Over the years, the main computing paradigm has oscillated between centralized and decentralized computing. The first computers, such as the ENIAC, were, in fact, personal computers, albeit large ones, because only one person could use one at once. Then came timesharing systems, in which many remote users at simple terminals shared a big central computer. Next came the PC era, in which the users had their own personal computers again.

While the decentralized PC model has advantages, it also has some severe disadvantages. Probably the biggest problem is that each PC has a large SSD or hard disk and complex software that must be maintained. For example, when a new release of the operating system comes out, a great deal of work has to be done to perform the upgrade on each machine separately. At most corporations, the labor costs of doing this kind of software maintenance dwarf the actual hardware and software costs. For home users, the labor is technically free, but few people are capable of doing it correctly and fewer still enjoy doing it. With a centralized system, only one or a few machines have to be updated and those machines have a staff of experts to do the work.

A related issue is that users should make regular backups of their terabyte file systems, but few of them do. When disaster strikes, a great deal of moaning and wringing of hands tends to follow. With a centralized system, backups can be made every night, to disk or even tape (by automated tape robots).

Another advantage is that resource sharing is easier with centralized systems. A system with 256 remote users, each with 16 GB of RAM (or 4 TB in total), will have most of that RAM idle most of the time. With a centralized system with just 1 TB of RAM, it never happens that some user temporarily needs a lot of RAM but cannot get it because it is on someone else’s PC. The same argument holds for disk space and other resources.

Finally, we are starting to see a shift from PC-centric computing to Web-centric computing. One area where this shift is very far along is email. People used to get their email delivered to their home machine and read it there. Nowadays, many people log into Gmail, Hotmail, or Yahoo and read their mail there. In addition, many people log into other Websites to do word processing, build spreadsheets, and other things that used to require PC software. It is even possible that eventually the only software most people run on their PC is a Web browser, and maybe not even that.

It is probably a fair conclusion to say that most users want high-performance interactive computing but do not really want to administer a computer. This has led researchers to reexamine timesharing using simple text terminals (now called thin clients) that meet modern terminal expectations. X was a step in this direction and dedicated X terminals were popular for a little while but they fell out of favor because they cost as much as PCs, could do less, and still needed some software maintenance. The holy grail would be a high-performance interactive computing system in which the user machines had no software at all. Interestingly enough, this goal is achievable, although existing solutions tend to be less extreme.

One of the best known thin clients is the ChromeBook. It is pushed actively by Google, but with a wide variety of manufacturers providing a wide variety of models. The notebook runs ChromeOS which is based on Linux and the Chrome Web browser and was originally assumed to be online all the time. Most other software is hosted on the Web in the form of Web Apps, making the software stack on the Chromebook itself considerably thinner than in most traditional notebooks. It turns out that model did not work so well, so eventually Google made it possible to run Android apps natively on Chromebooks. On the other hand, a system that runs a full Linux stack, and a Chrome browser, is not exactly anorexic either.