The Model III was basically a Model I with some significant differences. First of all, the keyboard, screen and disk drives were all together. This made the machine more reliable. It also had an improved ROM with some bug fixes in the BASIC and the Z-80 CPU ran a little faster. The biggest reason that Tandy Radio Shack started selling this machine though was because the Model I did not pass FCC tests at all -- producing all kinds of electronic noise because it wasn't shielded at all.
Bob Bauer on Saturday, February 20, 2010 I owned the two-drive version with 64k of ram. It was an amazing improvement from the Model 1. I wrote and used both a word processor and a spreadsheet application in Basic on it. The computer and software were better than a typewriter - but not much better.
Darren Fath on Sunday, November 02, 2008 The first computer I had at home was a Model III with cassette storage and 16KB of Ram (upgraded eventually to 48KB)
I never bought the very expensive floppy opption, opting instead to buy an Apple II clone in 1986.