Sharing the memory

Sharing the memory
Mac Tip #286/25-April-2007

The best money you can spend on a computer is to give it more RAM, the working space for your computer. It’s like a kitchen bench: you can easily make a cheese sandwich in a tiny space, but to make a three course dinner for 10 you’d better have plenty of room.

There is a lot going on with the RAM.

There is a lot going on with the RAM.

Each process running on your Mac takes up a certain amount of RAM. In theory each one takes just as much RAM as it needs, when it needs it and then gives it back. But just as in real life where the last family member to make a sandwich didn’t put the bread away or wash the knife, some processes aren’t so well behaved.

Click on the System Tab near the bottom of the Activity Monitor window to see how the computer’s memory is being used. [Last week’s Tip, How much of the Hard Disk is used?, introduced Activity Monitor.]

The pie chart in the screenshot shows that I have 2 Gigabytes of RAM. The list on the left shows almost 175Mb is being used for ‘Wired’ memory — that’s memory that’s actually in use.

There’s another 999Mb Active — also supposedly in use. If necessary that can be swapped out to virtual memory.

Virtual memory is hard disk space that can be used temporarily as memory. That’s like sitting at the kitchen table to peel the spuds if the bench is too full to do it there.

699Mb is Inactive. Something was using it, but not right this minute. That can be swapped (paged) to virtual memory.

The 1.83Gb figure is the total of the left column. There’s a meagre 171Mb actually free.

Photoshop has grabbed a good chunk of Real Memory.

Photoshop has grabbed a good chunk of Real Memory.

Memory is a shared resource on your Mac. The applications you have running should not all need the whole lot at the same time, just as in a city it’s not expected that every driver will be on the same road at the same moment.

But just as Aucklanders suffering gridlock know they need more roads, Activity Monitor can show you if you’re running more applications at one time than your Mac can comfortably handle. The solution may be more RAM, a newer Mac, to Quit applications you’re not currently using, or even to work a bit less.

Next week: How much of the Hard Disk is used?

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  1. Miraz Jordan said:

    Well, Apple say:

    If the combination of Free and Inactive is very low, then you might need more memory.


    This is a very useful page: ‘Enhancing Performance Of Mac OS X’:


    It explains that Page ins/outs give you a guide to your RAM requirements.

    Macworld contribute: ‘Upgrading RAM: FAQs’:

    If the pie chart is mostly green and blue (representing free and inactive memory, respectively), then you’re in good shape. If the chart is mostly yellow and red (active and wired), then you’re running out of RAM and may experience slowdowns.

    Watch the Page Ins/Outs numbers. If page outs are increasing continually, you need more RAM.


    Hope that helps.

  2. Bill Roberts said:

    Is there any rule of thumb regarding how much memory I should have?

    Somewhere I got the idea that green (free) and blue (inactive) memory should be around 25%. If red (wired) and yellow (in use) memory exceeded 75% that my Mac’s performance would suffer. Another idea is that whatever memory was installed in the factory should be doubled by the user.

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