This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
The //c and IIc+ are compact 'luggable' versions of an Enhanced //e, with many built-in 'cards'. Included are 2 serial ports, a mouse port, a disk port and 128K of RAM. Support for the original Apple casette tape I/O is gone. The / /c has a built-in 5.25" drive while the IIc+ has a built-in 3.5" drive. The IIc+ has a built-in accelerator that runs at 4 MHz (vs. the //c's 1MHz) making it the fastest Apple II as well as faster than any of the A2 clones. (To boot your IIc+ at 'regular', 1MHz, speed, include the Escape key in the usual boot keypresses-- i.e. OpenApple-CTRL-ESC-RESET.) The IIc+, which was introduced after the IIgs, also allows daisey chaining the GS Apple 3.5" drive along with 5.25" drives. The //c and IIc+ run just about all of the DOS 3.3, ProDOS, "128k" software, etc. that an Enhanced //e runs plus the few //c-only software releases. However, the use of certain locations for storing system variables and ROM differences means that //c series machines will not run a number of old games designed for the ][ and ][+ which the IIe and IIgs will run. Even though //c machines don't have slots, you can still add extra memory (there's room under the keyboard) and a hard drive (through the disk port-- a bit slow by ordinary standards, but usable. Hard to find though.. Was made by Chinook). There is also a for-//c "D" version of MockingBoard you can plug in to get much improved sound and music from software supporting the board, and a module you can attach to convert output to RF for using a TV as a monitor. Recommended configuration: A composite color monitor which can display decent 80-colume text, 1 MB RAM, and, maybe, a hard drive. For the //c, add a second 5.25" drive; for the IIc+, add a second 3.5" drive and two 5.25" drives. --Dan DeMaggio, Rubywand