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I am about to buy a desktop, I narrowed it down to two choices, both are virtually identical (even in terms of price) but one has 4 GB of RAM and a 3.7 GHZ CPU the other has 8GB of RAM and a 2.7 GHZ CPU

Which is the better choice for speed?

Also as a side question, what is better:

a 2GB stick of DDR3 RAM or a 4GB stick of DDR2?

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closed as not constructive by random Mar 6 '12 at 21:38

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Will you be using a 64bit operating system? If not, then the 8Gb of RAM won't matter, as 32-bit OSes can only use 4Gb or RAM. Also if just DDR2, it wouldn't cost much to put more memory in the 3.7Ghz processor machine later –  lavamunky May 22 '10 at 21:05

5 Answers 5

up vote 9 down vote accepted

Your question as asked unfortunately has no proper answer. The only way to answer it is to do as the previous responders have done and assume a larger context.

I don't know why it is that people in general cannot grasp that computer performance can never be quantified by focusing on just one or two components. Computer performance always depends on the performance of the system as a whole.

Here are some of my thoughts as I read your question. (Many have been previously mentioned and I apologize for the repetition. It struck me it might be worthwhile to consolidate them).

  1. CPU clock speed only matters when comparing otherwise essentially identical processors. The amount of "work" performed per clock cycle is much different between, say, a Pentium 4 and a Core 2 Duo because their internal architectures are different.

    What CPUs are you comparing?

  2. The CPU to RAM throughput also is extremely important. An ostensibly faster CPU which is constantly waiting on RAM will appear to be slower. An Intel CPU with a high clock rate but an 800MHz Front Side Bus (FSB) may well run slower than a one with a lower clock rate but faster FSB.

    How fast is the connection between your CPU and your RAM in both cases?

  3. For similar reasons, the throughput between the RAM and the hard drive can also have a significant impact on system performance. This is after all why folks will pay the still exorbitant premium for a Solid State Drive (SSD). A fast CPU using a hard drive only a few years old will be slower than one using the more recent higher bit density platters.

  4. After a certain point, the amount of RAM installed is only beneficial to the extent the operating system used and the applications run are capable of effectively exploiting it. I recently increased the RAM in my Win 7 64-bit desktop from 4 to 6 GiB. I did not see any noticeable performance increase. The extra memory is most likely just not being used because of the way I use my desktop.

  5. One cannot compare DDR2 to DDR3 without any context. A naive answer to the question as you asked might be misleading depending on the full system context.

    By the way, since all recent motherboads support dual (or even triple) channel access you should never install only a single stick of RAM. Instead use match pairs. Using 2 x 1GB of DDR3 or 2 x 2GB of DDR2 will give you better performance than a single, larger stick of either RAM type.

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about the dual/triple channel bit, i've read that it doesn't actually provide significant performance increases. its just something to think about when you're planning not to far down the road to buy more ram. then you only need to add one stick instead of replace two sticks. –  wag2639 May 23 '10 at 3:21
    
I suppose like most things it depends on how heavily and in what way your apps or the OS are using memory. My personal feeling is that anything I can do that might increase RAM throughput is a direction I might as well go in. –  irrational John May 23 '10 at 17:38

Why has no one mentioned hard drive speed yet? If you're doing any heavy write-intensive operations (i.e. installing large pieces of software), it doesn't matter how fast your RAM and CPU are if you have a 5400RPM drive.

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Not so. I buy buckets of RAM, so that the system can maximally cache. If you don't touch the disk, things run at RAMming speed. And, whatever you saved by buying the slower disk is easily converted into gigabytes of cache. The other thing that really matters is defragging; I do this at 3 am on Saturdays via a cron task. – Ira Baxter 6 hours ago –  Ira Baxter May 23 '10 at 5:07
    
It is also worthwhile choosing a faster processor so that one can store files compressed on the disk and decompress them as they are read. –  Ira Baxter May 23 '10 at 21:40

Generally, more RAM has had more effect on typical desktop performance than has clock speed, but obviously it depends on how much of each is being compared. I've usually found that a 2x in clock speed feels like a decent improvement; I wouldn't expect the less than 40% increase you're describing would make a huge difference, unless you expect to be running long, compute-bound jobs, untypical of most desktop users. However, 4GB of RAM is already generous for most users' job mix, the most likely exception to this being keeping one or a couple of VMs loaded.
As a point of reference, I'm sitting in front of an older 24" iMac, 2.16 GHz dual core, 3 GB of RAM. The only time I see any slowdown is if I drag a Windows app with a large window (in a VM) quickly across its own desktop. There's enough memory for two VMs (maybe more - I haven't tried) and OS-X never gets particularly cranky. My VM's don't sit and crunch numbers though; they mostly only launch and run some interactive app or other. Another data point: With a Youtube video running in Firefox in each of OS-X and a WinXP VM, simultaneously, there's no slow down of audio or video in either context.

Bottom line: your expected job mix will determine which of those choice will be most effective for you. For most people and most job mixes, having two hands and one attention span will be limit their ability to use more or RAM than you describe.

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FSB bandwidth, if you don't have any specific applications in mind.

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As Ignacio said, it depends on what application you're doing? Are you doing video editing and processing or working with spreadsheets or playing games.

Also, the specific processor models make a difference. You can't compare in terms of raw clock cycle the performance of a AMD processor to an Intel processor or even a Core 2 Duo to a new Core i7.

However, in general more most people, I would think 4 GB of ram with 3.7 Ghz is better than 2.7 Ghz with 8 GB of RAM for pure speed. And DDR3 may be faster than DDR2 but SPECIFICS matter.

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