You'll find mainframes in many/most large older (founded before 1990) organizations but almost nowhere else. There doesn't tend to be a lot of detailed informa

You'll find mainframes in many/most large older (founded before 1990) organizations but almost nowhere else. There doesn't tend to be a lot of detailed information publicly available for proprietary enterprise products generally. This is partly because that's the way many companies prefer it (i.e. trade secrets and NDA's) and partly because they just aren't of general interest to hobbyists/hackers/smaller customers. In addition to the lack of information, mainframes also have significant physical/electrical/cost constraints which further limits interest in terms of actually owning one... which would be a driver of interest. Compare this to your typical PC/mobile device which fits on/in a desk/lap/pocket, is practically free in comparison, has a deluge of information available everywhere and is actually useful to most people in everyday life. About the only thing a mainframe really gets you is reliability in a monolithic device which from a cost/benefit standpoint isn't worthwhile for most customers and can be approximated via other means. I've been inside many organizations that run mainframes and if you're not on one of the mainframe teams, which tend to be tiny relative to other IT groups, it's pretty much plumbing as far as the rest of the organization is concerned... which is the point.