[Todd Madson]

Hello...

I recently upgraded my G5 from 3.5 gigs of ram to 6. Since memory is so cheap
I'll probably be upgrading it to 8 gigs before long. May as well max it out now
that ram is $29 a chip for this machine (G5 2.5 dual).

I work on a lot of music related projects, some of which with lots and lots of 24-bit
samples so the more memory the better. It also seems to help when dealing with
giant digital video files.

I've also noticed that the machine just seems to run faster with more memory.

So, those of you with lots of memory (say larger than 4 gigs) what do you use the
machine for and what have you found it helps with?

Have you done something unusual such as creating a large ramdisk and running
disk intensive applications out of the ramdisk or other fun and time saving things?

[Drakino]

Even if you don't use a single memory heavy application, having more RAM just makes program launching faster, or makes it easier to keep open all your commonly used apps. I don't restart my Mac Pro or Macbook Pro, choosing to just let them sleep when not in use. I can always come to the Mac Pro, click on Mail, and have it up and ready to go in under a second. Same for iPhoto and iTunes when I plug in the iPhone.

As for actual memory eating uses, VMWare tends to be open a lot on my Pro, and it is nice to be able to throw 2GB at a virtual OS and not have OS X feel like it is slowing down. I have 6GB total right now, and still have 4 open slots for future expansion before I have to start replacing sticks of RAM.

[goMac]

I used to have 2 gigs on my Mac Pro. I found it was too lightweight for some stuff I did (way too small for using VMWare). I upgraded to 4 gigs and am looking to add more...

[tooki]

The 2008 Mac Pros have an interesting quirk in their memory controllers: they only achieve maximum RAM throughput once all eight RAM sockets have been populated. (The throughput ranges from 6.3GB/sec with two modules all the way to 7.5GB/sec with eight modules, according to BareFeats testing.)

That's why I bought my Mac Pro (same model as yours) with 2GB from Apple and then got 6x1GB modules from OWC to bring it to 8GB, when all I need RAM-wise is 3-4GB.

antonio

[EricTheRed]

Originally Posted by Todd Madson 

Hello...

I recently upgraded my G5 from 3.5 gigs of ram to 6. Since memory is so cheap
I'll probably be upgrading it to 8 gigs before long. May as well max it out now
that ram is $29 a chip for this machine (G5 2.5 dual).

I work on a lot of music related projects, some of which with lots and lots of 24-bit
samples so the more memory the better. It also seems to help when dealing with
giant digital video files.

I've also noticed that the machine just seems to run faster with more memory.

So, those of you with lots of memory (say larger than 4 gigs) what do you use the
machine for and what have you found it helps with?

Have you done something unusual such as creating a large ramdisk and running
disk intensive applications out of the ramdisk or other fun and time saving things?

Mac Pro, 6 GB RAM using all eight slots. Nothing unusual. I use it for trading securities and derivatves.

[tooki]

Love the setup, but your subwoofer belongs on the floor for optimum performance!

antonio

[seanc]

Originally Posted by tooki 

Love the setup, but your subwoofer belongs on the floor for optimum performance!

antonio

Seconded. I'll never work out why people put them on their desk. At the end of the day, it just takes up more desk space.

Nice screens by the way. Are they all the same type? What's your graphics card configuration?

[mduell]

Originally Posted by tooki 

The 2008 Mac Pros have an interesting quirk in their memory controllers: they only achieve maximum RAM throughput once all eight RAM sockets have been populated. (The throughput ranges from 6.3GB/sec with two modules all the way to 7.5GB/sec with eight modules, according to BareFeats testing.)

The actual performance difference between 6.8 - 7.0 GBps (4 modules) and 7.5 GBps (8 modules) is likely to be quite small unless your app is very sensitive to memory bandwidth. I think you're better of initially going with 4x2 or 4x4GB to leave room for future expansion.

[tooki]

It's been tested at 6.4*-7.5GB/sec, scaling linearly between 2, 4, 6 and 8 modules (excluding the unsupported configuration of two modules on one riser, which massively slows throughput. OWC has a page about this.

As for future expansion, for me at least: since my current RAM needs lie somewhere around 2-3GB, it's very unlikely that I will ever need to go beyond the 8x1GB I have now. And if I do, I'm not gonna sweat pulling out a pair of DIMMs to make room.

As for memory bandwidth sensitivity: what app isn't sensitive to some degree? Memory bandwidth is critical to overall CPU performance. Going from 6.4GB/sec to 7.5 is a 17% difference. That's huge. Many processors in the past have proven to be limited not by their internal processing power, but by the memory not being able to keep the CPU fed with data. With modern processors, whose internal clock speeds well exceed the system bus speeds, CPU starvation can and does happen.

*I said 6.3 before, my mistake.

[chipchen]

for Mac Pro's... 8GB really seems to be a sweet spot it seems...

[mduell]

Originally Posted by tooki 

excluding the unsupported configuration of two modules on one riser, which massively slows throughput.

Did you just call the default configuration that most Mac Pros ship with unsupported?

Originally Posted by tooki 

As for memory bandwidth sensitivity: what app isn't sensitive to some degree? Memory bandwidth is critical to overall CPU performance. Going from 6.4GB/sec to 7.5 is a 17% difference. That's huge. Many processors in the past have proven to be limited not by their internal processing power, but by the memory not being able to keep the CPU fed with data. With modern processors, whose internal clock speeds well exceed the system bus speeds, CPU starvation can and does happen.

Most of them. See this test at Anandtech where 6 of 14 benchmarks show no gain, another 5 show gains less than 5%, and just 2 show double digit (but under 20%) gains.

If apps were just doing streaming reads they'd read the entire memory in a matter of seconds and few would care. But they're not, they're doing random reads and the 100ns latency of FB-DIMMs kills performance. See this benchmark from Anandtech, where the Mac Pro achieves just 20% of its 21GBps potential for reads (4.3GBps), while a cheap Core 2 Duo desktop system (with regular old DDR2) hits 6.8GBps.

[SierraDragon]

Originally Posted by mduell 

...I think you're better of initially going with 4x2 or 4x4GB to leave room for future expansion.

Fully agreed.

-Allen Wicks

[bearcatrp]

I have 8 gb ram (8X1gb) in my pro. I do video editing and seems to run fine. I think 2gb per core is sufficient. When I upgrade my quad to octo, then time to increase to 16gb.

[tooki]

Originally Posted by mduell 

Did you just call the default configuration that most Mac Pros ship with unsupported?

The supported configuration on the 2008 Mac Pro for two modules is one on each riser. I know, I sold many of them and bought one such machine myself.

[tooki]

Originally Posted by mduell 

Most of them. See this test at Anandtech where 6 of 14 benchmarks show no gain, another 5 show gains less than 5%, and just 2 show double digit (but under 20%) gains.

If apps were just doing streaming reads they'd read the entire memory in a matter of seconds and few would care. But they're not, they're doing random reads and the 100ns latency of FB-DIMMs kills performance. See this benchmark from Anandtech, where the Mac Pro achieves just 20% of its 21GBps potential for reads (4.3GBps), while a cheap Core 2 Duo desktop system (with regular old DDR2) hits 6.8GBps.

Those tests are on the pre-2008 Mac Pro, whose memory controller did NOT have varying throughput depending on the number of modules installed. It's a new phenomenon found only in the 2008 Mac Pro, which incidentally about doubles the memory throughput over its predecessors.

Please look at the Barefeats and OWC benchmarks I linked to earlier to compare how the pre-2008 (667MHz FB-DIMM) and 2008 (800MHz FB-DIMM) models differ in RAM behavior.