Hey everyone. Today we’re having our first guest post, by Eric Odgen of SimplePCs.net.

Here’s a short Bio of him:
Hi, my name is Eric Ogden, I’m from Washington State and am currently a student working towards a bachelor’s degree in Computer Science. I have a love for computers and I feel that as I love them and understand them, I should share my knowledge with people who want to understand them better. Feel free to visit my site for more helpful information on computers.

Here’s his post, I hope that you enjoy it:

This is Part 1 of my super-mega-ultra-crazy-RAM guide. In Part 1 I’m going to cover the major terms that you might come across when shopping for memory, and in Part 2 I’ll cover how to go about shopping for RAM. (Mathieu: Link for part two at the end of this post)

RAM – Random Access Memory

How can you shop for RAM if you don’t even know what it is? Random Access Memory is a form of computer storage. It’s like your hard drive in your computer, but smaller and much, much faster. The part that makes it “random” is the fact that any data stored at any location can be accessed in constant time, meaning you don’t have to wait for the data to be found or for it to travel some distance to be read.

Think of it like this, you live in New York, but your friend Steve lives in L.A. You don’t want to fly all the way to L.A. because you just don’t have time in your busy schedule. If our world were like the world of computers, you could walk out your front door and instantly be in L.A. No travel time.

That’s what RAM is like, if your computer needs some piece of information it doesn’t waste time traveling to the address and getting the information, it can just get it. And no address in RAM is “closer” to its destination than another, for instance, the left side of the RAM chip isn’t read or accessed any faster than the right.

Also, your computer needs RAM to be able to even boot. Don’t think you can cut a corner here and not buy RAM, it doesn’t work like that.

DDR (1,2, & 3) SDRAM – Double Data Rate Synchronous Dynamic Random Access Memory

All you need to know about the term DDR is that this is probably the type of RAM you’ll be looking to buy for your desktop, and that it’s faster then just regular SDRAM. As for the 1,2, & 3 aspect of DDR, here’s what you need to know.

  • DDR 1
  • Standard Name

    Memory ClockData Transfers/s

    Module NamePeak Transfer Rate
    DDR-200100 MHz200 MillionPC-16001600 MB/s
    DDR-266133 MHz266 MillionPC-21002100 MB/s
    DDR-333166 MHz333 MillionPC-27002700 MB/s
    DDR-400200 MHz400 MillionPC-32003200 MB/s
  • DDR 2
  • Standard NameMemory ClockData Transfer/sModule NamePeak Transfer Rate
    DDR2-400100 MHz400 MillionPC2-32003200 MB/s
    DDR2-533133 MHz533 MillionPC2-4200

    PC2-4300

    4266 MB/s
    DDR2-667166 MHz667 MillionPC2-5300
    PC2-5400
    5333 MB/s
    DDR2-800200 MHz800 MillionPC2-64006400 MB/s
    DDR2-1066266 MHz1066 MillionPC2-8500
    PC2-8600
    8533 MB/s

    Fun fact: DDR2-667 was actually supposed to be DDR2-666 but because someone freaked out over 666, they ended raising the speed by 1 to 667.

    Note: DDR2-533/667/1066 have two Module Names listed, this is because the PC2-xxxx denotes theoretical bandwidth, usually being rounded up or down. This doesn’t really matter, though some manufacturers have used the higher bandwidth to achieve slightly higher data rates.

  • DDR 3
  • Standard NameMemory ClockData Transfers/sModule NamePeak Transfer Rate
    DDR3-800100 MHz800 MillionPC3-64006400 MB/s
    DDR3-1066133 MHz1066 MillionPC3-85008533 MB/s
    DDR3-1333166 MHz667 MillionPC3-1066710667 MB/s
    DDR3-1600200 MHz1600 MillionPC3-1280012800 MB/s

    As you can see, the memory clock of the RAM doesn’t change from DDR1 to DDR3, the speed increase comes from the input/output bus clock speed being doubled. This isn’t really relevant to shopping for RAM but it does help you understand the difference between the three speeds.

  • SO-Dimm (aka, Laptop Memory)
  • SO-DIMM memory has the same specifications as regular DDR desktop memory except for the fact that SO-DIMM is smaller. Because of it’s smaller size it’s used in laptops and net-tops (like the Mac Mini). DDR1 and DDR2 SO-DIMM modules have 200 pins, whereas DDR3 SO-DIMM has 204.
    NOTE
    : DDR1 and DDR2 SO-DIMM modules are not interchangeable, and the layout of the pins on the module prevent you from installing it into the wrong system.

