MacPro5,1 RAM upgrade from 24GB to 32GB, noticeable?

inaka

macrumors 6502
Original poster
Apr 26, 2010
361
2
I have a MacPro5,1 [6-Core Intel Xeon, 3.33 GHz, ATI Radeon HD 5870] that is a workhorse business machine for me. I primarily use it for Illustrator (work) and for Photoshop/Lightroom (photography).

I had Mountain Lion running on it forever, and just upgraded to Yosemite. In running the system profiler, I realized that my machine has 4 RAM slots, but only 3 have RAM in them, 8GB each. (I honestly thought I maxed out the ram a while back, and never paid much attention.)

I just wanted to know if adding another 8GB of ram to the empty slot will even make any noticeable difference at all. It's about $55 for another 8GB of ram for that slot.

Just wondering if anyone has gone through this, or if it's a waste of $$$ as it might be unnoticeable.
Any feedback is appreciated, thanks.
 

ActionableMango

macrumors G3
Sep 21, 2010
9,263
6,249
Nobody can answer this except you:
  • If you are running out of RAM, then adding more RAM will make a very noticeable difference.
  • Conversely, if you are not running out of RAM, then adding more RAM won't result in a noticeable improvement at all.
So what you need to do is run Activity Monitor and click on System RAM to find out how much you are using and whether you've exceeded its capacity or not. Then will know whether or not you will benefit from additional RAM.
 

inaka

macrumors 6502
Original poster
Apr 26, 2010
361
2
Gotcha, thanks. I kind of figured as much and how it would depend on the apps and the number of apps you have running concurrently.

I don't believe I've ever been remotely close to maxing out my ram usage.
 

JeanLCP

macrumors newbie
Sep 16, 2015
13
2
I have the same cMp (5,1 six Core 3,33). I maxed the RAM out to 3 x 16 GB; the firm i bought my cMP from (a small dutch firm, specialized in refurbished MacPro's) advised me not to use the 4th memory-Bank, because the processor (W3680) was triple channel and could and would not support the 4th bank.

As far as I know, the W3680 can not, the X-processors can use the fourth bank.
 

kucharsk

macrumors regular
May 31, 2016
118
74
I have the same cMp (5,1 six Core 3,33). I maxed the RAM out to 3 x 16 GB; the firm i bought my cMP from (a small dutch firm, specialized in refurbished MacPro's) advised me not to use the 4th memory-Bank, because the processor (W3680) was triple channel and could and would not support the 4th bank.

As far as I know, the W3680 can not, the X-processors can use the fourth bank.
The fourth bank is supported, but as it shares a memory channel with the third bank, populating it can actually slow down your system as the memory accesses to both banks contend for the same channel.
 

inaka

macrumors 6502
Original poster
Apr 26, 2010
361
2
Got it! Thanks for the info. I knew there was a reason I left that slot blank in the first place. It's been so long I forgot why. Thanks again.
 

kucharsk

macrumors regular
May 31, 2016
118
74
Got it! Thanks for the info. I knew there was a reason I left that slot blank in the first place. It's been so long I forgot why. Thanks again.
Do note that the difference is largely theoretical and seen only on benchmarks; certainly if your system needs the extra RAM, having it available will likely negate any slowdown because of the shared memory channel architecture as having to deal with memory channel "traffic" is still faster than paging out memory or swapping to even an SSD.

Basically if you've three slots filled and Activity Monitor shows Page Outs or Swap activity, you'll be really happy if you fill the fourth bank; it's just that if you don't need it you'll see slightly better performance if you don't, and most of us fall into that latter category.
 

h9826790

macrumors G5
Apr 3, 2014
12,766
5,577
Hong Kong
Just leave activity monitor open, and then do your work as usual.

At the middle of the, go to activity monitor can check if the memory pressure still green in colour.

If yes, adding more RAM should not give you any significant improvement.
 

Easttime

macrumors 6502a
Jun 17, 2015
562
382
go to activity monitor can check if the memory pressure still green in colour. If yes, adding more RAM should not give you any significant improvement.
Is this always true? I have been using an old MacBook recently. At 4 GB RAM it ran slowly but in the green. I presumed that it was managing the functions I was demanding by throttling. So I upped the RAM to 16 GB and it seemed to run much quicker. Then after a week of that I swapped the hard drive for an SSD and noticed another gain in responsiveness. I did not do any statistics tests, just my impressions.
 

h9826790

macrumors G5
Apr 3, 2014
12,766
5,577
Hong Kong
Is this always true? I have been using an old MacBook recently. At 4 GB RAM it ran slowly but in the green. I presumed that it was managing the functions I was demanding by throttling. So I upped the RAM to 16 GB and it seemed to run much quicker. Then after a week of that I swapped the hard drive for an SSD and noticed another gain in responsiveness. I did not do any statistics tests, just my impressions.
If you swap back the 4G RAM, may be the system can still run fast. I guess it's the HDD causing the bottleneck, not the RAM. However, by increasing the RAM size, the system can use some extra RAM as cache. Therefore, it alleviate the HDD bottleneck a bit (especailly when the system already up for some time, which allow something stored in the cache).

Anyway, you are talking about 4G of RAM, the system will adjust the RAM usage according to the RAM size, only 4G available means the system will only use the RAM when really required, therefore, no extra RAM to accelerate the system. However, OP has 24G of RAM, which is way beyond the OS minimum requirement, in my own observation. The system will usually use about 6-8G of RAM after cold boot, and use the remaining as app memory / cache. In his case, extra RAM can hardly give him any noticeable improvement if the memory pressure is always in green.
 

Philocetes

macrumors regular
Sep 23, 2016
106
34
The fourth bank is supported, but as it shares a memory channel with the third bank, populating it can actually slow down your system as the memory accesses to both banks contend for the same channel.
I read something in a benchmarking discussion whereby the tri-channel was at most 5% faster than 4 slots full, and if the additional memory keeps something from paging to disk its well worth it to take the slowdown on the tri-channel.

Having a 3680 with 32 gig--[populating 4 slots, I would read with interest any reference material that discusses these matters...

thanks.