Upgrade Question (fsb ram ratios etc)

[tommyboyo]

Ok, say for example I'm currently running 2gb (2x1gb Dual channel), ddr2-557 ram. Lets also say I have a core 2 duo 6600 @ stock speed (FSB 1066). In this situation I would have an fsb/ram ratio of 1:1, ideal right? So what happens if I want to go up to 4gb RAM, I'd whack in a couple of extra sticks but will this not screw up my ratio? I'd have enough ram to push through data at 2132 (I think), but a FSB only capable of handling 1066.

What happens under these circumstances and how do you ensure you have the most efficient setup? I might be completely off the mark here in my understanding of how all this works, but I'm considering putting together a system similar to the one I mentioned, and really just want to know what the situation is if I need to increase my RAM to 4gb (e.g. for vista).

 

[evongugg]

To run 4 GB you must have a 64 bit system. Windows will recognize something like 3.5 GHZ, when you have 4 GB. For a 32 bit system I would stick with 2 GB.
The extra memory will not change the speed. If you buy DDR2-533, that's what you will have. The memory may be highly overclockable, if it's not value RAM. It is easier to buy faster memory in your case.
If you buy 2 GB and the memory is double sided, you may not be able to add extra 2 sticks. Pay attention to that when you make your purchase.

 

[tommyboyo]

Right ok, I wasn't aware of that but I wouldn't be upgrading to 4gb until moving to vista anyway. By 'double sided' do you simply mean that it could be prohibitively large, physically preventing the installation of another 2 sticks?

What I originally wanted to confirm is the 1:1 cpu:ram speed ratio that everyone keeps referring to as 'the ideal'...here's now I see it -

- fsb on a core2duo 6600 is fixed at 1066mhz (we'll assume no overclocking for the sake of this arguement)

- 2 sticks of ddr2-533 ram in dual channel mode also = 1066mhz (266mhz x2 for ddr2, x2 again for 2 sticks)

- therefore RAM can send data at 1066mhz, and the FSB can process 1066mhz as it's maximum, so everything is equal in a 1:1 ratio and you're getting the most out of both.

However the situation when you add 2 MORE sticks of RAM to total 4gb is that you effectively have 4 sticks each capable of sending at 533mhz, which totals 2132mhz, however the FSB can still only handle 1066mhz. What happens under these circumstances? Does the RAM simply slow down? and what would I do to make sure I had everything set up in the most efficient way? choose another ratio? 4:5? higher? My knowledge is really lacking when it gets down to this level, any help is appreciated!

 

[PCAnalyst]

Here is a great thread that went over the CPU/ RAM issues for clarification.

Here

 

[evongugg]

With double sided RAM you still would be able physically to install extra 2 chips, but the computer would not be able to recognize them.
With 4 sticks you still stay at 1066 MHZ and 1:1 ratio. The number of stick does not change the memory speed.
Hope this helps.

 

[tommyboyo]

Right ok...so let me get this straight - even though you have 4 sticks of ddr2-533, it spreads the load over all of it so that only 1066mhz ever gets sent to the fsb at any one time? and to confirm, ideally if you have 4 sticks of 533, you'd want a fsb of 2132mhz (I know this isn't possible, but just for the sake of argument) to get the most possible speed out of the RAM? If this is true does it not suggest that when you have that much RAM then there will be some kind of bottleneck when it hits the FSB?

 

[Mondoman]

Right ok...so let me get this straight - even though you have 4 sticks of ddr2-533, it spreads the load over all of it so that only 1066mhz ever gets sent to the fsb at any one time? and to confirm, ideally if you have 4 sticks of 533, you'd want a fsb of 2132mhz (I know this isn't possible, but just for the sake of argument) to get the most possible speed out of the RAM? If this is true does it not suggest that when you have that much RAM then there will be some kind of bottleneck when it hits the FSB?

The point you're missing is that what is limiting throughput is the memory controller(s) in the chipset/CPU, not the number of memory DIMMs.

A board with only 1 memory controller can only run in single-channel mode. Its maximum throughput = DIMM throughput x (number of controllers = 1) = DIMM throughput.
A board with 2 memory controllers can run in dual channel mode if the memory is properly arranged. Its maximum throughput = DIMM throughput x (number of controllers = 2) = 2x DIMM throughput.
There are currently no chipsets/mainstream CPUs with more than 2 memory controllers, so it doesn't matter if you add any more DIMMs, the system throughput won't increase any more.

 

[tommyboyo]

Ok, so why is it that you can achieve say 1066 throughput on one channel if you have a stick of ddr-1066, but not if you have 2 sticks of ddr2-553?

e.g. with 2 sticks of ddr2-1066 you could achieve a throughput of 2132 across both channels combined, but you can't achieve that with 4 sticks of ddr2-533?

 

[Mondoman]

Think of the memory controllers as cash registers at the McDonald's counter. Think of the DIMMs as McDonald's employees.

If you only have 1 cash register (single memory controller, thus only single channel mode), throughput is limited to speed of 1 employee, no matter how many employees are behind the counter. This is what happens in older/cheaper MBs with only 1 memory controller.

If you have 2 cash registers (dual memory controllers), then throughput is doubled IF you have 2 employees. This is what happens when running in dual-channel mode. However, if you only have 1 employee, your throughput is still limited to speed of 1 employee, even though you have 2 cash registers.

Your question asks what happens when you have 2 cash registers (memory controllers on MB), but 4 employees (DIMMs). I think you can figure out the answer now...

 

[Mondoman]

Ok, so why is it that you can achieve say 1066 throughput on one channel if you have a stick of ddr-1066, but not if you have 2 sticks of ddr2-553?

One channel = 1 cash register, thus limited to speed of 1 employee (whether employee speed is DDR2-1066 or DDR2-533).

e.g. with 2 sticks of ddr2-1066 you could achieve a throughput of 2132 across both channels combined, but you can't achieve that with 4 sticks of ddr2-533?

2 channels = 2 cash registers. DDR2-1066 employee on each register = 2x DDR2-1066 total throughput.
DDR2-533 employee on each register = 2x DDR2-533 total throughput, no matter if there are extra employees hanging out behind the counter or not.