HP 200LX

The Hewlett-Packard 200LX is a tiny portable computer from 1994 that runs MS-DOS. It has a 640x200 pixel 4-shade greyscale LCD, 7.91MHz 80186-based system-on-chip and 2MB of RAM, as well as a PCMCIA slot (Type II, 5V at 150mA maximum), an infrared port (SIR), and a full RS232 serial port. It's almost fully compatible with PCs of that era, so you can run various programs on it (and even games). My 200LX also has a 32MB CompactFlash card in a CF-to-PCMCIA adapter.

The built-in graphical software is quite nice to use and includes applications such as: Appointments (calendar and to-do list), Phone Book, Note Taker, Memo, Lotus 123 (spreadsheet), HP Calc (RPN scientific calculator), Pocket Quicken (finances), Filer (file manager), World Time, Data Comm (serial terminal), Database, Stopwatch, …

The RAM is divided into 640kB of program memory and the rest is used as a ramdisk for storing files. It's a good idea to make regular backups of the internal ramdisk, since it loses all data when the batteries run out!

The HP 200LX runs on two standard AA batteries (plus a CR2032 for memory backup). I've had good experience using rechargeable NiMH AA batteries (Sanyo Eneloop) — the battery life is great, but they take a long time to charge due to the way charging is implemented on the HP 200LX (it only trickle charges them, which is very safe, but slow for the typical capacities of modern NiMH cells).