There are degrees of compatibility.
I've recently done some experiments with the 244 and other
Tascam Portastudios.
First, the 244's tapes are 100% compatible with the 244, 246 and 234 Syncaset.
Second, the 244's tapes will play back on other more modern Portastudios, such as the 424mkII and 424mkIII, however, there was a design change to the phase relationship of the tracks 1-4, which makes the 244 somewhat non-compatible with these Porta's.
In the old 244 design, the head elements 1-2-3-4 were phase reversed on adjacent tracks in an effort to reduce crosstalk, which it did admirably. This means that head-element-1 is phase reversed with relationship to head-element-2, which is reversed to 3, and reversed again to track/head-element-4.
In practice, for the most part, a 244 original tape will play back on the 424mkIII, UNLESS you have two adjacent tracks (OR ANY R/L PAIR of tracks) that are tracked with the same information, (tracks 1/2 and 3/4, or tracks 2/3 and 1/4 recorded in a mono pair), IN WHICH CASE you'll get a definite phase cancellation of the tracks 1 & 2 and 3 & 4 when played back on a 424mkIII.
I found this information out purely by accident, when swapping test tapes between the 244, 234 and 424mkIII. I was going to post a general topic about the 244's phase relationship between tracks 1-4, and it's issues of compatibility with other Portastudios.
The tests I did were limited to the models mentioned above, as I've not had a chance to test 244 tapes on the 464 or 644.
Keep in mind, however, that the 244-family of devices was designed expressly NON-compatible with commercial stereo cassette tapes, hence the phase reversal of tracks.
The later Portas which were expressly designed to be downward-compatible with commercial stereo cassette tapes is the point in time that Tascam abandoned the head/phase reversal design, and therefore these two types of decks are not 100% compatible.
