only dif between xp and mp is xp MEANT for single cpu system, mp MEANT for smp system
...but it really doesnt matter, just amd labels mp's as "certified" for smp application, but they are the same core (you caneven mod xp's into "mp's"...in that you can run them in smp systems just fine should they not work without the mod)
..and now i forgot what your question was lol...scrollig dwon to read...
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recently there have been developments within the athlon xp though...there the 2 different cores with 2 in one subsystem..
1. palomino
-0.18micron
-not a die hard overclocker (minus the xp1600 miracle chips)
2.a. Thoroughbred A
-0.13 micron
-semi good ocer (good to abot 1.8-1.9ghz ...MAYBE 2 at most)
2.b. Thoroughbred B
-0.13 micron
-AWESOME ocer (1.8-1.9 MINIMUM from xp1700+ dated 0302 or later with stepping JIUHB ; xp2100+ AIUHB is another good one...2-2.3ghz usually)
to distinguish between tbred a and tbred b, look at stepping
if XXXXA then tbred a, if XXXXB then tbred B
also, cpuid code of 680=tbred a, 681=tbred b (but that doesnt help much when you want to identify it BEFORE you buy it lol)
for the lower models (xp1700+ and xp2100+) the last 5 letter/number sequence on first line should be DUT3C (tbred b) , not DLT3C (tbred a)
//edit
forgot to address another question heh
id still go for amd (cuz its a bit cheaper still...especially if you are ocing)...
but if you are not ocing, probably still go for a higher model amd
but there are also good ocing p4's as well (p4 2.4ghz SL6RZ is a realy nice one)
depends on ocing (or not) and budget