DDR Memory low latency; how much benefit?

[Andre Willey]

I'm still in the process of building a new PC which will be used mainly
for home/multimedia use, including video editing and audio/video
compression tasks (not much games use).

I know low latency memory is an advantage, but I'm not sure if it will
give me a noticable speed impovement for the fairly heavy extra cost
factor.

The Ram I was looking at is 2x512Mb Corair TwinX-XL PC3200 XLPT which is
DDR400, Cas2, 2-2-2-5 latency. Would this memory configuration be
significantly faster than much cheaper twin-DDR (still Cas2) options that
don't have the low 2-2-2-5 latency?

Quick machine spec is: Abit AV8 mobo, Athlon 64 3700 "San Diego" CPU (1MB
L2 cache), ATI 9800SE All-in-Wonder AGP graphics card, Vantec Ion 2 350W
PSU.


Also, on the HD front, I plan to use an existing 80MB Ultra-DMA EIDE hard
drive as the boot drive and a new DiamondMax 250MB SATA-150 drive as the
main data drive. Would my system be noticably faster if I got a newer
SATA drive for the boot drive also, or isn't there much different between
EIDE and SATA in the real world?

Thanks for anyone's help.

Kind Regards,

Andre
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Andre Willey

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[Kadaitcha Man]

Andre Willey, <[email protected]>, the empty-minded, unenthusiastic cloud of
fart gas, and cobbler, chucked:


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Please remove the letters shown in CAPITALS from my quoted email
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Done.

to contact me directly.

Oh. Now you tell me.

--

 

[stubborn]

I'm still in the process of building a new PC which will be used mainly
for home/multimedia use, including video editing and audio/video
compression tasks (not much games use).

I know low latency memory is an advantage, but I'm not sure if it will
give me a noticable speed impovement for the fairly heavy extra cost
factor.

The Ram I was looking at is 2x512Mb Corair TwinX-XL PC3200 XLPT which is
DDR400, Cas2, 2-2-2-5 latency. Would this memory configuration be
significantly faster than much cheaper twin-DDR (still Cas2) options that
don't have the low 2-2-2-5 latency?

<snip>

Generally speaking, the more computations your computer does the more
you will benefit from lower latencies. Video encoding is some of the
most intense work your computer is asked to do, so in your case it
sounds as though you would be well advised to get the fastest ram you
can afford.

 

[Andre Willey]

Generally speaking, the more computations your computer does the more
you will benefit from lower latencies. Video encoding is some of the
most intense work your computer is asked to do, so in your case it
sounds as though you would be well advised to get the fastest ram you
can afford.

Yes, thanks. That's pretty much along the lines of what I was thinking
too, I was just wondering if anyone had any empirical data on the
subject?

Kind Regards,

Andre

P.S. Looking at the rest of this thread, the trolls are out to play this
week, aren't they?

--
Andre Willey

Address edited to avoid spam. Please remove the letters shown in CAPITALS
from my quoted email address to contact me directly. Thanks!
Visit http://www.cix.co.uk/~neverland/dlp/ for the Disneyland-Paris FAQ
List.

 

[stubborn]

Yes, thanks. That's pretty much along the lines of what I was thinking
too, I was just wondering if anyone had any empirical data on the
subject?

<snip>

I don't know about empirical data but this info may help.

Here is a reply I gave to a similar question from another group:

CL2.0 = CAS-2 = Column Address Strobe 2 clock cycles

The numbers you are refering to represent the number of clock cycles
required to access or activate the various rows and columns of the RAM
modules or memory banks. But there is more to it than that and
requires you to understand just how memory works before you can decide
if super fast settings will appreciably affect the performance of your
particular setup and programs. The ability to quickly transfer large
amounts of data may not be necessary for your end use. If you have a
quality, and fast processor you will only need fast RAM modules if
your computer will be computing a lot or encoding video. For any other
application, including games, slower RAM is fine.

" Think of a clock cycle as one tick of the second hand (but generally
at a much higher speed). Computer clocks run voltage through a tiny
crystal that oscillates at a predictable speed to give a meaningful
timing method to the computer. One clock cycle doesn't necessarily
mean that the processor does one operation. Today's high-end
processors often complete more than one operation per clock cycle, and
other times, in the worst cases, it will take several clock cycles to
complete one operation."

another: http://en.wikipedia.org/wiki/Clock_frequency

one more: http://en.wikipedia.org/wiki/DDR_SDRAM

Tom's Hardware has a good primer for understanding these numbers
http://www.tomshardware.com/motherboard/20040119/

Here is a quote:
"Information is stored by first separating the memory area into rows
and columns. The capacity of the individual chips determines the
number of rows and columns per module. When several arrays are
combined, they create memory banks.

The chips are actually accessed by means of control signals such as
row address strobe (RAS), column address strobe (CAS), write enable
(WE), chip select (CS) and several additional commands (DQ).

In today's computers, a command rate is defined in BIOS - generally
1-2 cycles. This describes the amount of time it takes for the RAS to
be executed after the memory chip has been selected.

The memory controller selects the active row. But before the row will
actually become active so that the columns can be accessed, the
controller has to wait for 2-3 cycles - tRCD (RAS-to-CAS delay). Then
it sends the actual read command, which is also followed by a delay -
the CAS latency. For DDR RAM, CAS latency is 2, 2.5 or 3 cycles. Once
this time has lapsed, the data will be sent to the DQ pins. After the
data has been retrieved, the controller has to deactivate the row
again, which is done within tRP (RAS precharge time).

There is one more technical restriction - tRAS (active-to-precharge
delay). This is the fewest number of cycles that a row has to be
active before it can be deactivated again. 5-8 cycles are about
average for tRAS."