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Tom's Ultimate RAM Speed Tests

RAM Choices

The memory market is in the process of transitioning from DDR2 memory to the more efficient and higher density DDR3 technology; this process will be underway until the end of the year. DDR2 is available at 800 and 1066 speeds, while DDR3 reaches from 800 to 1333. Faster products are still enthusiast-class premium products, as no platform offers official support for 1600+ speeds yet.

Both technologies are based on the double data rate principle, which means that they transfer data twice per clock cycle: during the rising and falling edge of the clock signal. Each new DDR memory generation is based on smaller transistors, decreased voltage levels and higher memory density. While the internal clock speeds don’t change, the clock speed at the interface (I/O buffer) has been increasing due to an increasing level of what is called prefetch. DDR3-1600 memory works on a physical memory clock of 200 MHz, but at a prefetch of eight. The interface runs at 800 MHz, but thanks to double data rate mode, this equals a 1600 MHz frequency. DDR2-800 also runs at a 200 MHz base clock, but with a prefetch of four.

As already mentioned, performance shouldn’t be the primary reason to switch from one memory generation to the next. Memory densities, however, are more interesting. While 1 GB DIMMs (1 Gbit ICs) can be considered mainstream in the DDR2 market, DDR3 memory will be the dominant technology once 2 GB DDR3 DIMMs become affordable, and once AMD has switched to it as well, later this year.

Which Memory Should You Buy?

However, the best deals on memory can clearly be found in the DDR2 mainstream. If budget is an issue, any 2x 1 GB DDR2 brand memory kit at DDR2-800 speed will do the job perfectly well. As you will see in the benchmark section, only significantly faster (and significantly more expensive) memory can deliver a tiny performance advantage. We don’t even recommend going for DDR3 motherboards, unless you’re purchasing something in the high-end. When you’re looking at several hundred dollars for a motherboard, and similar price points for a Core 2 Quad processor and decent system components, it is acceptable to spend some more on the memory. For anyone with a limited budget, though, it’s not.

2 GB memory kits offering two DDR2-800 modules start at approximately $75, which can be considered a bargain given that 2 GB of main memory is enough to run all sorts of mainstream applications and games. More memory, meaning 4 GB, requires a 64-bit operating system, because Windows XP and Windows Vista will only be able to handle 3 GB RAM when the 32-bit versions are used. Although the 64-bit versions are equally reliable, almost equally fast, and driver support has improved a lot, be sure you double check if your devices and applications will work in a 64-bit environment.

  • 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