The borders between different types of portables, laptops/notebooks, sub/mini-notebooks, palmtops, PDAs/HPCs are rapidly changing. Weight is becoming less. Storage capacity increases.
Weight greater than 4.0 kg (9 lbs). Features like a PC, but in a smaller box and with LCD display. Examples: lunchbox or ruggedized laptops (e.g., BSI(http://www.bsicomputer.com/))
Weight between 1.7 and 4.0 kg (4 to 9 lbs). Features custom hardware and usually a special CPU. Examples: HP OmniBook 3100, COMPAQ Armada 1592DT. The terms laptop and notebook seem equivalent to me.
Weight between 1.3 and 1.7 kg (3 to 4 lbs). Features: external floppy drive, external CD drive. Examples: HP OmniBook 800CT, Toshiba Libretto 100, COMPAQ Aero, SONY VAIO 505.
Weight between 0.7 and 1.3 kg (1.5 to 3 lbs). Features: proprietary commercial operating systems. Examples: HP200LX.
Weight below 0.7 kg (1.5 lbs). Features: proprietary commercial operating systems and often non-Intel CPU with commercial operating systems like PalmOS, EPOC32, GEOS, Windows CE. Examples: Newton Message Pad, Palm III (former Pilot), Psion Series 3 and 5, CASIO Z-7000.
Though in my opinion related to the topic, these devices are not covered in this text, yet. For general information about Embedded Systems, see http://www.embedded.com (http://www.embedded.com). For Linux information, see ELKS(http://elks.sourceforge.net/) and the uCLinux(http://www.uclinux.org/) project. And my page about Linux with Infrared Devices.
see iX(http://www.heise.de/ix/) 7/1999 p. 63, Code Warrior