SDRAM versus DDR

  • Thread starter Thread starter Wayne Youngman
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Wayne Youngman

Hi,

I get roughly 300MB/s bandwidth from my PC100 2-2-2

and I get roughly 3000MB/s bandwidth from PC3200 2-5-2-2 on my new INTEL
dual-channel mobo. I can get more than 300MB/s from making a few small
adjustments to the PC3200.
 
I have got 768 MB of SDRAM (133 MHz) on my system.

If I go to a DDR mobo then how much 3200 DDR-400 would I need to
get to roughly match the performance of the SDRAM?
 
Dave said:
I have got 768 MB of SDRAM (133 MHz) on my system.

If I go to a DDR mobo then how much 3200 DDR-400 would I need to
get to roughly match the performance of the SDRAM?
Click to expand...
Not much, DDR ram is quite a bit faster than SDRam, however I would
recommend a minimum of 512MB. This isn't too terribly expensive and seems
to be enough for most everybody.
 
Dave said:
I have got 768 MB of SDRAM (133 MHz) on my system.

If I go to a DDR mobo then how much 3200 DDR-400 would I need to
get to roughly match the performance of the SDRAM?
Click to expand...

768MB


Tim
 
Not much, DDR ram is quite a bit faster than SDRam
Click to expand...

The options are RAM or swap (pagefile). If you're using swap it
doesn't matter how fast your RAM is, it matters how fast your hard
drive is. To match the performance of 768MB of any RAM you need 768MB,
or you risk swapping. That's assuming you actually use all of that
768MB of course, if you only ever use 256MB then 256MB will be fine.

There really is no answer to the OP's question. The question should be
"how much RAM do I need". If the OP needed 768MB of SDRAM they will
need 768MB of DDR, 768MB of Rambus, 768MB of core, 768MB of
super-optical-whizzbang-RAM...


Tim
 
How "much"? If you mean in MBs, more memory doesn't get you more
performance, not directly anyway, just more capacity. If you mean, how much
*performance* increase you can expect by switching, read on.

PC3200 is 200MHz (actual), 400MHz (effective). So, based purely on the
*effective* performance, PC3200 is 3x faster than your current PC133 SDR-RAM
(400 / 133 = 3). Add the possibility for dual channel support, available on
*some* mobo's, and perhaps you get another 5-10% improvement (varies quite a
bit) on a stock DDR400 setup, bringing it to about 3.3x improvement (3 x
1.10 = 3.3).

Of course, there's more to the story than simply RAM speed. Since that same
DDR memory only runs on a DDR mobo, and that mobo will require a modern CPU
from Intel or AMD, and preferrably supports a 200MHZ CPU FSB (synchronizing
the CPU FSB and RAM is ideal), the *overall* effect is a VAST improvement
compared to your current memory, esp. if you're using, say..., an old 66MHz
mobo w/ AMD K6.

HTH

Jim
 
be quick as memory has gone up this week and is set to rise again next
week.......

GaZzA
 
Gary said:
be quick as memory has gone up this week and is set to rise again next
week.......
Click to expand...

Then it is time to stop buying it, unless absolutely necessary, to
force the price down again.
 
" I have got 768 MB of SDRAM (133 MHz) on my system. If I go to a DDR mobo
then how much 3200 DDR-400 would I need to get to roughly match the
performance of the SDRAM? "


You may as well sell the SDRAM seperately at www.ebay.co.uk , pointing out
as many details and markings as possible, and then buy 2x 512MB PC3200. It
won't cost you much more than the amount your 768MB SDRAM will sell for, and
you'll be nicely set up for the immediate future.
 
You can get a ECS K7S5A PRO motherboard, it has two SDRAM 133 memory slots
and will work with up to a AMD 2600+ (266 bus speed)
A 2400/266 would be even a little cheaper

If you get DDR memory, then get 768MBs
 
I have got 768 MB of SDRAM (133 MHz) on my system.

If I go to a DDR mobo then how much 3200 DDR-400 would I need to get to
roughly match the performance of the SDRAM?
Click to expand...

Wrong question. The bandwidth doesn't depend on the amount of RAM it
depends on the type of RAM and the number of channels. A single channel
DDR system will have 3 times the bandwidth of a single channel SDRAM
system, a dual channel DDR system will have 6x the bandwidth. As for
system performance, the total amount of RAM is critical. You need enough
RAM so that you don't page to disk. Any kind of RAM is vastly faster then
any type of disk, RAM has access times measured in nanoseconds, disks are
measured in milliseconds, i.e. you are looking at a factor of a million. A
single channel DDR 3200 system has a bandwidth of 3200 MBytes/second, the
maximum transfer rate of a disk is 50-60MBytes/second. You get the idea,
if you have to fetch something off of a disk the speed of your RAM is
irrelevant. The bottom line is that you want as much RAM as you can
afford, I'd get at least 1G. If you have a large memory system your
applications will hang around in a RAM cache (at least they will in Linux,
I don't have any experience with XP but I'm sure that it does disk caching
also). Restarting an application will be almost instantaneous on a large
memory system because you won't have to fetch it from disk. In general
everything will feel faster if you have a lot of RAM.
 
