What is the difference between DDR and SDRAM?

Is 512 sd a lot different from ddr bases on performance? I have no
knowledge in this area...

Thanks
Frank

(43) writes:
Is 512 sd a lot different from ddr bases on performance? I have no
knowledge in this area...

In "the olden days" of SDRAM they had one pin on the chips that
would switch back and forth from a low voltage to a high voltage.
Every time it went from high to low that told the chips to handle
one more word of data.

Then someone got the bright idea, why not change the way the chips
were built so that they would handle one word when that pin went
from high to low and ANOTHER word when the pin went from low to
high.

Now that pin was still switching back and forth at the same rate
but there was double the data moving in the same time, i.e. double
data rate.

BUT, there are lots of other things involved in getting the chips
set up to start handling data, etc. And your cache in your CPU is
trying to make up for the processor usually being lots faster than
getting a word from memory is. So, often people only see perhaps
10% increase in speed of the system even though they have "doubled"
the speed of memory, sometimes a little more than this, sometimes
even less!

IF you had some wacky program that did almost nothing but ask for
long consecutive strings of words from memory, and never used them,
just kept asking for more and more, then you might see speeds more
like twice as fast with DDR. Fortunately almost no sane program
does this.

Then there is something completely different called "dual channel"
where it (usually) needs two identical parts installed and then the
computer tries to alternate between the two parts, while one is
busy trying to store a word the computer starts telling the other
one to store the next word, again trying to handle twice as much
data per second. But again, sub-10% gains are commonly seen with
this too. (And you can find DDR dual channel out there too, where
they try to do both of these together)

I hope this explains a little about how this stuff works

Newer motherboards ONLY use DDR, and older motherboards ONLY use SD. DDR
runs at much higher clock speeds and so is much faster in applications.
DDR2 will be on the market in a few months and will again be twice as fast
as DDR.

--
DaveW



"43" wrote in message
m...
Is 512 sd a lot different from ddr bases on performance? I have no
knowledge in this area...

Thanks
Frank