I have both the 29B and the 29A. The 29B is more capable, more common and in my opinion a better choice. Physically they look almost identical, but there are significant operational differences. According to the manual, the 29A can have a maximum of 16K of buffer memory - this would limit you to 16K or smaller devices (such as 27128), however my 29A came with 64K installed, and can do up to 64K devices (such as 27512). My 29B has 256k of buffer memory, which I believe is the max it can have, and this is enough for pretty much anything you are going to find in a classic computer. I don't use the 29A much - I got it mainly as a spare... but IIRC it either doesn't do automatic device identification, or does it in a more limited way... The 29B is quite good at it. This may be more more a function of the device adapter than the unit itself, which brings us to... Equally important is the device adapter that you get with the unit - you probably want one of the universal "unipak" adapters that supports many different devices. My 29A has a "Unipak2" and the 29B has a "Unipak2B". The 29B/Unipak2B combination can program many more devices. The family/pinout codes for the 29A/2 are only 2 digits where they are 3 digits on the 29B/2B. It would be worthwhile for you to get the device family/pinout code charts for the programming adapters offered with the units and look at the list of supported devices - this will give you an idea of the capability of the unit in question. You will also want to check the RAM installed in the unit, as it may be difficult to add (manuals reference expansion cards). The 29B shows the installed RAM at power-up. For the 29A you need to use the edit command to see how far up in memory you can modify. The 29B has more/better commands and functions as well, although the 29A is still a capable unit. At the same/close price, I'd pick a 29B hands down. A 29A could still be a good choice if you get it cheap enough, and your needs don't require devices larger than it can do - be sure to check the installed RAM and device programming adapter. I have no idea what they are actually worth these days, but FYI - I paid $70 for my 29B quite a few years ago - it came with the Unipak2B and a Gangpak (lets you program up to 8 devices at once - I never use it). I picked up the 29A for $25 a couple of years ago, it came with the Unipak2. I've collected a fair bit of Data I/O documentation in PDF format, including manuals for both units, the programming adapters, and device family/pinout code charts for them. Contact me if you need anything. Dave -- dave06a (at) Dave Dunfield dunfield (dot) Firmware development services & tools: www.dunfield.com com Collector of vintage computing equipment: http://www.classiccmp.org/dunfield/index.html