Sharp's Zaurus SL-5600 pioneered embedded Linux techniques worth emulating, and others worth improving upon, writes Peter Seebach in a DeveloperWorks article examining one of the first Linux PDAs. Seebach describes the SL-5600's hardware, Linux port, boot process, filesystem layout, and account management strategies, good and bad.

Sharp shipped the Zaurus SL-5600 in March of 2003, about two years after the original SL-5500 and SL-5000D developer editions. The SL-5600 featured more Flash, less RAM, a bigger battery, better keyboard, and other changes reflecting user and market feedback, Seebach says. One key change was storing user data in non-volatile memory, to avoid data loss associated with complete battery drainage.

The SL-5600 uses a non-standard boot process, with several run levels adapted to the unique design requirements of PDAs (i.e., no console, and little networking). It also has a strange filesystem layout, with /etc/ symlinked to /home/etc. This was done in order to simplify backups, Seebach conjectures.

The SL-5600 additionally has a non-standard user account system, in which the GUI runs as the root user, while many applications run as a “zaurus” user. This is good, in that PDA users typically don't want to log in, but bad in that standard Linux administration actions, such as adding new users, can be problematic.

Seebach's article discusses many other architectural features/bugs of the SL-5600's unique architecture. The full story can be found here.

 
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