Back in the early 1980s, when the world was young, I had more hair, and Lotus 1-2-3 ran just about as fast on a 286 processor in character mode as Excel does now on a Pentium under Windows/NT, the toughest auditing problem in a big spreadsheet was tracking down circular references. (Okay, I admit it … I caught myself saying to a friend the other day, about rap music, “It all sounds the same to me.” I’m starting to geeze.)
Anyway, you’ll recall that with a circular reference, a cell’s formula refers to its own value, which means the spreadsheet never yields the same result twice. The simplest example: the formula =A1+1 in cell A1.
In some situations, for example simulations and formulas that require recursion, circular references can be useful. Most of the time, though, they give you meaningless results.
Here’s another example of a circular reference: “Client/server systems cost more than mainframe systems.”
You’ve heard this repeatedly from authoritative sources in the industry that charge so much for advice they must be right. Except they’re demonstrably wrong, because this calculation involves a circular reference. Don’t believe me?
How many times have you heard this semi-true statement: “The mainframe won’t go away, but it’s role will change. It will become the biggest server on your network.”
Okay, let’s see. Client/server systems cost more than mainframe systems, and mainframes will be servers in client/server systems. Put these two facts together and you’ve proved that client/server systems that use mainframes as servers cost more than themselves!
Ain’t logic a wonderful thing?
Want more proof? I’m glad you asked. Imagine a small system … it has ten tables, five concurrent users, no more than a thousand records in its biggest master table, and handles about one transaction a minute. Which will be more expensive to develop and maintain: a mainframe, COBOL/CICS/3278 system, or something you build in Access, Paradox, Visual Basic or Delphi on a small PC network? Hint: the word “COBOL” shouldn’t appear in your answer.
Now imagine an airline reservation system: millions of records in its main tables, thousands of transactions per second, and oodles of concurrent users. (An oodle is somewhere between a whole lot and a bazillion.) This time, yer basic COBOL/CICS/3278 system wins.
If you’re so inclined, imagine a graph. The y-axis is cost, the x-axis is a composite size/compexity index. When x is small, non-traditional architectures cost much less than their mainframe/terminal-host equivalents. The line representing mainframe/terminal-host costs increases with size more slowly than the line for non-mainframe systems.
Somewhere, the lines cross: “client/server” systems – actually, systems built with a multitier application partitioning model, non-mainframe servers, and GUIs – sometimes cost more, sometimes cost less than “mainframe” systems (those built with a single-tier application partitioning model, mainframes as the host, and a character-mode user interface).
This isn’t a one-size-fits-all situation: the optimal architecture depends on circumstances. Big batch jobs require big mainframes. Kludge together a solution based on too-small servers and your costs go up. Talk about blinding revelations.
And the circumstances are far more complicated than most pundits (but not yours truly) would have you believe: it’s a mix ‘n match situation. “Client/server” vs “mainframe” tangles a bunch of separate threads. Next week we’ll explore this subject in detail, untangling these threads and using them to cross-stitch a portrait stunning in its beauty and complexity (help! The metaphor police are after me!)
Strictly speaking, the term “client/server” refers to an application partitioning model. In client/server applications, developers separate applications into multiple, independent, communicating processes. They can all run on a mainframe. They can all run on a single personal computer. They can run on a server, or some can run on each.
Of course, we’ve been doing this, in limited fashion, since the invention of operating systems and subroutine libraries. Which means the opposite of “client/server” isn’t “mainframe”.
It’s “bad programming”.