A quick memory compatability question

[jimmyo]

Ive got an AMD Athlon 64 3200+ processor and ATI RS480 board with Radeon Xpress 200 graphics. Im looking around for some 512MB RAM for it. Is there any difference between DDR DIMM and DDR SDRAM DIMM, or is it the same??? Or, does anyone know if just both of them are compatable with my system? thanx

[PrntRhd]

RAM compatability is really important, I would suggest going to www.crucial.com and check their "configurator" to see exactly what is compatable for your system. BTW, their prices are usually reasonably competitive and they guarantee their RAM for the life of your PC.

[Orion]

PrntRhd's suggestion is probably the best way to go just get the actual RAM. As far as answering the specific question regarding the DDR SDRAM vs non specified, here goes.

The short answer is "They're the same." Understanding why, as well as being able to understand how you can answer that question yourself about similar technologies requires actually understanding the information represented by those acronyms.

The first step is in finding out what the acronyms stand for. lets start with DIMM, since that was the first technology among the ones you mentioned. DIMM stands for Dual Inline Memory Module. Explaining why this is significant is a bit of a journey through history.

Back a long while ago, memory modules had to be installed in pairs. This was because the external data width between the processor and the memory starting with the pentium was 64 bits wide. Memory modules are 32 bits wide. to use the full width, then, you needed sticks in pairs. (Just as a side note, the 486 type processors with 32 bit wide paths could use SIMMs singly) Anyways, memory modules of that type were Single inline Memory Modules, and the most common type was EDO RAM, or at least after it was introduced it was. (Historical sidestreet: EDO stands for Extended Data Out, if you're interested. Other types were FPM [Fast Page Mode] and BEDO [Burst Extended Data Out]. FPM was breifly popular, but then EDO came out just when computers got popular, and it took over in a large way. BEDO had the misfortune of coming out just before computers moved to SDRAM, so it's lifetime was really short.)

DIMMs were introduced with some rather esoteric server memory types, but was first brought into popular use when SDRAM technology came out. Essentially, DIMMs were a technology where each stick had a data path 64 bits wide, and so could accomodate the pentium's data path in single sticks. Therefore the term "DIMM" just refers to memory that is 64 bits wide. (Another Sidestreet: as many may know, the video technology SLI that is currently touted by NVidia has had several implementations in the past. someone says "This technology is good. one of it is good. double it, and it's better!" The doubling of memory bandwidth works the same way-32 bits was good, double it! Since many processors nowadays have so much bandwidth available to them, we have introduced a technology which doubles that bandwidth from 64 bits to 128 bits-that's essentially what dual channel is.)

Anyways, back to your question. This brings us to SDRAM. SDRAM stands for Synchronous Dynamic Random Access Memory. as was the case before, this was derived from a previous technology: DRAM (see the expansion of SDRAM, minus the Synchronous part). Static RAM is memory where you can go to a certain row of information randomly, and it doesn't need to be refreshed-without power, it keeps it's data for at least a little while. It's used in CPUs-that's what the CPU's cache is made of. The comparative size of SRAM to DRAM explains why there's so little cache (relatively speaking) on a processor. DRAM uses one transistor per bit, SRAM uses 3-10 or more per bit. very large. DRAM, on the other hand, is much smaller, but has to be constantly refreshed. So "DRAM", just means that is Memory that you can access at random points without scrolling sequentially through the entire memory (kind of like on a CD, you can skip to the right track-on a tape, you have to fast forward through the entire tape.) but has to be constantly reminded of what data it contains. that's the point of the latency timings that you get to play with in a good motherboard bios.

The Synchronous part refers to the fact that it is synchronized to the FSB (with the exception of the K8 core...) One cycle, one bit. (and as engineers or electricians, or just tech buffs, will tell you, a Hertz [Hz] is a cycle per second. Therefore the 100 MHz FSB equaled 100 million cycles per second, and since the amount of bits transerred equals the bit width times the cycles per second, 6.4 billion bits per second). So SDRAM simply refers to DRAM that is synchronized in some way to the FSB (or, as perfectionists may want to point out, the memory controller clock)