"GwG" said:
Then it is time to stop buying it, unless absolutely necessary, to
force the price down again.
Click to expand...
Do you really think that home builders have any influence on the global
RAM market? Prices are going up because big PC manufacturers see a
recovery in their trade, and there isn't sufficient RAM manufacturing
capacity to cover increased demand. To an extent this suits the memory
manufacturers, because they've been living on bread and water for a year
or two now and could do with a healthier margin.
 
General Schvantzkoph said:
Wrong question. The bandwidth doesn't depend on the amount of RAM it
depends on the type of RAM and the number of channels. A single channel
DDR system will have 3 times the bandwidth of a single channel SDRAM
system
Click to expand...

Double Data Rate memory is three times faster? They missed a marketing
trick when they named that... ;-)

A single channel PC3200 (DDR, 200MHz clock) system will indeed have
three times the memory bandwidth of a single channel PC133 (SDR,
133MHz clock) system, but that's down to both the increased clock
(x1.5) and the doubled data rate (x2). More generally, all things
(clock, timings...) being equal DDR has double the bandwidth.

It was the wrong question though. But we got the right answers anyway
(except for telling the OP about dual-channel RAM, the relative
importance of matching memory and processor clocks with different CPUs
and how to measure how much RAM you need).


Tim
 
Double Data Rate memory is three times faster? They missed a marketing
trick when they named that... ;-)

A single channel PC3200 (DDR, 200MHz clock) system will indeed have
three times the memory bandwidth of a single channel PC133 (SDR,
133MHz clock) system, but that's down to both the increased clock
(x1.5) and the doubled data rate (x2). More generally, all things
(clock, timings...) being equal DDR has double the bandwidth.
Click to expand...

Thanks for adding the math, that's exactly what I meant 200MHz DDR is 3x
133Mhz SDRAM.
 
To those of you who want to know how much memory you need. Like General
Schvantzkoph said, "You need enough
RAM so that you don't page to disk." Here is how you find out how much you
really need, thats for Windows XP users. After running your big
applications, games, video editing, whatever it is that you usualy do on
your computer, Press ALT+CTRL+DEL and start your "Windows Task Manager" Go
to the PERFORMANCE tab, and on the bottom there will be 4 tables , Totals,
Commit Charge, Physical Memory, and Kernel memory. On the Physical Memory,
TOTAL is how much actual physical ram you have, (i got 1048036, which is
1GB). Than you look at the Commit Charge PEAK, and compare those too.
Basicaly TOTAL is how much ram you have, and PEAK is how much of it you use
at most. I have 1G, and my peak is 755668 (755MB) after running battlefield
vietnam. Than means if I only had 512, I'd be paging 243MB to the HardDrive.
If your PEAK exceeds your TOTAL, get more memory.
 
johny said:
To those of you who want to know how much memory you need.
Like General Schvantzkoph said, "You need enough
RAM so that you don't page to disk." Here is how you find out
how much you really need, thats for Windows XP users. After
running your big applications, games, video editing, whatever
it is that you usualy do on your computer, Press ALT+CTRL+DEL
and start your "Windows Task Manager" Go to the PERFORMANCE
tab, and on the bottom there will be 4 tables , Totals, Commit
Charge, Physical Memory, and Kernel memory. On the Physical
Memory, TOTAL is how much actual physical ram you have, (i got
1048036, which is 1GB). Than you look at the Commit Charge
PEAK, and compare those too. Basicaly TOTAL is how much ram
you have, and PEAK is how much of it you use at most. I have
1G, and my peak is 755668 (755MB) after running battlefield
vietnam. Than means if I only had 512, I'd be paging 243MB to
the HardDrive. If your PEAK exceeds your TOTAL, get more
memory.
Click to expand...


Very interesting.

Does the (peak) value for "Commit Charge" include all the memory
used by the PC. In other words, does Cimmit Charge include the
memory required for system programs (and those sorts of things) as
well as memory required to run applications?
 
Piotr Makley said:
Very interesting.

Does the (peak) value for "Commit Charge" include all the memory
used by the PC. In other words, does Cimmit Charge include the
memory required for system programs (and those sorts of things) as
well as memory required to run applications?
Click to expand...

Yes ... and when Peak eclipses Limit, you get a lovely error saying it's run
out of virtual memory and is trying to expand the pagefile, followed by lots
of disk activity and often a BSoD as it all gets ugly ;)



a
 
al said:
Yes ... and when Peak eclipses Limit, you get a lovely error
saying it's run out of virtual memory and is trying to expand
the pagefile, followed by lots of disk activity and often a
BSoD as it all gets ugly ;)
Click to expand...


Hey you! Have you been watching my PC over my shoulder.

Seriously now .. I have been getting exactly this recently. Popup
XP messages and a wholly untypical automatic reboot.

I am following the steps on http://www.aumha.org/win5/a/xpvm.htm.
 
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