| The word mainframe is often used ambiguously. In my experience it could mean: System Z - as I understand it, this is descendant from IBMs earliest computers like System 360. Typically apps are written in COBOL, PL1, tied together with JCL. “Newer” apps use DB2, but there are older non-relational databases as well. System P - an IBM alternative server architecture based on the Power chipset. I think these mostly run UNIX, but I’ve never been hands on. AS400 - technically an IBM minicomputer, but similarly esoteric with a bespoke OS and some nifty functionality for business apps (very SQL centric). HP Tandem - traditionally used in high availability transaction processing applications. Others? I think most of the other surviving old stuff is basically UNIX Typically people are thinking of System Z. I think both the inertia and scalable ACID explanations are relevant. That said, I’m not sure how DB2 on System Z compares to say Oracle RAC. |
While there's technically overlap in performance between the lowest spec Z and the higher end P, and these days lots of performance overlap between P and X ranges, P-series is called "midrange" by everyone I've every met.
The Power hardware has been the basis for both the AS-400 and P-Series/AIX line for a long time now, although you can buy p-series with linux too.
As an asside, AIX, with the exception of its volume manager which irks me deeply, is an incredibly usable Unix.. I mean you can really manage the whole thing via the SMIT UI without ever touching the command line. Not my preference, but you can. Some things, like cpu usage reporting are still better on AIX ( core utilisation via hyperthreads for example )
I'm still not a fan as such, mostly I'm annoyed by how good it is, but credit where credit is due.
Of course there are some people, (usually older but not always), who will call any server, or anything in a server room "the mainframe", in the same way the any desktop tower gets called "the cpu" (technically correct via some broader definitions but still..), or they'll call whichever office app they primarily use as "Microsoft", and of course you need to take that into account when communicating with people, the the incorrect usage of mainframe seems pretty rare these days just because mainframes themselves are rare.. and people in businesses who have them generally can distinguish.