Wikipedia
Picotux is one of the smallest computers running Linux. There are several different kinds of picotux available, but the main one is the picotux 100. It is 35 mm × 19 mm × 19 mm and just barely larger than an 8P8C modular connector. Two communication interfaces are provided, 10/100 Mbit/s half/full duplex Ethernet and a serial port with up to 230,400 bit/s. Five additional lines can be used for either general input/output or serial handshaking.
The picotux 100 operates a 55 MHz 32-bit ARM7 Netsilicon NS7520 processor, with 2 MB of Flash Memory (750 KB of which contains the OS) and 8 MB SDRAM Memory. The operating system is μClinux 2.4.27 Big Endian. BusyBox 1.0 is used as main shell. The picotux system runs at 250 m A only and 3.3 V +/- 5%.