Quick memory question

[gravyboat]

Hello,


I'm confused about memory and would appreciate any clarification.

I always hear that more memory is better, but what if the following is true?

1. Running an iMac G5 with 512 mb

2. No heavy apps. According to Activity Monitor, I always have between 80-100 mb of free memory.

If I'm not exceeding my current ram, would there be any benefit to adding say another 512? Or would the additional ram be completely wasted (unless more memory intensive apps were used)?

In other words, would the ram allocation (or whatever the correct term is) be different (more efficient, faster) if I had 1gb as opposed to 512mb if I never went over about 400 mb in usage?

Thanks so much for any comments.

 

[mklos]

You may or may not see any immediate benefits of increasing the RAM, but Mac OS X has an excellent memory management system. If more RAM is available to use to doing things, it will take advantage of it.

But its not just OS X that uses RAM. Its any other apps you have open and they will also use whatever RAM they need to if available. If its not available then the OS and/or app can start to run a little sluggish.

People always say the more RAM the better with OS X, and thats certainly true, but only to a point. For example you're not going see any huge benefits of putting 8GB of RAM into a PowerMac G5 over it having 4GB for daily finder, safari, mail, etc tasks. Where it does become beneficial, is where you start doing things like importing and exporting clips/movies in iMovie, or FCE/FCP. Things that tax the CPU are also generally things that use a lot of RAM.

Just think of this, if the RAM is there, the OS and/or app(s) will use it if needed. So you can add more RAM and still have less than 400MB left when using your computer. Thats just because the OS and apps have more RAM to use. It will make your computer more efficient. Its kind of like having more money. The more money you have, the more you can spend, but only if you need to.

 

[gravyboat]

mklos,


Thanks for the detailed reply. This is all very interesting and I appreciate you sharing your knowledge. One last question and I promise that'll be it!

To continue the money metaphor:

Let's say I have two sacks of money, Sack1 and Sack2, each with 512 units. To run my computer I need to spend 400 units (with Firefox, iTunes, Thunderbird and Appleworks open I use about 400 mb).

Let's say I never exceed 400 units. Does all 400 units come from Sack1? Making Sack2 superfluous? Or does the OS draw say 200 from Sack1 and 200 from Sack2?

In other words, as far as ram-related performance goes, if I never use more than 400 mb would I get the same performance from one 512 chip as I would from two 512s?

Sorry if I'm being tedious here. Just curious. Thanks!

 

[MikeTheC]

The "200 units from Sack A, 200 units from Sack B" is referred to as Memory Interleaving. I don't know for certain, but I'm fairly confident that most modern Macs (and likely most if not all G5-based ones) use Memory Interleaving.

It's philosophically the same as RAID Striping, and I believe yields similar benefits.

Now, let me give you my own experience. I bought a new PowerBook G4/1.5GHz, which came with 512MB RAM. Most of what I have used it for since the date of purchase is web surfing (primarily with Firefox), email (primarily with Entourage), local and streaming music via iTunes, writing with a combination of TextEdit and MS Word, and infrequently I'll futz around with Garage Band. (I also have done other relatively demanding things, like work in Photoshop and InDesign, but I'm excluding them from this discussion.)

About a year after I bought the unit, I upgraded it to 768MB by taking one of the two 256MB RAM modules out and replacing it with a 512MB unit. Several months ago I replaced the other 256MB module with a 512MB one, bringing my total now to 1GB. Here's what I found:

Going up from 512MB gave me a more noticeable performance improvement than specifically going to 1GB. Now, that isn't to say there wasn't any performance improvement going up to 1GB, but I didn't really notice it as much.

Obviously, as the saying goes, "Your mileage may vary.", but I think it's a reasonable proposition to propose you upgrade your system. I would suggest that your strategy should change from one of "Justify not upgrading" to "shop around for the best price on good -> premium RAM, and upgrade as far as you can reasonably conscience and/or budget".

 

[gravyboat]

Hey MikeTheC,

"Memory interleaving"-- sounds almost poetic! Thanks for helping me learn something new today.

I appreciate your perspective. A friend will have a spare 512 after he upgrades his system and after hearing these replies I think I'll go for it.

Cheers!

 

[CanadaRAM]

Of course, memory interleaving (dual channel) happens only with PowerMac G5 machines and Intel Macs. Not available on iMacs, Powerbooks, iBooks or G3 and G4 Macs

 

[Irish Dave]

In my experience I consider 1 Gb of ram to be the minimum required for MacBooks and 2 Gb for iMac's and Powermacs. Apple is very good at memory management and will wisely use as much as you care to install.

More is best !!!

Dave

 

[gravyboat]

Hey there CanadaRam and Irish Dave,


Thanks for the additional info and suggestions. I'm going to get the extra 512 and see how it works out. Won't cost much, and I'm curious about the results.