How much does dual channel matter?

duvet77

duvet77

duvet77

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How much difference to performance does dual channel memory actually make? sorry if thats a really basic question but I'm a bit simple when i comes to stuff like this?

The reason I ask is I want to stick 4gb in my computer but I'm reading that windows XP 32 bit will only recognise 3 - 3.5gb.

So I was thinking I could just stick 3gb in but that wouldn't be dual channel as my mobo requires all 4 dimms (or just 2 dimms) to be the same for dual channel... or at least I think it does.

So I could put in 2gb of dual channel or 3gb single channel. Which would be better?
 
XP (and all 32 bit OS i've learnt today) have trouble recognising the full 4GB.

DUal channel increass the bandwith but not the speed of the RAM which is totally different but since even the stnard frequencies are far from being utilised to their full, doubling the frequency is a bit of an overkill.
 
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so why does dual channel work better with Intel rather than AMD, is it to do with the way the processors receive the data?

in my case having the extra memory is going to outweigh the performance hit of not being dual channel?

is it worth asking why xp 32 can't recognise 4gb?! :confused:
 
duvet77 said:
so why does dual channel work better with Intel rather than AMD, is it to do with the way the processors receive the data?

in my case having the extra memory is going to outweigh the performance hit of not being dual channel?

is it worth asking why xp 32 can't recognise 4gb?! :confused:
Click to expand...

Dual channel doubles the available memory bandwidth, and some processor designs take advantage of memory bandwidth more than others. The classic example is the Pentium 4. Its execution pipeline has lots of stages, which means lots of memory bandwidth is handy to keep it full of data, especially when the chip mispredicts which instruction's coming next and needs to pull fresh data from RAM. On the other hand the A64 and the C2D, which is loosely based on the Pentium III, have many fewer execution stages (12-14 vs. 30ish) so memory bandwidth is less important. But with multi-core chips it's coming back into the picture again; a dual-core chip will probably make more use of high bandwidth than a single-core, and with quad-core CPUs it's becoming more and more important.

What's best for you depends on how much RAM you regularly use. If you often use more than 2GB then 3GB in single-channel would be better. But it might be that you hardly ever go over 2GB, in which case it could be a waste. What do you mainly use the PC for?

As for your other question - XP32 can only address 4GB of memory in total because it's a limitation of a 32-bit addressing system. But it reserves some of this memory space for things like your graphics card memory, etc. So the addressable RAM varies but is always less than 4GB, usually about 3.2-3.3.

Hope this helps :)
 
thanks for that Mattus... i'm slowly beginning to get my head round it.

I mainly use my computer for games... football manager at the moment, but I like to play a lot of FPS, Half Life 2, FEAR, etc and would like to be able to play Crysis when it's released.

I also do a bit of 3DS max/V ray rendering now and again.
 
Football Manager and HL2 won't need more than 2GB and I doubt FEAR will. But Crysis could well benefit from it. As for rendering, it will probably use all the RAM you can throw at it!
 
I might go for a dual channel 2gb kit for now and see how i get on. i'll hang on to my two 512 dimms and if i ever need to use them i'll stick them in too.

I've seen these kits which are reasonably priced (i've learnt not to mention prices though!):

Geil Value 2Gb PC3200 Dual Chan DDR memory kit (2x1GB) (Cas 3 8-4-4) +Aluminium heat spreader

OCZ 2GB Kit (2x1024) Platinum Series DDR PC3200 400MHz Dual Channel Memory Enhanced Latency And Platinum Heatspreader

should I bother with something like that or just go cheaps as chips?

my system is:

Athlon 64 4000+
Asrock dual sata2 motherboard (the one with agp and pci-e)
Radeon XT800GTO (soon to be X1950pro or XT)

thanks
 
More than 2GB in XP /Vista 32bit is of dubious benifit anyway. 32bit windows has two different limitations.

Whenever an application requests memory, XP assigns up to a maximum of 2GB of memory. So even if you have 3.5Gbs installed and recognised, a single application will only ever see a max 2GB.

If your heavily multitasking then this isnt likely to be a problem, as it would only take two programs both needing 2GB to send you to swap. But if your just gaming, then honestly there is very little to gain.

A few programs (I believe Microsoft SQL server is one example of a very rare type of program) can use memory in a totally different way called PAE. XP Pro supports a limited subset of PAE (capped at <4gb), while some versions of Windows 2000/2003 server actually allow considerably more PAE even with a 32bit system. Odds are, the average users has zero programs that have direct PAE support, and are thus limited to 2GB 'userspace' memory that XP 32 supplies.

Moving up to XP64, or Vista64, those limits are removed entirely for 64 bit applications. However I believe 32bit apps are still limited to 2GB userspace.

64bit windows do tend to use a bit more memory for themselves though, so 4GB is ideal, as that ensures there is always a full 2GB to give to userspace applications.
 
This is all very interesting, I'm using vista32 atm & used to have 2gig RAM but when I put a 2gig texture pack into Stalker I got a lot of swapfile action, so I got another 2gig RAM & the game runs a lot better now. I presume the extra textures are now being stored in RAM.

I expect Crysis to use a lot of textures too.

I have a total of 3584mb RAM available and after booting vista32 nabs 900mb RAM for itself as I have it caching into my bountifull supply of RAM, leaving 2684mb for whatever. Think I may take the plunge into 64bit though & have another half gig available.
 
duvet77 said:
so why does dual channel work better with Intel rather than AMD, is it to do with the way the processors receive the data?

in my case having the extra memory is going to outweigh the performance hit of not being dual channel?

is it worth asking why xp 32 can't recognise 4gb?! :confused:
Click to expand...

XP is limated to 4Gb cause it cant address any more memory locations. The 4Gb limit also applies to GFX card RAM. So if you have a 512 Mb GFX card and 4Gb of RAM installed XP will only be able to address 3.5Gb of the RAM. There is no way round this in a 32-bit system.
 
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