Full support for WinXP ended a few years ago. Microsoft has still been distributing Critical Updates for malware known to be in circulation and causing "significant" damage, but there are no optional updates, and no protections against the infamous "bit rot" that has a tendency to cause declining reliability of the OS itself. (In (over?)simplified terms, new aps may demand OS updates that won't happen for XP, and if the new stuff is marginally compatible with the old system, the whole system eventually gets scrambled.)

A final "SP" update, consolidating previous patches, was released some time ago, and NO OTHER PATCHES are being provided unless that one is installed. The SP patch package has been available, for those who don't have it, to bring WinXP up to "maintainable" status; but I don't know how readily it remains available.

The primary reservoir of infected WinXP machines appears to consist largely of those who have never, or rarely, installed any security updates, or used AV protections. Microsoft estimates that 50% - 60% of those machines are "pirated" copies that have never been able to get updates for that reason.

Even with all patches, WinXP has a fairly large number of vulnerabilities that were not patched when the weaknesses were discovered based on their difficulty of use, and the likely amount of damage that could be caused by exploiting them. Newer malware methods have made some of these potentially "more useful" to maleware distributors, and hence more dangerous to users.

RAM chips suitable for upgrading most WinXP machines were not particularly expensive the last time I looked for some, but may be hard to find now. For newer machines the RAM chips are fairly generic, but some WinXP and earlier machines were picky about check bits and error correcting features, as well as speed. Since you need to "install in pairs" you may have to take out two and put in two (or 4) bigger ones. As noted, most WinXP processors will be at clock speeds slower than recommended for some current software, so there's little you can do to make a useful improvement that will be cheaper than just replacing the both the machine and the OS.

It's unlikely that anything more than about 1 GB RAM will really help most users of WinXP, although I don't recall what was spec'd as the maximum installable. More RAM would let them load more into RAM, but as the amont loaded increases the overhead to keep track of what's-where results in a phenomenon called "page flop slowdown," so excessive amounts of RAM are self-defeating above a certain point. For WinXP, on most machines, the maximum installable was quite a bit more than the optimum amount to install.

John