There is a consistent theme in various Apple Support Communities, here, and in other hardware and software communities
People with Macs which have 4GBs of RAM are asking, "Why is my Mac so slow under Lion, when it worked fine with Snow Leopard?"
I have suggestions for you if you are considering upgrading to Lion, no matter how much RAM you have, but especially if you have 4GBs or less. Lion uses more RAM, and this may hurt your performance after the move to Lion. You need to plan for this
- Check Activity Monitor for Page Outs after you have been using your Mac normally for some hours. If Page Outs are zero or very close to zero, then you'll probably be happy with Lion
- If Page Outs are not zero, identify your most commonly used apps which are significant consumers of RAM, and change them so that they run in 32 bit mode, not 64 bits, then reboot
- Again, check Activity Monitor for Page Outs after you have been using your Mac normally for some hours. If Page Outs are zero or very close to zero, then you'll probably be happy with Lion
- If you are still getting Page Outs, then try running fewer apps concurrently, but only if you can live with this compromise
- If you still haven't reduced Page Outs to almost zero, then either stay with Snow Leopard, or upgrade your RAM
How do I change an app to 32 bit mode?
- Go to your Applications folder, find the app, select it and press Command-i
- A window will open titled "applicationname Info" and about half way down you should see "Open in 32-bit mode" with a checkbox beside it. Check it.
- If it doesn't say that, then look in this window for "Kind". If it says "Application (PowerPC)", then you have another issue to resolve before upgrading to Lion, because this app will not work under Lion.
How much RAM is enough? And how much time should I spend agonizing over how much to get?
- RAM is cheap, so if you don't want to spend a lot of time in decision-making, just add at least 4GBs if it will fit, or 8GBs if you plan to keep the Mac for a while, or bite the bullet and just max it out, unless that would be just too expensive.
- If the budget is tight, or the Mac is an older one with limits on RAM, consider 2 GBs an absolute minimum upgrade
Why should I change the apps to 32 bit mode? Why can't Apple "fix this problem" for me?
64 bit mode was introduced to allow apps to exploit large memories. Your Mac is not a large memory Mac. This is not a problem to be fixed by Apple. Use the app in 32 bit mode on a small memory Mac.
But Apple says that Lion needs only 2GBs to work! What's going on here?
It is true that Lion will work in 2GBs. It is not necessarily true that the experience will be enjoyable, unless you run apps which have low RAM demand and run few of them. For example, if you just wanted to run TextEdit alone on a 2GB Mac, you'd probably get great performance under Lion. It's marketing-speak. If you ask me, I'd say that 8GBs is the smallest realistic RAM size for Lion if you prefer a hassle-free experience, and if you can get more, do it.
Why is Lion using up more RAM, this sounds like it is less efficient than Snow Leopard, isn't it?
New releases of operating systems always use more RAM. Why? To save I/Os, to save you time, and to fit new function into your system. Because RAM is cheap and getting cheaper all the time, OS designers are always looking for ways to use more RAM if it will provide a benefit to the end user. What they are doing is optimizing expensive resources, like your CPU, and HDD accesses. And your time! RAM is not an exensive resource.
Hope this helps!