Okay, I could use a little help from people that understand the whole memory specifications.

I managed to figure out that PC 3200U and PC2 3200U are not the same. They have different pins. Can someone explain the difference?

Also, I am rebuilding a Dell Optiplex 280 desktop with a P4 3.4 CPU. It currently has two 256 sticks of PC2 3200U Ram. I inserted 2 sticks of PC2 5300U RAM. Seems to work fine. I noticed that the 3200 speed is 400 mghz, and the 5300 shows up as a 566 speed. Since the CPU bus is 800, should I only be using the the 3200 RAM? or can I see a gain, or at least the same performance out of the 5300 RAM. I have two gigs of the 5300 RAM.

Thanks in advance for all your help.

Z-man

This site may help you get correct board for your particular computer.

From experience I do know the clock speed must be correct or the computer won't boot up. (That's what happened to mine anyway.)

PC-3200 properly known as DDR-400.
PC2-3200 known as DDR2-400
The number after PC refers to theoretical bandwidth. The number after DDR refers to the memory clock (or less accurately, speed). DDR means Double Data Rate, that is for every clock cycle there are 2 data transfers, so DDR with a 200Mhz memory clock would have a 400Mhz "speed". So it is refered as DDR-400. DDR2 does 4 data transfers per cycle, so theoretically can move twice as much data at a given latency. The doubling of data operations/cycle necessitates the different pinout.

There are respected experts that insist you get a performance edge by using even multiples - such as 3.2 gig CPU, 800Mhz bus, 400Mhz RAM, etc and they do have a point and several tests to back them up. I don't know the difference in everyday business computing. In home computing, maybe it makes more sense, because believe it or not the average home PC is taxed much more than a work PC because of all the multimedia, streaming, graphical games etc.

see this page: https://www.crucial.com/support/help.aspx?tabid=sc1

Tantivy beat me to it. We use Crucial a LOT, and their spec system is usually right on the mark.

just to follow up on what I found out here and other places. RAM seems to be backwards compatable, provided is it the same type...SDRAM, DDR, DDR II.... You can use a faster RAM in a slower machine and the RAM will just clock to the slower speed. In my case, I had RAM at 533 mghz, and put it in a machine designed to use 400 mghz. It runs just fine, but clocks at 400 mghz. In some cases in might not matter, like with 100 SDRAM and 133 SDRAM. I know these are basically the same and will run in any machine designed for either. The 133 just gives you a performance boost.

I've used just about everyone's ram. All I can tell you is that the better stuff operates at lower voltages. Other then that it can be a crap shoot even with reputable ram. Lately I've been using memory made by a company called G.Skill which is essentially rebranded micron memory (Crucial uses Micron chips). Well technically I guess Crucial is the consumer division of Micron. Anyhow, the G.Skill memory works good, uses low-voltage, runs as advertised, includes heat spreader, hasn't failed me yet, and is on average 20-25% less.

I used to be an avid Corsair fan but the last few years their QC went to crap. They also started playing the bait and switch game. They would submit "special" versions of their "production" memory to sites for review, but when you actually bought the retail version nothing would add up right.

Kingston is probably the defacto standard in "Just Memory". Meaning it's usually stable but doesn't do much in the way of performance or anything like that. Alot of OEM's use Kingston and relabel it. Supply is steady and consistent and stability is usually good.

Crucial is usually good stuff but I find their supply to be somewhat finicky. I've ran into situations where this week they have memory, next they dont, week after that they do. The memory itself is usually very high quality, produces less heat, runs at lower voltages, and responds well to performance demands.

As far as your memory they all have it nailed. PC2-3200 is DDR2-400 in general memory terms. I'd probably recommend you buy DDR2-667 as it's a higher-volume memory which means you can get it for less.

I try and get Samsung or Micron Factory Originals when possible.

Memory is like laptops... theres really only a handful of actual manufacturers, and Samsung and Micron are two of them. alot of the big OEMs, Dell etc. rebrand samsung often. They're very reliable when you get em 'straight from the factory'

I did some work with a memory wholesaler and the sales guys were always happy to get Micron and Samsung cause they're good chips at a low price.

as stated above Crucial gets alot of really good memory (including Micron) but it's hit or miss as far as whats in stock. I just ordered 4 GB of DDR2/667 for about a $100.

That's pretty much true. Actually it depends greatly on the chip and the motherboard.
Newer boards don't care as much, but the DDR and SDRAM boards did.
Depending on the board, if you mix frequencies i.e. you have one stick of 100 and one 133 the 133 chip will step down to 100. These chips are (or were) commonly labeled PC100/133 meaning that they were built to do this..whereas chips labeled PC133 would only run (stable) at that frequency.
Like I say it's not really an issue now except that RAM is so cheap it's kinda silly to buy different frequencies.