Memtest is an open source program like Linux
and like Linux - people can take the basic code and alter it to their liking
thats why there are linux versions of memtest
and windows versions
and DOS bootable floppy versions
and bootable CD ISO versions
and running in the backround versions
Just like Mandrake and Redhat, I could bring out a version of memtest tomorrow and call it memtest bozo+
if people liked it, it would survive, if not, it would be replaced by a better version.
86 stands for "x86" type system (not MAC's)
86+ means that the code was updated to allow for new CPU (athlon 64) and much greater amounts of RAM.
the original memtest ceased to be updated in 2002
the latest version (the one noted here is 6-05) is presumably the best - if it works for you.
If you REALLY want to test RAM, you use RST software or hardware ($99 and $200)
http://www.realworldtech.com/page.cfm?ArticleID=RWT041499000000
http://www.uxd.com/rstpro2.shtml