It used a micro cassette for file storage. Anyone who has ever used cassette tape computing will know how horrible this was...but in those pre-disk days it was all we had. At any rate, the tape unit was pretty good in this machine, as it was computer controlled, and acted just like a (SUPER SLOW) Disk drive.
These were discounted and sold through the favorite geek catalog of the 80's, DAK.
The oddest thing about the PX-8 was its ROM based application programs. ROMs were , of course, nothing new, and in fact were a staple of most 8 bit home computers of the 80s. But these weren't ROM-PACKS in attractive plastic cases..there were actual ROM IC CHIPS . You had to remove a panel on the back, pull back the shielding, pry out whatever firmware rom was in there and push in the new one. If I remember right, you could have 2 in at once. I had Basic, CP/M utilities, Wordstar , CalcStar, Scheduler, and dBase II
The feature that killed this innovative , well made machine was its display: 80 column by 8 lines of dim LCD grey on grey text. There just wasn't a lot you could do with it...a valiant effort, but too little, too soon I am afraid.
Here is a 1984 review from COMPUTERS & ELECTRONIC magazine,