Salix Xfce will actually run decently (with a full desktop) on a Pentium II or thereabouts, the main problem is sane settings for various things.
- Outline window resize is the single most important setting. Temporarily freezing the screen is a small price to pay, compared to the number of refreshes you'd be dealing with otherwise.
- Compositing managers may actually help a bit by further reducing refreshes, *if* you use outline resize. Opaque resize with compositing is often slow even on modern computers.
- Application choice is important, but less important than you'd think if you have enough RAM and enough patience. Sometimes things are counterintuitive, e.g. LibreOffice Writer works better than Abiword because Abiword uses smooth scrolling. OTOH, KDE applications (any of them!) will barely work at all, at least on Salix. The best browser is probably Opera or something webkit-based, e.g. Midori; note that Webkit-based browsers will be slow unless you disable certain shadow effects (see here
- Be careful with xorg.conf settings. Some older video cards and/or drivers are really finicky, and will crash your desktop with custom settings. Xorg autodetection is usually good enough. The exception is cards that prefer 16-bit color depth, since current Xorg versions usually default to 24 - that has to be changed in xorg.conf if you want reasonable desktop performance.
- Tuning swappiness down actually doesn't help that much. Depending on the computer, though, zram may make a big difference. For hard disk swap, you might want to use a file instead of a partition; that way you can resize it if needed. (The latter holds especially true for pre-ACPI machines, and others that can't hibernate.) Tuning swappiness up
may actually be helpful, since it would let more RAM be used for filesystem cache, but I haven't tested it enough to be sure. Make sure you actually have enough swap, since you definitely will be swapping.
- I don't think the noatime mount option helps much, but it certainly doesn't hurt.
- Using writeback mode for ext3/4 might help performance, but risks appending garbage to edited files (instead of the data you saved!) if an unexpected shutdown occurs at an inopportune time.
- Things like drive IO queue length, drive readahead sectors, VFS cache pressure, and other obscure tweaks don't help (and probably hurt). In general, I find that the more obscure the tweak, the less likely it is to be helpful on old hardware.
- 2.6 kernels perform far better than 2.4 kernels. Not sure about 3.x kernels, I haven't gotten to try one on my Thinkpad yet. The BFS CPU scheduler may be helpful.
- Above all, don't expect miracles. A Pentium II will slow down perceptibly when rendering large web pages, installing updates, etc.; that doesn't mean it will be unusable. Expect it to be fairly slow, and you won't be put off when it performs poorly (and may be pleasantly surprised when it performs well).
Aaand that's pretty much all I've got for using Linux on old desktops. I really should bring out the Thinkpad again, when I have the time...