  • Speed (MHz)
  • I won’t go into details here, I’ll just say that the faster the RAM, the faster your computer will be. It really is that simple. The higher the number, the faster the memory.

  • CAS/Timings/Latency
  • This is a little complex but I found a nice little chart on wikipedia that explains this all and makes it very simple to understand why the normal computing individual can ignore it.

    NOTE: Ignore Bit time and Command Rate if you don’t understand what they mean. Just note that as the technology improves, the data rate increases (good) while the bit time decreases (also good).

    TypeData rateBit timeCmd rateCycle timeCL1st word4th w.8th w.
    PC100100 MT/s10 ns100 MHz10 ns220 ns50 ns90 ns
    PC133133 MT/s7.5 ns133 MHz7.5 ns322.5 ns45 ns75 ns
    DDR-333333 MT/s3 ns166 MHz6 ns2.515 ns24 ns36 ns
    DDR-400400 MT/s2.5 ns200 MHz5 ns315 ns22.5 ns32.5 ns
    2.512.5 ns20 ns30 ns
    210 ns17.5 ns27.5 ns
    DDR2-667667 MT/s1.5 ns333 MHz3 ns515 ns19.5 ns25.5 ns
    DDR2-800800 MT/s1.25 ns400 MHz2.5 ns615 ns18.75 ns23.75 ns
    512.5 ns16.25 ns21.25 ns
    DDR3-10661066 MT/s0.94 ns533 MHz1.88 ns713.13 ns15.95 ns19.7 ns
    DDR3-13331333 MT/s0.75 ns666 MHz1.5 ns913.5 ns15.75 ns18.75 ns
    69 ns11.25 ns14.25 ns
    DDR3-13751375 MT/s0.73 ns687 MHz1.5 ns57.27 ns9.45 ns12.36 ns
    DDR3-16001600 MT/s0.625 ns800 MHz1.25 ns911.25 ns13.125 ns15.625 ns
    810 ns11.875 ns14.375 ns
    78.75 ns10.625 ns13.125 ns

    The thing to really note here is:

    1. The original seek time for the eighth word was 90 ns (nanoseconds) and now it’s down to 12.36. This is substantial.
    2. In the CS (CAS Latency) column you’ll see that for some speeds there are different values. The lower the value, the faster the seek times. That’s all you need to know.

    The thing to consider here is that with higher speed RAM (like DDR3) the lower the CAS Latency, the more you pay, and sometimes this can be quite a large sum. I would say that most people would be perfectly fine buying the higher latency RAM.

    Most of the time the lower latencies will be listed as “Performance” or “Enthusiast” RAM, so if you don’t feel too enthusiastic about your RAM performance (down to the nanosecond that is) then you probably won’t feel much of a difference with the higher latency.

  • Heat Spreaders
  • Heat spreaders are a fairly large scam in the memory world. Most computer users don’t overclock their RAM and thus, do not need heat spreaders. Many high performance RAM modules (designed for overclocking) already have at least a minor form of heat spreaders on them and anything past that isn’t necessary. If your RAM comes with them, great, but if they don’t, I wouldn’t worry too much about not purchasing them.

  • 4GB Limit
  • Windows XP (and other 32-bit operating systems) can only use 4GB’s of memory. This means 4GB’s of memory in the entire system. This includes your graphics card and any other peripherals that use even the slightest bit of memory.

    This becomes a problem if you’re still hanging on to Windows XP but want a super-duper fast graphics card. Some graphics cards now have 1GB or 1.5 GB’s of video RAM, which means that will be taken out of the total 4GB’s that XP can address.

    The answer: get a 64 bit operating system like Windows Vista x64 or Windows 7. Keep this in mind if you’re wanting lots of RAM but also wanting XP; there’s a tradeoff.

    That’s it for Part 1 of my super-mega-ultra-crazy-RAM guide, please visit my site, SimplePCs, for RAM Guide Part 2 – The Buyer’s Guide

    Mathieu: Thank you Eric for writing this guest post. Everyone, what did you think of this guest post? Give Eric some feedback and tell me: Would you like to see more in the future? Let me know.