Need Advice on Building a New PC

[Agent]

I didn’t provide any in-depth explanations as people who had pointed things out got a fairly abrupt response, but that post comes across as much more friendly Its easy to forget that there is a person at the other end of every post sometimes, but a little politeness goes a LONG way online

But anyway, to clear a few misconceptions up.
The reason Dual DDR isn’t like RAID is fairly simple.

On a RAID system (assume we are talking about RAID 0, 2 drive set-up here), the OS will use both drives as one logical drive. The easiest way to think about it (although this is not be 100% accurate – I am just trying to simplify a point to illustrate the differences) is that when a file is written it does 50% to one drive and 50% to another. The upshot of this of course is that when it is read back, 2 drives are reading 50% from each, which theoretically[1] doubles the speed.
These drives are operating exactly the same as they would in a single drive configuration[2] , apart from the RAID controller deciding which bits to write to which drive.

Dual channel is a different beast.
Instead of splitting up information and spreading it across two sticks, it offers 2 independent routes to the RAM from the CPU.
The upshot of this method is that the memory is segregated from each other into different channels and controlled independently by a memory controller for each of these. Reading information from one stick does not increase its speed anymore than it would without Dual DDR. It performance only shows when the bus to the RAM is almost saturated. In actual real world use, this rarely happens. This is why you see a minimal performance gain in actual applications but a bigger gain in synthetic benchmarks; They are designed to stress that aspect of the system.
With two controllers offering 64bit addressing to each of these channels, it raises the total amount of addressable RAM space to 128bit.

The easiest way to think about it compared to RAID 0 is with RAID 0 the drives are the limiting factor not the bus; So by combining these, it helps raise the overall speed of transfer to the rest of the system.
With Dual Channel DDR, it’s not the RAM itself that’s the potential bottleneck[3], but the bus that connects to it, the opposite of what RAID 0 tries to achieve.

Hope that helps

[1] Actually getting 100% of the speed is a different topic in its own right.
[2] Excluding some enterprise class and specifically optimised RAID drives
[3] This rarely happens.

[Andaho]

Thanks If only it ended there though - because that doesn't really explain why 800MHz is only marginally faster than 533MHz DDR2? But that's the not question I really want answering... What would performance be like with 3 sticks of 1Gb? (due to 4Gb being too much for a 32bit OS) - I've never heard of anyone building a system with 3Gb before - surely there must be a good reason for it?

[Agent]

because that doesn't really explain why 800MHz is only marginally faster than 533MHz DDR2?

Its simply because the bandwidth of the 533MHz bus is hard to saturate, never mind an 800MHz based one.
Its like having a car with a top speed of 70mph and using it on a road with a speed limit of 100mph. Just because the roads limit is at 100mph, it doesn't mean the car can do it.

But that's the not question I really want answering... What would performance be like with 3 sticks of 1Gb? (due to 4Gb being too much for a 32bit OS) - I've never heard of anyone building a system with 3Gb before - surely there must be a good reason for it?

A 32bit OS can address up to 4GB, but the 32bit environment on most systems means that some of that addressing space is taken by other devices on the system such as the graphics card ect.
This can be overcome by using PAE, but is generally a lot of hassle and not supported by a great number of motherboards. Then there is the issue that 32bit OS's are generally not optimised to be used with such a high RAM size too.

You can use 3GB fine, and a few people actually do use it (I ran it for a while). Most people don't bother with this set-up though as the majority of people do not use 2GB currently.
There is no technical reason why you can not run 3GB though, so the most likely reason you don't see it is due to the way RAM is pre-packaged in kits of two sticks.

As for performance - that depends on the RAM itself (timings ect.) and possiably the memory controller. A lot of controllers get arsey about >2GB RAM and will only do so at low timings. This is usually down to it having to deal with more sticks though and the higher workload that is associated with it.

[Andaho]

I was actually thinking on the performance complications on having 2 sticks in dual channel mode, and then the 3rd?

[Agent]

I was actually thinking on the performance complications on having 2 sticks in dual channel mode, and then the 3rd?

Well as Dual DDR has a minimal gain anyway, running another stick can't effect it any more than the difference between a non dual DDR config, and a dual DDR config, so adding a 3rd stick will have a minimal impact on performance in that respect.

Dual DDR doesn't strictly need "matched" pairs, its just recommended.
Some motherboards will work in dual DDR mode with unmatched sticks, some wont. Its purely down to the boards BIOS and the memory controllers.
A *lot* of motherboards tend to default to a non dual DDR mode when using unmatched sticks though these days, purely down to not wanting to present the user with an unstable system or requiring them to go and manually edit memory timings in the BIOS.

[Sprite]

Yeah, I'm looking for someone to comment on that too, I've spent most of today just looking at different cases!

I bought a TA250 and it's very basic, came with a PSU that was a POS (blew up in less than a day), steel is very thin and doesn't leave much to be desired for, spend the extra bit of dosh and get a decent case tbh