The difference between PC100, PC133 and DDR memory
By Andy Walker, Cyberwalker Media Syndicate
Question: Can I mix and match some of the newer, faster memory in my
computer?
Answer: I have had a few questions along these lines lately in
various forms. Let's go over some basics and then on to innovations
in memory where I will address some frequently asked questions about
how the new RAM works.
RAM, as you may know, is Random Access Memory. It's the part of a
computer that loads programs when they are used. It is kind of a
workbench where things get done in a computer.
SDRAM or Synchronous Dynamic RAM is a kind of memory chip that was
introduced around the time that Pentium II computers appeared. If you
have one of those computers today, chances are that you are in the
market to add memory to extend the life of the computer.
Adding RAM is the best and cheapest way to stave off obsolescence in
any computer. My Pentium II 400 MHz computer, bought in early 1999,
came with 128 MB of SDRAM and I have since added two more 128 MB
SDRAM chips to the system (for about $20 US or $30 Canadian a piece!)
to give the system better performance.
SDRAM was a huge improvement on previous types of RAM because it
eliminated a lot of wait time. Traditionally the system bus (which is
all the circuitry on the motherboard that moves data around a
computer) and RAM had to wait for each other to do their part in
processing information. SDRAM changed that. Now the bus and the RAM
work at the same time. There's no tag team silliness going on.
However when you go shopping for SDRAM you'll be asked if you are
interested in PC100 or PC133 SDRAM. Without going into too much
painful detail, PC100 SDRAM is slightly slower than the PC133
version.
You can add both types to the same computer; however the machine will
default to the speed of the slowest RAM installed. If you dump your
PC100 RAM and replace it with PC133 you can take advantage of the
faster technology.
You may also have heard of DDR SDRAM. This is an even faster kind of
memory called double data rate memory. DDR memory moves data at
266MHz, but don't call it PC266 SDRAM. More about that in a minute.
To use DDR memory, your system has to specifically support the
technology. Typically PCs that run Pentium III or Pentium 4
processors that run at 1 GHz or faster will support DDR RAM, but
don't assume that all will. AMD Althon processor-based machines also
tend to support DDR SDRAM. Check with your computer maker to ensure
that the motherboard (the big uber circuit board inside your PC)
supports DDR RAM. Or look up your system on Crucial.com to find out.
When buying DDR SDRAM you'll be faced with a choice of two types.
(This is all so complicated isn't it?) They are PC1600 or PC2100.
While your motherboard may support DDR memory, you will need to check
to see that it supports PC2100 DDR SDRAM. Some early models of DDR-
enabled motherboards only work with PC1600. You also need to ensure
that the processor for your computer can support PC2100.
PC1600 DDR is designed for motherboards and processors with a 200 MHz
bus and PC2100 DDR is designed for a motherboards and processors with
a 266 MHz bus. Remember that the bus is all those circuits on the
motherboard that moves data around. They are kind of like data
highways that run between the processor and RAM and all the other
components in a computer.
Once again, a computer with a mix of PC2100 and PC1600 DDR SDRAM will
default to the slower RAM speed. If you need more info, check out
Crucial.com's amazging RAM guide. Go to Crucial.com and click the
"Library" tab for lots more useful RAM information.
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