[Abbas]

I am thinking of replacing my Windows Home PC with a Mac Pro. This PC is currently used by three people with three user accounts and I have it outfitted with 3GB RAM and that makes it quite fast even with all three users logged on.

Now that I'm debating on upgrading to Mac Pro, I wont have much money left to upgrade RAM at the moment, however, I will buy a 2GB kit in a few months. My question is- how is OS X with multiple Users and Memory Management. Will it slow down the machine if all three users are logged on? (Obviosuly, only one will be active at a time).

Also, how are applications stored in RAM? For example, If I already have iTunes or Mail running, will another user require a whole new instance of these applications? For example, lets say that if Mail takes 50MB to run, am I losing 100MB or RAM when two users are running it?

Thanks
-a

[jasong]

I know that my PowerBook G4 1 ghz felt like it slowed down a bit when running with 2 users prior to upping the memory to 1 gig, but you are talking about a much slower rig to begin with. It's never been something that has made me crazy though. Why don't you go to an Apple store (or anywhere they sell Macs) and try it out?

Of course the answer for you will vary based on what apps you are running. If all three accounts are running Mail, iTunes, and Safari, then I doubt the system will have any problems keeping up with that. If all three are running Final Cut Pro and Photoshop and Quark simultaneously, yeah, it'll probably slow down (I could be wrong though, anyone here ever tried that?).

Each user will run it's own instance of the application, so yes, if you are running Mail, and each of the other two users are running Mail, your Mac has three copies of Mail loaded at the same time. What will happen is the copies of Mail for the two background users, which aren't doing much of anything (maybe just occasionally downloading new mail), will get paged out to disk. So yes, there is a RAM penalty for running multiple users, but since you are starting with 1 gig to begin with and upping it to three eventually, I doubt you will be hurt much by it. Unless of course you are talking about running mega RAM hungry apps all the time.

[P]

The RAM situation will not be as bad as it might look at first. What will happen is that everything that isn't used will be paged out into virtual memory, leaving memory free for regular use. The VM system in OS X is very good for desktop apps (FreeBSD, and to a lesser extent Linux, have an edge in server apps, but for desktop apps OS X is very good) and the only time you will notice it is when swicthing apps.

Running two instances of iTunes will not require twice the regular amount of real RAM, because OS X uses "copy-on-write" - meaning that two virtual memory pages can be referenced by the same real memory page as long as the content of them is the same, which it will be for e.g. the program code of two instances of the same app.

1 gig RAM may be slightly on the low side, at least if you plan to use Rosetta translation for PPC apps, but 3 gigs is more than enough. If the non-active users make a habit of closing the mor memory-intensive apps when switching to another user, you will never have a problem.

[bowwowman]

OS X is built from the ground up (based on Unix) as a multi-user OS, unlike your current hack-a-sack confabulated OS. The memory management in OS X is light years more advanced than OS 9 & earlier mac systems, let alone that other OS, and that extends to complex task of managing system resources allocations in a multi-user environment.

So bottom line: once you increase the ram to 2GB or more, under normal circumstances, there will be NO problems, unless they all decide to run PS, FCP, Motion and other ram hog apps simultaneously, which could still be resolved by upping the ram even more, say to 4, 5 or 6GB

[Big Mac]

With the same amount of RAM, OS X can handle more logins and open applications than Windows can. At a certain point any system will slow down if there VM is used too heavily, but OS X can do a lot with a little. For example, I ran my G5 for a short time with only 512MBs of RAM, and I had four users logged in with moderate application load in each without much slowdown. Having fast hard drives likely makes an important difference, of course. Btw, OS X is also far superior as far as multitasking is concerned.

[Abbas]

Thanks for all the comments. I have already gotten the new 150GB Raptor which should help a bit until more memory is added.

I will be using Rosetta until Microsoft Office and Photoshop become universal so I'm sure there will be slowdown but is Rosetta more of a CPU hog or a memory hog?

-a

[Catfish_Man]

Both, unfortunately. Rosetta does translated code caching to get mostly-acceptable performance, but that eats ram.