This is my new toy: the Atari Portfolio palmtop from 1989. It is quite big (like the VHS casette) and it is somewhat limited (a 80086 processor, a 128 kB of RAM and a 40×8 characters display) but all of these parameters were OK when it was new. The screen has no backlight. I uses three AA batteries so it can work couple of weeks on single set of batteries. It runs a DOS 2.0-like operating system.
Being the one of the first (if not the first) palmtop computers it is filled with propietary technologies (RAM expansion cards and expansion modules)
but it was necessary at the time (there was no standard for such things). It also includes some build-in application (a Lotus123-compatible spread sheet, a plain text editor and a calendar program with alarms).
The main limitation is the size of its memory: 128 kB is divided between data storage (RAMdisk, usually 32 kB) and the actual operating memory. The expansion (battery-backed) cards can be sized from 32 kB to 512 kB (I have 32 kB one). It means that only relatively small programs can be used here. My ddfor software does not fit into the 32 kB when compiled by my favorite DOS compiler. I have had to compress the executable (both the pklite and the lzexe works well).
There are no speed issues: build-in applications starts under one second and they are very responsible. Big slow programs (like the Gnuplot) simply don’t fin into the memory. The computing speed (when using the ddfor is similar to the HP 95LX).