XP pro (x86) running on a 2008 Acer Aspire One ZG5 netbook (Intel Atom N270 @ 1.60GHz)
Upgrades : 1.5Gb RAM, Ralink 802.11n Wifi card, 64Gb ZTC Cyclone SSD for OS, 256Gb SD card storage expansion for programs, documents, etc... and another 128Gb micro-SD card for swap, downloads, etc... And a 9 cells battery that gives roughly 10 hours autonomy for office work, music listening (wifi turned off), and between 5 to 7 hours with wifi turned on...
Genesis and PC Engine retro gaming included !
;p