Diagnosing a slow running Mac – Part 1: Memory

This short series will discuss some of the common problems that can slow your Mac down dramatically. In this installment we’ll look at memory, also known as RAM.

Over the years I’ve had probably hundreds of people say to me “my Mac’s running slowly, should I get a new one?”. Typically they’ll have gone to one of the Apple Mac retailers in Bath or Bristol to buy a Mac and had the virtues of the latest Macs extolled to them, and left with the warm glow of certainty that spending lots of money with transform their lives.

Sometimes this is true. Newer, faster hardware may be the solution. But often it’s not the whole story. There are a large number of factors that control the perceived performance of a computer and working out which is the “Rate Limiting Step”, to borrow a phrase from chemistry, can go a way to getting better performance from what you already have.

So how do you know if I have too little memory? The surest sign is that when you have a number of programs open, when you try to switch between them the computer grinds to a halt as the hard drive thrashes noisily. So what’s going on?

For every program that you have open, the Mac has to put aside space to remember what the program is doing. If it can it’ll use free space in the RAM (the ultra-fast short term memory of the computer). If there is not enough free space in RAM, it’ll write it to the hard disk, which is many many times slower. Think in these terms: when you go shopping, often you can remember what you want in your head and recalling is almost instantaneous. But sometimes your shipping list is too big to remember; so you have to write it down, then read it to remember what you wanted. Much, much, much slower. When you have insufficient RAM, you Mac will constantly be writing information to the hard disk, which is slow.

You can use the Activity Monitor application to see how much RAM programs are gobbling and how much the hard disk is being thrashed. Look in the System Memory tab and see how much “Free” memory you have and particularly look to see if the “Page Outs” increases over time. “Page Outs” indicates how frequently the computer is having to use swap space instead of RAM.

If the answer is a lot, try closing the programs that gobble the most RAM. Everything runs quicker? Then you need to buy more RAM…