Memory question?

SixTwoSix

SixTwoSix

SixTwoSix

Soldato
Joined
14 Sep 2007
Posts
15,697
Location
Limbo
Whats likely to run faster/better..

2x2Gb sticks 800Mhz ddr2 ram or 4x1Gb sticks 1066mhz ram, I know the obvious answer is the 1066MHz ram, but as I asked in an earlier thread, it seems as though mobos prefer 2 sticks to 4 sticks, so I wondered if i'd lose the extra performance on the 1066mhz by having 4 sticks?

I also know it depends on the make/model as well, just after a general answer, thanks!
 
Basically, unless you are doing some really insane overclocking then you don't need nor will you see any real benefit going for 1066MHz RAM over 800MHz RAM.

At default sppeds a Core 2 Duo/Quad will be running on a FSB of 266 or 333.
So even DDR2 667MHz RAM is fine.
This is because as a rule you will set the memory ratio up as 1:1.
This is how Intel systems like to run, it gives the processor enough memory bandwidth so nothing gets throttled.
Now you can run the memory at different ratios and give yourself more memory bandwidth - but you aren't going to see any advantage - it is the speed of the memory rather than the amount of bandwidth that will make any kind of difference.

Imagine if you like everything running at stock speed.
The DDR2-667MHz RAM is like having 2 lanes of road all to yourself (The CPU).
The CPU can run as fast as it likes as it has got two lanes of road.
Now you could increase the bandwidth (slam in some 1066MHz RAM) and now what you've got is 4 lanes of road to drive down.
However you were already going flat out on 2 lanes of road - the extra 2 lanes don't give you any benefit.

If I was buying DDR2 right now I'd stick with 800MHz, buy some with some quite good timings and go for about 4GB of the stuff and not expect to pay much more than around £80 or so.
 
bit of a n00b question. i have a cpu with 1066fsb. if i wanted to max it out (without overclockig) what would be the lowest spec memmory? is there a guide on how fsb and memmory speed are calculated and how they link up?

And does this mean in my new build im putting together with a 1333 fsb, ddr800 would be just as fast as ddr1066? could save me a small fortune :P
 
Last edited:
toothe said:
bit of a n00b question. i have a cpu with 1066fsb. if i wanted to max it out (without overclockig) what would be the lowest spec memmory? is there a guide on how fsb and memmory speed are calculated and how they link up?

And does this mean in my new build im putting together with a 1333 fsb, ddr800 would be just as fast as ddr1066? could save me a small fortune :P
Click to expand...

With an intel cpu the fsb clock speed is 1/4 of the transfer rate because it does 4 transfers per clock cycle. Eg an fsb of 1066MT/s is 266.5MHz which then you then multiply by the cpu's multiplier to get the clockspeed, eg 8x multi = 2,132MHz.

Now because DDR memory sends data at the rise and fall of each clock it's transfer rate is twice it's clockspeed, eg 1066MHz ram is 2,132MT/s. Remember than DDR2 memorys bus speed is twice as fast as the actual memory chips are running at so the actual chips themselves are running at 1/4 of the transfer rate, eg 1066MHz ram has chips running at 533MHz. So 1066MHz memory is good up until the cpu's fsb reaches 533MHz. Which with a cpu multi of 8x is 4,264MHz!

Put simply, you need DDR2 memory that has a MHz rating half of that of the cpu's MT/s rating. Eg your 1066MT/s fsb cpu needs 533MHz ram. Anything higher than that, and the cpu can't take advantage of it.

Also remember that dual channel mode gives double the memory bandwidth, so having two sticks of DDR2 533 ram gives the same amount of bandwidth as one 1066MHz stick.
 
Last edited:
so if i were to buy a quad core with 1333mhz fsb when they come out (not an extreme) would the pc2-6400 max out its fsb?

if so why the high bw memmory?
 
thanks, think ill go with ddr 800. gives me a little future proofing.

whats the main diff between ddr2 and 3. sorry for all the questions enjoying the learning curve though.
 
It runs the bus at 4x the clock speed of the memory cells instead of 2x. This allows more data to be transferred without increasing the clock speed of the memory cells.

You'll still need ram rated at half the fsb of the cpu, eg 1,333MT/s cpu will need DDR3 667MHz ram.
 
Last edited:
o yeah i remeber it reads data at the bottom top and center of each clock.

Does this mean though that ddr3-1333mhz is actually clocked slower than ddr2 of the same speed, or are they clocked the same but run slower? thanks
 
toothe said:
o yeah i remeber it reads data at the bottom top and center of each clock.

Does this mean though that ddr3-1333mhz is actually clocked slower than ddr2 of the same speed, or are they clocked the same but run slower? thanks
Click to expand...

The bus speed is the same, but the memory cells run at half the speed of ddr2, it gives the same bandwidth but higher latency.
 
Well price is because it is a new technology.
If you take the average memory manufacturer.
At the moment something like 90% of their production will be DDR2 modules.
Then somewhere around 5% each on old DDR (to keep those older systems running and also STB's tend to use this) and DDR3 (new technology, not much supporting it - at the moment).

DDR3 is going to offer higher bandwidth but also increase latency.
Right now the extra bandwidth isn't really required, however as the FSB on CPU's increase we will need it.
DDR2 will not scale above 1066Mhz - whereas this is more or less the entry point for DDR3.
The increased bandwidth/increased latency system has historically been good for Intel CPU's.
If we remember back to RDRAM - although there was initially a problem with price and ultimately we saw the back of it, the early P4's all worked a lot faster in an RDRAM system.
Even DDR couldn't offer the bandwidth that the P4's wanted and it wasn't until the very first dual-channel DDR chipset from Intel was released that there was any real alternative to RDRAM if you wanted the best performance possible.

DDR3 isn't needed right now, however as the FSB increases on CPU's it will become needed as DDR2 simply won't scale much faster.
 
You must log in or register to reply here.
Back
Top Bottom