The Model 4P was the transportable version of the Model 4.
Apart from the case and display sizes, technical features were almost identical to the Model 4's. The dual half-sized floppy drives were still single-sided versions but the keyboard, which slided underneath the computer, was far better than the one of the desktop version.
The external floppy drive connector was removed, as well as the Model 3 ROM, but a ROM image could be loaded from diskette to run Model 3 programs. An optional 300-baud modem could be also installed into the machine.
Very late models had double-sided TEAC drives.
Further information from Greg Trotter
I used a Model 4P for many years. It was pretty much identical to the Model 4 in functionality, except for:
- Portability, of course
- No Model III ROM (but you could load an image of the ROM into the RAM and reboot, giving perfect compatibility)
- It did have a modem card slot, except that the card edge provided power only; the outward face of the card had a short DC-25 serial cable, just long enough to get to the serial port of the 4P.
- There was no cassette interface on the 4P.
- The keyboard was indeed superior; I liked it better because it was corded and could be moved to any angle.
Of course, portable just meant "easier to transport." The entire unit weighed about 28 pounds, if I remember correctly. I lugged it through airports, and it fit quite comfortably in the overhead bin.