[someone]

very silly question -- but is there any way to get a Mac Pro from Apple without at least a gig of ram? That way I can buy the rest from Crucial and save a few $$$

What happened to the days when 512 was a lot?

[Landos Mustache]

Nope.

[SirCastor]

Part of it has to do with the fact that you need to install in pairs... The frustrating thing to me with the build to order is that I couldn't make 2gig out of 2x 1Gig Dimms,

[someone]

In pairs? ew...

What's this about increased memory latency with 4 or more slots being used? What's the ideal mid-level (not maxed-out) ram config?

[Landos Mustache]

Apple said to get the best speed you need 4 matching chips.

[MaxPower2k3]

If you buy, say, 4 1GB chips, would it actually be better to take out the original 2x 512 completely so you just have the 4 slots filled? Or does the difference of 5GB vs. 4GB of RAM outweigh the bandwidth hit of having 6 DIMMs?

[mduell]

Crucial does not sell any memory for the Mac Pros yet. They tested it and are having reliability/stability issues. Their heatsinks are smaller, so I'm guessing there just isn't enough airflow in the Mac Pro case to keep it cool. Crucials modules have already been validated by Intel, so it's just a matter of waiting for them to put larger heatsinks on the memory.

Originally Posted by SirCastor

Part of it has to do with the fact that you need to install in pairs... The frustrating thing to me with the build to order is that I couldn't make 2gig out of 2x 1Gig Dimms,

Annoying, but with good reason; four modules provides double the memory bandwidth of two modules.

Originally Posted by someone

In pairs? ew...

What's this about increased memory latency with 4 or more slots being used? What's the ideal mid-level (not maxed-out) ram config?

Four slots filled, with whatever size module you can afford.

Originally Posted by MaxPower2k3

If you buy, say, 4 1GB chips, would it actually be better to take out the original 2x 512 completely so you just have the 4 slots filled? Or does the difference of 5GB vs. 4GB of RAM outweigh the bandwidth hit of having 6 DIMMs?

Depends if your app/task is memory latency sensitive or memory capacity sensitive.
It's a bandwidth hit when you go under 4 modules; it's a latency hit when you go over 4 modules.

[rotuts]

Md

would you describe the latency hit a little more:

my Pro will arrive next week with the 2 x 512 as im awaiting Crucials RAM after they redo the heat sinks

then Ill get 2 x 1gb to have four slots filled.

if i decided later to get 2 more 1 gb, then Ill have 4 x 1gb and 2 x 512, there for id suffer a latency hit?

let me know how this might effect the above so i can lear more about the latency issues

cheers

hope Crucial hurries up!!

rotuts

[brokenjago]

Yes, you'd get a 3-5ns latency hit. Note that ns stands for nanoseconds.

[mduell]

Originally Posted by brokenjago

Yes, you'd get a 3-5ns latency hit. Note that ns stands for nanoseconds.

A minimum of a 3-5ns latency hit, which at 2.66Ghz is 8-13 clock cycles.

[reader50]

From my reading of Anandtech's discussion of FB-DIMMs, you only get the latency hit when you access RAM that is in the last four slots. So if you got 4 x 1GB, I'd move those to the first four slots and move the 2 x 512MB to the next couple slots. You'd only pay the price when hitting up the very top of your RAM space. That doesn't sound so bad.

To clarify, adding RAM beyond 4 DIMMs won't slow down the first 4. The later 4 will have higher latency. So always put the largest DIMMs first.

[rotuts]

Great Tips!

will rememeber and thanks again

hoping its clear which are the "first" I bet thats the one where the default rams lives in!

don't use smilies much, but why not?
rotuts

[reader50]

The RAM slots are numbered upwards from the motherboard. The first ones are the ones closest to the motherboard. You know, the ones that are the hardest to reach. That should be easy to remember.