It's a funny thing about POS, but it's a market that's been dotted with a lot of smaller companies. Yeah, there are some big ones that dabble in the POS hardware over the years--IBM, NCR, Dell, Panasonic etc. And there are a couple of larger software developers, more in the retail market though. As far as the restaurant industry, most of the software developers are NOT giants. The largest among them would probably be Radiant and Micros, and correct me if I am wrong, but even these are not HUGE companies. I am guess this has to do with the way they establish their channels of distribution. POS needs local representation, for the most part. It would a monstrous undertaking for a company to develop software AND have maintain local representation in every state in the union. So, the preferred method for these developers is to establish Value Added Reseller networks. The developers focus on what they need to do, the dealers do do what they need to do, and everyone specializes in their core competency. Because this structure is working, I think it keeps the companies smaller.
What does this have to with you question?
I'm getting to that
Basically, I am not sure there are a lot of resoures dedicated to POS, where you can go by a manual on the basics. The fact that the industry is made of a lot of "smaller" companies, who service diverse and specialized markets, probably has a lot to do this.
I've been saying this for a long time, and it seems to be true (as a matter of fact, if what I am about to say is incorrect, please speak up). People deliberately choose many career paths in life... people study to be doctors, lawyers, network administrators, programmers, auto mechanices. But for whatever reason, VERY few people CHOOSE POS. Instead, they usually "fall" into it. Or it choses them, if you prefer. Most of the people I've known have had some general computer knowledge, and landed a job in POS, and it took off from there. So, I guess what I am saying is at the moment, because it's not a "popular" career path, I doubt your going to find a lot of books dedicated to the topic. Which is ironic, if you think about all the jobs and money in the restaurant industry.
Online articles would probably be your best bet. Do online searches for POS and VAR, and you'll find places like
that will give you some good insight. I am sure someone has written some books on the subject, and those are the kind of places you'll find them.
I used to know of a few more sites, and I'll post them later if I can find the publications I used to have.
Good luck!