High end RAM confusion...

Hi all -

I'm looking to put together an engineering spec system for my university's solar car racing team, and have pretty much decided on all but the RAM.

Essentially, the more I read, the more confused I seem to get, leading to the following questions:

a) The system needs RAM and lots of it - like, in the 1-2GB range. Now, I'm reading that large amounts of DDR in particular have to reduce speed as you add modules, and that if you fill all the slots the board will run them at 266 MHz (dependant on the module size?) Is that how it actually works? Does the same hold for RDRAM?

b) I know that PC2700 DDR operates at 333, but am unsure about PC3200 and PC3500, because I could swear that I've seen both pegged at 400. What are the real speeds, and will I notice a difference between them.

c) Will running higher-speed memory asynchroniously with the FSB results in tangible performance gains? Say PC3200 on an Nforce board, or PC2700 on a Granite Bay?

d) Does dual channel refer to a property of the RAM, or the capability of a chipset to address two bays individually and thus "double" the bandwidth by splitting up the instructions?

I have a suspicion that the system may end up having to be Intel based due to the university's purchasing system, considering which I'll also ask for thoughts on the specs I'm considering. Please consider that the computer needs to run high end apps like CFD, solid modelling, and possibly FEA, and that I've been told that price can take a back seat to performance as a result:

CPU: Intel P4 3.06GHz w/ HT
Motherboard: (Depends on RAM choice, but likely Intel i850E based?)
RAM: ~1.5 GB (likely 1066 RDRAM?)
HDD: 2 x Maxtor 80GB 7200RPM ATA133
Video Card: ATI FireGL X1 (hopefully) or 9700PRO
DVD: Toshiba 16X
CD-R: Plextor 48X/24X/48X
NIC: 2 x DLink 10/100
Monitor: 21" Flat Viewsonic (FP Series)
OS: Win2K Pro
Power: Enermax or Antec, 400W

Any feedback would be greatly appreciated. Thanks!


*As the username implies, I'm generally in the dark*
6 answers Last reply
More about high confusion
  1. a) depends on the board. this isn't much of a problem in most situations.

    b)PC3200 is DDR400. PC3500 is DDR444. When both are asynchronous, the difference is negotiable (nearly non existant)

    c) Not really.

    d) dual channel ddr refers to the northbridge running two parralell MCH's -- both channels are used in paralell. the northbridge uses the two channels together for double the bandwidth. The nForce2 is an exception as it does not run the channels in a paralell arrangement per se, it uses them staggered. the reason for this is that they expect it to be used on a DDR266 cpu bus, so more then 2.1GBs bandwidth is rather useless! staggered channels allow for decreased latency, although not quite double the bandwidth.


    -Col.Kiwi
  2. I basically say listen to the Col. I just chime in with additional points and expanded explinations.


    Q1 - "a) The system needs RAM and lots of it - like, in the 1-2GB range. Now, I'm reading that large amounts of DDR in particular have to reduce speed as you add modules, and that if you fill all the slots the board will run them at 266 MHz (dependant on the module size?) Is that how it actually works? Does the same hold for RDRAM?"

    A1 - As the good Col. stated, this has much to go with the motherboard itself. Some boards allow for more DIMMs to run at higher speeds than others do. If you use DDR with a P4 make sure that the board can utilize 2 GB DDR400/PC3200 in two or more modules. (DDR400/PC3200 are the same thing) Most boards that have 4 DIMMs can support 4GB of memory, however they can't all run at the DDR400 signal speed.

    RDRAM on the other hand runs all at the same signal speed. However you will want to use PC1066. This tends to be more expensive. If you go with RDRAM you NEED to have them in pairs. With the Dual Channel DDR platforms, SDRAM is parallel. So it can run with one DIMM only. However RDRAM is serial, so you need two modules for it to work.


    Q2 - "b) I know that PC2700 DDR operates at 333, but am unsure about PC3200 and PC3500, because I could swear that I've seen both pegged at 400. What are the real speeds, and will I notice a difference between them."

