The "personal computer" model scales better than the "terminal" model

Summary

In an aside in a recent entry, I said that one reason that X terminals faded away is that what I called the "personal computer" model of computing had some pragmatic advantages over the "terminal" model. One of them is that broadly, the personal computer model scales better, even though sometimes it may be more expensive or less capable at any given point in time. But first, let me define my terms. What I mean by the "personal computer" model is one where computing resources are distributed, where everyone is given a computer of some sort and is expected to do much of their work with that computer. What I mean by the "terminal" model is where most computing is done on shared machines, and the objects people have are simply used to access those shared machines. The terminal model has the advantage that the devices you give each individual person can be cheaper, since they don't need to do as much. It has the potential disadvantage that you need some number of big shared machines for everyone to do their work on, and those machines are often expensive. However, historically, some of the time those big shared servers (plus their terminals) have been less expensive than getting everyone their own computer that was capable enough. So the "terminal" model may win at any fixed point in both time and your capacity needs. The problem with the terminal model is those big shared resources, which become an expensive choke point. If you want to add some more terminals, you need to also budget for more server capacity. If some of your people turn out to need more power than you initially expected, you're going to need more server capacity. And so on. The problem is that your server capacity generally has to be bought in big, expensive units and increments, a problem that has come up before. The personal computer model is potentially more expensive up front but it's much easier to scale it, because you buy computer capacity in much smaller units. If you get more people, you get ea...