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mloman
Asked: 2011-12-21 04:56:06 +0800 CST

Is there a difference between SWAP and Cache memory?

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I installed the indicator-multiload 0.2-0ubuntu1 from the software center. (It's very similar to the gnome panel indicator showing memory and CPU graphs)

When I click on the Unity panel which shows the little memory graph, it says ;

Mem :1.451 GB Cache: 2.581. This is also represented in the color graph.

However, when I load the System Monitor, SWAP is at a flat 0.

Is this normal, or could there be a bug in either the System Monitor or Panel Indicator?

indicator

2 Answers

  1. Yes. They are a complete different thing, even the opposite in a lot of ways. I will try to explain both simply and short. Note that this answer are just a simplification and the real thing is quite more complex. Click on the wikipedia links for a better explanation.

    • Disk Cache memory: This are chunks of the physical memory, the RAM, used to store files. That way when a program needs to read the file, it's fetched from memory instead of the hard disk. This is done because memory is way faster.
    • Swap: This is a place on the hard disk (usually a dedicated partition) that is used to store programs or data that can't fit in memory, like when a program grows more than the available memory. SWAP is way slower than RAM, so when you hit swap the computer gets slower, but at least the program can work. In linux swap is also used to hibernate, or to move low used program out of memory to allow more space to the disk cache.
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  2. SWAP

    It is partition is basically a UNIX/LINUX concept in which th e processes are mapped to secondary storage when primary memory is low.Hence if your RAM is big enough the SWAP partition may not be frequently used.

    CACHE

    On the other hand cache is used to store data that has been or will be needed in the near future

    Hopes that helps

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