    A2 - The good Col. is correct. Just to make sure you understand, DDR400 is actually at two bit per cycle signal running at 200MHz. The PC3200 is the name due to the bandwidth figure. SDRAM is a 64bit wide architecture.

    64 bits = 8 Bytes

    8 x 2 bits(DDR) x 200MHz = 3200 MB/s hence the name PC3200.

    I want you to be aware of two more things.

    A) Even if the board only supports Dual Channel at DDR266, the bandwidth will be 4256 MB/s. This is more than if you used a single channel board at DDR400.

    B) Having said that, if you are allowed to use a AMD XP, the extra bandwidth will help very little because the FSB (Front Side Bus) for the CPU only has the capacity of 2128MB/s of bandwidth. The FSB becomes a bottleneck. However with a P4 that is not the case.

    Those were just FYIs.


    Q3 - "c) Will running higher-speed memory asynchroniously with the FSB results in tangible performance gains? Say PC3200 on an Nforce board, or PC2700 on a Granite Bay?"

    A3 - Listen to the Col. (Enough said)


    Q4 - "d) Does dual channel refer to a property of the RAM, or the capability of a chipset to address two bays individually and thus "double" the bandwidth by splitting up the instructions?"

    A4 - Listen to the Col. again.

    As for Bandwidth results with an AMD on the Asus A7N8X nForce2 board, <A HREF="http://www.lostcircuits.com/motherboard/asus_a7n8x/8.shtml" target="_new">here is a results of the synthetic SiSoft benchmark.</A>

    If price is not an option you might want to use a PC1066 RDRAM based board with two 1GB sticks. They will most likely run really hot, so designing the system with extra cooling for the RDRAM would be a good idea. Dual DDR266 will run around the same results. The theoretical bandwidth calcs are...

    Single DDR400 = 3200 MB/s
    Dual DDR266 = 4256 MB/s
    (Granite Bay)

    Dual PC1066 RDRAM = 4264 MB/s

    These are the theoreticals, so this is where you do research on the boards themselves or you PM Crashman or have him chime in. :smile:


    <b><font color=red>Fredi</font color=red> <font color=red>Fredi</font color=red> He's our man! If he can't do it no one can!</b>
  3. You'll get slightly better performance from RDRAM. Either way, I suggest you consider ECC memory because you're dealing with very large numbers and very small fractions, and small match errors can accomulate (think of a small miscalculation growing in the same manner as you would tollerence stacking).

    <font color=blue>There are no stupid questions, only stupid people doling out faulty information based upon rumors, myths, and poor logic!</font color=blue>
  4. Appreciate the help... This has cleared up a lot.

    I guess the one question I have left is how serious the heat situation is going to be with the RDRAM if we go that way, considering that I'm not sure if our new shop is going to have air conditioning... It's either that or 2GB PC2100 on a granite bay board.

    Also not sure if I'm going to be able to build this one myself (the university may have exclusive contracts which require systems to come pre-built), which means less control over the case and cooling. In the case where I do build it myself, will the usual intake + exhaust fans, careful wiring and a dual fan PS be sufficient on 2GB of RDRAM or are special measures desirable? If so, what should I be doing?

    Thanks again

    *As the username implies, I'm generally in the dark*
  5. Standard cooling is fine, the heat problem mostly affects overclockers, not business users. Dell probably makes something reliable but impossible to work with once the warranty ends. HP actually has had some very nice business class PC's in the past, useing standard ATX architecture, of much higher quality than the consumer systems people are most familiar with.

    <font color=blue>There are no stupid questions, only stupid people doling out faulty information based upon rumors, myths, and poor logic!</font color=blue>
  6. A typical computer case now-adays comes with one exhaust fan plus the power supply fan(s). Usually they'll have room for a few more fans. At most I would recommend adding an intake fan to the front. Anything beyond that would depend on your environment.

    Of course, the more fans you add the noiser the PC runs.

    I'm assuming from your previous posts that any exclusive contracts will be with a local company and not an OEM (such as Dell or HP). If it is with an OEM then ignore the above, as OEM's will cut every corner imaginable, especially in case construction. The exception, as Crashman states, are their workstation pc's.

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