The SX/DX 64 is the "laptop version" (though hardly portable) of the C64. This computer has a built-in 5" color screen (just about enough for the eyes), a detachable keyboard with new functions, and one or two 5.25" floppy disk drives (the famous 1541), depending on the model.
The DX-64 and the SX-100 (SX-64 with black & white monitor) were first announced in January 1983 but the SX-100 never made it to the shelves and was replaced by the SX-64 later that year.
One important feature is that the SX/DX-64 lacks a cassette interface ! People who upgraded from the classic C64 couldn't play their games stored on tapes !
Some programs that used the tape buffer for storage (of sprites say) had problems too.
The cartridge slot is found on top of the case, and there is a sound speaker inside the unit (unlike the C64).
The DX-64 has the same characteristics as the SX64 except its two 5.25" floppy disk drives instead of one. A very small quantity was produced. It was probably never sold but only used by Commodore insiders.
The SX64 and DX64 computers never had success, probably because of higher selling prices, but were known as the world's first color portables.
The SX64 was not the only machine that Commodore made in this chassis, there was also the SX500, which was an Amiga in the SX case (see 'More pictures').
I want one. I am willing to pay up to $100 for it. Let me know!