The 128K spectrums all had a 48K mode which let you use the old
software without any
trouble. At least that's what I think. I recently set up my +3 for a good game of CRL's
Formula One, and it
crashed a bit even in 48K mode. But I'm opting to think that this is because of the
computer being a little on the old side, since I can't remember having any
trouble with it in it's
heyday.
I always thought (and still do) the 3" diskettes were cool, you could use both sides :-). To my regret the disk drive of my +3 seems to have given up on me, so the biggest feature of the machine is pretty much gone, but even so I'm very glad I still have it around!
In fact, the ZX Spectrum +3 is probably my favourite computer of all time, and I've had a few (ZX Spectrum, ZX Spectrum +, Sinclair QL, ZX Spectrum +3, SAM Coupè (believe it or not!), Atari ST (in many variants), Commodore Amiga (500 and 1200) and the now bog-standard PC)