The successor to the Model III was the TRS-80 Model 4. It had faster Z80A 4 MHz CPU, a larger video display 80 columns x 24 rows, bigger keyboard, and could be upgraded to 128KB of RAM. The Model 4 was fully compatible with Model III software and industry-standard CP/M applications software. A diskless Model 4 (with 16KB RAM) cost $999, with 64KB RAM and one single-sided 180K disk drive $1699, and two drives $1999; an upgrade for Model III owners cost $799 and provided a new motherboard and keyboard. The new computer used exactly the same all-in-one cabinet as the Model III, but instead of the silvery-gray plastic formerly used the Model 4’s case was off-white.
The Model 4’s first appearance in the Radio Shack catalog read as follows: “Yes, it looks like a Model III, but it’s much much more. Compare the price and features of our amazing new Model 4 to any other computer in its class. You’ll find that for power, versatility, and convenience it is a true breakthrough. To add the same features to other computers, you’d have to pay a whole lot more”.
| Manufacturer | Tandy / Radio Shack | CPU | Zilog Z80 @ 4 MHz |
| Year Introduced | 1983 | RAM | 16KB-64KB |
| Introductory Price | $999 (16KB) $1,699 (64KB, one floppy) | Storage | Cassette Optional 5.25" floppy disks (178KB) |