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Tom's Ultimate RAM Speed Tests

DDR2 Speeds

Standard nameMemory clockCycle timeI/O Bus clockData transfers per secondModule namePeak transfer rate
DDR2-400100 MHz10 ns200 MHz400 MillionPC2-32003200 MB/s
DDR2-533133 MHz7.5 ns266 MHz533 MillionPC2-4200PC2-430014266 MB/s
DDR2-667166 MHz6 ns333 MHz667 MillionPC2-5300PC2-540015333 MB/s
DDR2-800200 MHz5 ns400 MHz800 MillionPC2-64006400 MB/s
DDR2-1066266 MHz3.75 ns533 MHz1066 MillionPC2-85008533 MB/s

Source: Wikipedia

At this point, mainstream users should go for branded DDR2-800 memory. Quicker timings (low CL values) are favorable, but you shouldn’t fork out considerably more money, as the differences are small. DDR2-1066 is important for systems based on AMD Phenom processors, as their memory controllers can utilize the faster memory.

DDR3 Speeds

Standard nameMemory clockCycle timeI/O Bus clockData transfers per secondModule namePeak transfer rate
DDR3-800100 MHz10 ns400 MHz800 MillionPC3-64006400 MB/s
DDR3-1066133 MHz7.5 ns533 MHz1066 MillionPC3-85008533 MB/s
DDR3-1333166 MHz6 ns667 MHz1333 MillionPC3-1060010667 MB/s[4]
DDR3-1600200 MHz5 ns800 MHz1600 MillionPC3-1280012800 MB/s

Source: Wikipedia

At this point we recommend waiting on purchasing DDR3 memory, as most speed grades are still considerably more expensive than DDR2 RAM, without delivering better performance. Even when it comes to high capacity memory kits, you can get much cheaper deals on quad 2 GB DDR2 DIMM packages than on comparable DDR3 memory.

  • digibri
    The article mentions a couple of times that you need a 64 bit operating system to utilize 4 GB or RAM because 32 bit (XP for instance) can only access 3 GB of memory.

    1) Is it true that 32bit XP can only access 3GB? I thought it was 3.5GB...

    2) If I build a system and load it with 4GB of memory, will 32bit XP work well enough (only accessing it's 3GB or 3.5GB maximum) or will it have difficulty running properly? Meaning, is it preferable or necessary to build a 32bit XP box with only 3GB exactly?

    Great article, thanks.

    B.
    Reply
  • digibri
    The article mentions a couple of times that you need a 64 bit operating system to utilize 4 GB or RAM because 32 bit (XP for instance) can only access 3 GB of memory.

    1) Is it true that 32bit XP can only access 3GB? I thought it was 3.5GB...

    2) If I build a system and load it with 4GB of memory, will 32bit XP work well enough (only accessing it's 3GB or 3.5GB maximum) or will it have difficulty running properly? Meaning, is it preferable or necessary to build a 32bit XP box with only 3GB exactly?

    Great article, thanks.

    B.
    Reply
  • imatt
    Yes XP32 can access 3GB, but it subtracts the amount of RAM on your video card from that. So if you have 512MB or RAM on your video card, XP32 would only see 2.5GB of system RAM. I went through this last week when I upgraded to 4GB RAM, so I switched to Vista64. Gaming rig. No regrets.
    Reply
  • digibri
    How does XP64 do these days? Is there better driver support?
    Reply
  • creepster
    "More memory, meaning 4 GB, requires a 64-bit operating system..."

    Except it doesn't. 32bit Linux can use in excess of 4GB of memory, though not on all chipsets. I was looking at this issue only yesterday. I was unable to see 4GB with a motherboard using an Intel 945 chipset but on with an Intel 965 chipset I was able to see all 4GB just fine using the bigsmp kernel.
    Reply
  • sailer
    9456991 said:
    How does XP64 do these days? Is there better driver support?

    I find that XP64 does quite well. I've had it on one of my computers for a year now and have had no driver troubles. That's one thing I think Vista 64 has been for, getting the hardware companies to finally make 64 bit drivers. Also, in comparing my machine with XP64 and the one with Vista 64, the XP64 is much easier to use. Of course, the XP64 does not support gaming with DX10. I'll be building a new office machine during the next month and after using Vista 64 the past few weeks on my gaming machine, I'll install XP64 on the office machine.

    As to the article on the ram, I didn't see it answer anything new, only confirm what was already thought. One poorly written part was page 4, "How ram sensitive are different CPUs?" The following paragraph didn't seem to address the opening line at all. Even in the conclusion of the article, there was not much said to answer the question, just an allusion that memory type was was of small relevance to either of the CPUs.
    Reply
  • philbob10
    The actual amount 32-bit Windows can see without Extended Memory Addressing turned on is 3.3GB. This is a result of the OS using the addresses past the 3.3 boundary for addressing hardware, etc. Having 4GB in your system will not affect your performance.

    Linux can address more than 3.3GB and beyond with the 32-bit kernel using the same means the Windows Server variants can, by using Extended Memory Addressing, and it's support is dependent on the memory controller and BIOS, as well as the OS.
    Reply
  • hawk4031
    Well according to Microsoft's website, Vista 32-bit can now fully use 4gb of RAM without subtracting off the total memory in your computer.

    Here is the article:

    http://technet2.microsoft.com/WindowsVista/en/library/005f921e-f706-401e-abb5-eec42ea0a03e1033.mspx?mfr=true

    Scroll down to the "General Improvements and Enhancements" section. It is the second bullet point. Just thought I would point this out seeing as there is a RAM limit with 32-bit XP.
    Reply
  • drewd
    Something seems wrong with the data on page 3. Both DDR2 and DDR3 have a single clock that runs at the same speed at the I/O bus - for example, a DDR2-800 module has a 400MHz clock. What the table calls an "I/O clock" sounds more like the data strobes, which are not clocks. They also run at the same speed as the I/O bus, but are not free-running, like the clock. They only run when there are I/O operations. It looks like somebody confused CKE or CS with the clock. Either that, or there's a fundamental misunderstanding about what the "8 bit prefetch" is.
    Reply
  • 32bit operating systems can support a maximum of 4gb of ram. but you must subtract video ram and cpu cache from this total.
    Reply