notice the difference between the RAM speeds.
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### Author:  [@elfkin477](https://boards.straightdope.com/u/elfkin477)
#### Post date: [September 1, 2007, 3:30am UTC](https://boards.straightdope.com/t/what-are-the-differences-between-these-kinds-of-ram/417655/5 "2007-09-01T03:30:59Z")
Jesus, Microsoft makes trying to find out what sort of Ram it already has nearly as difficult as trying to get at state secrets. According to a program (CPU-Z) I found via a yahoo tech site, it currently uses DDR2 PC2-4200. So that’s what I ought to buy to match according to you guys. Thanks!
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### Author:  [@Sapo](https://boards.straightdope.com/u/Sapo)
#### Post date: [September 1, 2007, 12:46pm UTC](https://boards.straightdope.com/t/what-are-the-differences-between-these-kinds-of-ram/417655/6 "2007-09-01T12:46:14Z")
Trust the crucial website. Buy the slowest one. If you entered your computer model correctly, it will give you all the options you can use. Faster memory won’t mean a faster computer. Save the buck.
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### Author:  [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)
#### Post date: [September 1, 2007, 2:27pm UTC](https://boards.straightdope.com/t/what-are-the-differences-between-these-kinds-of-ram/417655/7 "2007-09-01T14:27:41Z")
[QUOTE=PatriotX]
Do you have a cite for this tidbit?
[/QUOTE]
Sorry if my use of “motherboard” too generically was confusing. I didn’t see any point in being more specific. Had the bottleneck been the CPU, I might have, but in this situation, chipset, bridge, fsb, etc., pretty much all boil down to motherboard as far as I’m concerned. Sorry to the OP if this caused a problem.
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### Author:  [@Montgomery0](https://boards.straightdope.com/u/Montgomery0)
#### Post date: [September 1, 2007, 3:57pm UTC](https://boards.straightdope.com/t/what-are-the-differences-between-these-kinds-of-ram/417655/8 "2007-09-01T15:57:15Z")
[QUOTE=Sapo]
Trust the crucial website. Buy the slowest one. If you entered your computer model correctly, it will give you all the options you can use. Faster memory won’t mean a faster computer. Save the buck.
[/QUOTE]
I just want clarification on this subject, as I often use the Crucial website whenever building a new PC, and I tend to get RAM higher than the lowest speed listed. Are you saying that the lowest speed RAM they list will run optimally on the MOBO that you give them, and that anything higher than that will be wasteful?
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### Author:  [@Sapo](https://boards.straightdope.com/u/Sapo)
#### Post date: [September 1, 2007, 4:36pm UTC](https://boards.straightdope.com/t/what-are-the-differences-between-these-kinds-of-ram/417655/9 "2007-09-01T16:36:50Z")
[QUOTE=Montgomery0]
I just want clarification on this subject, as I often use the Crucial website whenever building a new PC, and I tend to get RAM higher than the lowest speed listed. Are you saying that the lowest speed RAM they list will run optimally on the MOBO that you give them, and that anything higher than that will be wasteful?
[/QUOTE]
I will let a bigger expert come to answer this, but yes. That is what I understand. Anything under will hurt you but any of the listed is good enough for all your MOBO knows and cares. Fancier stuff is just pearls before the swine.
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### Author:  [@Windwalker](https://boards.straightdope.com/u/Windwalker)
#### Post date: [September 1, 2007, 6:56pm UTC](https://boards.straightdope.com/t/what-are-the-differences-between-these-kinds-of-ram/417655/10 "2007-09-01T18:56:40Z")
[QUOTE=Sapo]
Fancier stuff is just pearls before the swine.
[/QUOTE]
A hi-jack, but where does this expression come from? Or did you come up with it yourself?
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### Author:  [@CJJ](https://boards.straightdope.com/u/CJJ)
#### Post date: [September 1, 2007, 7:12pm UTC](https://boards.straightdope.com/t/what-are-the-differences-between-these-kinds-of-ram/417655/11 "2007-09-01T19:12:34Z")
[QUOTE=Windwalker]
A hi-jack, but where does this expression come from? Or did you come up with it yourself?
[/QUOTE]
Unless he’s the 2nd coming 🙂 , it’s from the Sermon on the Mount, Matt. 7:6.
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### Author:  [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)
#### Post date: [September 1, 2007, 7:18pm UTC](https://boards.straightdope.com/t/what-are-the-differences-between-these-kinds-of-ram/417655/12 "2007-09-01T19:18:31Z")
Are the swine in the Iraq?
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### Author:  [@Sapo](https://boards.straightdope.com/u/Sapo)
#### Post date: [September 1, 2007, 7:18pm UTC](https://boards.straightdope.com/t/what-are-the-differences-between-these-kinds-of-ram/417655/13 "2007-09-01T19:18:39Z")
[QUOTE=CJJ\*]
Unless he’s the 2nd coming 🙂 , it’s from the Sermon on the Mount, Matt. 7:6.
[/QUOTE]
I am very proud of that first time I said it.
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### Author:  [@groman](https://boards.straightdope.com/u/groman)
#### Post date: [September 1, 2007, 7:43pm UTC](https://boards.straightdope.com/t/what-are-the-differences-between-these-kinds-of-ram/417655/14 "2007-09-01T19:43:29Z")
[QUOTE=Montgomery0]
I just want clarification on this subject, as I often use the Crucial website whenever building a new PC, and I tend to get RAM higher than the lowest speed listed. Are you saying that the lowest speed RAM they list will run optimally on the MOBO that you give them, and that anything higher than that will be wasteful?
[/QUOTE]
RAM isn’t self clocked, the motherboard runs whatever RAM at whatever speed it wants. RAM typically just reports to the motherboard what speed and latencies it’s rated for, and the motherboard typically obliges.
Typically, motherboards will not have independent channels so all RAM in the system will run at the same speed. If the speed ratings are mismatched then either
a) Some ‘fast’ RAM will be running slower than it can be
b) Some ‘slow’ RAM will be running faster than it should be, possibly causing errors, instability or even refusing to POST/boot.
Now, most motherboards default to (a) since it doesn’t hurt anybody. Some motherboards will allow you to do (b) with a BIOS or jumper setting.
Now, I’m guessing that even though there’s a point of diminishing returns, it makes sense to try to get the fastest RAM your motherboard/CPU combination allows, and make sure that it’s actually running at that speed.