| Eric Doviak | Doviak.net
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Memory Usage:
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MS Windows vs. GNU/Linux
Because R (my favorite statistical software package) is very memory hungry, I need an operating system that makes the most efficient use of memory (RAM). One of the most widely touted benefits of GNU/Linux is that it utilizes memory far more efficiently than Microsoft Windows, but I have never seen that assertion put to the test.
To test the hypothesis, I decided to compare the memory utilization of each operating system on the same computer after a clean reboot. I also decided to start R prior to taking my measurements, so that I would have a rough idea of how much memory is available for my data.
The computer I used for the comparison is a Compaq Presario 1210 notebook (vintage 2001) with 320 MB of RAM and a 1.0 Ghz AMD Athlon 4 processor. The computer has two operating systems: a recently reinstalled version of MS Windows ME and Debian Etch (the most recent stable version of Debian's GNU/Linux operating system).
Because MS Windows ME was released in Sept. 2000, it was designed for computers that are rather "small" by today's standards and therefore utilizes far less memory than MS Windows XP and Vista.
To further increase Microsoft's edge, I disabled the virus scanner in MS Windows, I saddled Debian down with KDE (the most memory-hungry GNU/Linux desktop) and I ran the (bloated) stock Debian kernel (Linux 2.6.18).
Having been given all of the advantages, MS Windows should surely use less memory than GNU/Linux, right? ... Wrong!
Here's a snapshot of the memory usage in MS Windows ME, immediately after restarting the computer and starting the R gui:
Here's a snapshot of the memory usage in Debian, immediately after restarting the computer, starting Emacs and starting R:
To interpret the tables above, compare the 115 MB of "Available Physical Memory" in MS Windows ME to the 140 MB of "free" memory in Debian. Even though we gave Microsoft every advantage, GNU/Linux still uses 20 percent less memory!
More knowledgeable users will also notice that MS Windows ME has used about 317 MB of virtual memory (1240 - 923 = 317), whereas Debian has not used any swap memory at all. (Virtual memory uses disk space to extend the size of physical memory. Swap is a form of virtual memory). In other words, MS Windows' memory requirements are so high that it constantly has to shuffle blocks of data between physical memory and the hard disk. By contrast, Debian hasn't had to "swap out" any data yet.
Finally, it is worth discussing the first two lines of the output of the "free" command. The first line indicates that, out of 322 MB of RAM, 182 MB is in use. The next line subtracts "buffers" and "cached" from the amount of memory in use and tells us that applications are only using 79 of the 182 MB in use.
What is occurring here is that GNU/Linux reads information from disk only once and then keeps it in memory until it is no longer needed. For example, now that you have loaded this webpage, you might copy it into an email message, send it to a friend and then copy the message into one of your mail folders. By reading the data once and keeping it in memory (specifically, the buffer cache), GNU/Linux runs faster because information is only read once.
To make the most efficient use of memory, GNU/Linux uses all free RAM for buffer cache. When programs need more memory, GNU/Linux makes the cache smaller by sending data (that it doesn't currently need) to the swap partition. As we can see from the third line, GNU/Linux is so light on system resources, that it has not had to send any data to the swap partition yet!
| click here to see the Debian GNU/Linux desktop |
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| click here to see the Windows ME desktop |
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