old CDS modem

Found an old modem that I forgot I owned and was just wondering a few things. First, it's a Concord Data Systems 224 ARQ/Autodial that I now remember was in tow by a 3B2 I picked up a while ago. Anyway, it's rather heavy (humongous hat sink on back) so i opened it up and began to think that the innards seemed a bit complicated for a 'modem.' OK, I'll admit it, I was 11 years old when these things would have been in use, but I have other modems from the peiod ('85-'86) that aren't nearly as complex. It's about the size of a large book and has three levels of circuit boards with a Z80 CPU, an SIO chip, and memory chips (one says "zeropower (tm) ram" on it and "DO NOT DISPOSE OF IN FIRE!!!!") on one level, Intel 8031 series chips on another and who knows what on the bottom (haven't taken it all apart yet). Not to mention the 32 dip switches (all off) and the 23 led's on the front. To make a long story short, what did/does this thing do that a regular modem of the time didn't do? Thanks, les