The bandwidth afforded by this was adaquate for a while, and then processors got too hungry... Processor companies decided that they should try sending more bits per cycle of the clock. Thus was born the last acronym you mentioned-DDR! DDR stands for Dual Data Rate. Essentially, the same thing as above-one bit per cycle is good. two per cycle is better! AMD settled on 2 bits per cycle. Effectively, that doubles the speed of the FSB. that's why your BIOS reads FSB of 200 MHz, but the processor is touting 400MHz. Intel went for even more-their "long pipelines=scalability" plan introduced in the P4 made it necessary to get even more bandwidth. They go for "Quad-Pumping" which essentially sends 4 bits per cycle. in the above example of a 200 MHz FSB, the processor would show an effective speed of 800 MHz. (bit of trivia: Most people following new tech trends at the time of the release of the P4 expected the Pentium to use a (so far) vaporware technology called QDR, or Quad Data Rate. They didn't. many again expected DDR2 to be QDR. It, again, isn't.) so DDR simply refers to the ability of the memory to transfer data at 2 bits per cycle.

That kind of defines them all. To sum up:
--DDR=memory that transfers data 2 bits per cycle.
--SDRAM=Memory that can be accessed randomly (as opposed to sequentially), but needs to be constantly refreshed and is synchronized to the Memory controller Clock.
--DIMM=Memory that is 64 bits in width.

As you can see, since the technologies kind of stack on one another; in order to be DDR, it must be SDRAM, in which case, it must be made of DIMMs.

By the way, I never have really paid attention to Intel's technologies, so I wasn't sure how Intel sends 4 bits per cycle on DDR SDRAM. I asked Saph to explain this, and he said we can work on that tomorrow. if you all are interested, we can post our results to you tomorrow.

Orion

[jimmyo]

Damn... That pretty much answered the rest of the questions a was gonna ask.
I forgot to mention that I went to the crucial memory site and found that they recommended the corsair value PC3200 RAM for my computer. I was just trying to find a local store, like Best Buy or Circuit City who carried something cheaper. They both carried Kingston brand RAM, but their chips looked different than the one in my computer. Instead of having eight "black chips" on the RAM stick, they only had four, so I figured it was a different type of RAM. But I guess I'll suck it up and spend the extra for the Corsair brand that i've found near me. Thanks for the info!

[rond36]

I forgot to mention that I went to the crucial memory site and found that they recommended the corsair value PC3200 RAM for my computer.

The ram that Crucial recommends for your PC is all made by Crucial. (http://www.crucial.com/store/listparts.asp?model=T6410&tabid=AM)

Crucial would never recommend Corsair ram!

Here is the ram Corsair recommends for your PC. (http://www.corsairmemory.com/corsair/configurator_search_results.html)

[jimmyo]

Oops... :p I don't know why I said Crucial recommended Corsair RAM. I was looking at so many brands and stores that sell my computer's RAM that I got it all mixed-up.
I ended up buying the Corsair Value RAM at Best Buy. I installed it and it seems to be working just fine. Windows starts up a lot faster and my computer doesn't slow down as bad when I open multiple progams at once.

[saphalline]

Windows starts up a lot faster and my computer doesn't slow down as bad when I open multiple progams at once.Yeah, that's one of the reasons I build my own. When I was first learning about hardware and PC stuff (so that I could play games faster :p) I was constantly running across all sorts of benchmarks and other tests on sites like tomshardware, anandtech, and arstechnica - and the RAM issue really confused me. I wondered why PC's were made with only 32-64MB of RAM when all the tests showed that 128MB or more was really the sweet spot for Win98 and Win2K, especially when it comes to gaming but also when multitasking (like you'd do in an office environment).

That's also when I started learning about system design balance. From the numerous tests and case studies on the tech sites, it seemed silly to shell out tons of money for a PIII 600 system with only 64MB of RAM. In terms of gaming performance per dollar, it was much better to have say a Celeron 466 with 192MB of RAM.

The trend continues to this day. Computers continue to be made with far less RAM than they need. I worked on a co-workers laptop earlier this year: mobile PII 333, 32MB RAM, WinXP Home. Ouch! I maxed-out her RAM to 160MB and did some tweaks and clean-ups. Boot time went from 5 minutes to 90 seconds! :eek: The extra RAM made most of the difference. I find this a lot in OEM systems, especially the laptops but also the desktops, where the RAM is the bare minimum for running the OS. 32MB for Win98? 128MB for WinXP? RAM is cheap these days, why are they still selling unbalanced systems? Marketing and money are odd things...