Time-sharing

Time-sharing usually refers to the shared simultaneous use of a large computer by several users using small computers or terminals, but the term can be expanded to any shared or multi-user use of computer hardware.

Server-based time-sharing

This is the oldest type of time-sharing originating from the decades when computers were very expensive. However, it has recently returned to prominence of broadband Internet connections: ?cloud computing, ?software as a service, etc.

The difference is that while the original form represented a more efficient use of computing resources (and a more immediate, interactive access to those resources), the current trend is more closely connected to corporate interests and "intellectual property". Software that depends on an external server cannot be pirated as easily. The network bandwidth requirements often make the use of this kind of software consume a lot more energy than running equivalent software locally.

Distributed public computing

This is the idea of using the spare computing power of small computers to assist in a large-scale computing task – essentially the opposite of server-based time-sharing. Seti@Home was an early prominent example of this.

This was a particularly relevant idea when a lot of users had powerful personal computers that consumed a lot of energy even when running idle, but nowadays more care is needed when assessing such projects.

Sharing of computers

This refers to the use of a single personal computer by several people. This may be a computer shared within a family or a community, or a public computer/terminal located in a place like an Internet Cafe, a computer classroom or a public library.

Currently, the industry pushes everyone to own a personal computing device (especially a smartphone), which is causing a huge environmental impact which is further multiplied by ?planned obsolescence. This is accompanied by a psychological impact which is arguably more negative than positive especially if "online" becomes the default state of mind. Revitalizing of computer sharing might help tremendously with these problems.