the best is windows xp server
Windows Small Business Server 2008 is the most current, and popular server operating system. Dell and HP both manufacture servers with this software, and have staff available to help if needed. Another option would be to use a hosted server from a local company or a cloud-based server from a company like www.rackspace.com.
Contact your local office supply store for comparison of small business servers. The windows small business server website can also offer solutions for small business and prices for their services.
You can purchase servers at any of the office stores. Some of those office stores that you can purchase the servers at are Office Max, Office Depot and Kinkos.
Slax is small, portable, and fast Linux operating system. It refers to itself as "your pocket operating system". It is a Slackware-based bootable CD designed with modular approach.
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Certain versions of the Linux operating system can be installed on and booted from a memory stick.
Lots of Linux distributions, and other free operating systems, will fit on a 1 GB hard drive. The real question is what you are trying to accomplish with said operating system. For a small desktop system, look at: Puppy Linux Damn Small Linux Feather Linux QNX (free for personal use, partially open-source) KolibriOS AROS Syllable For a server, almost any server edition of Linux will work, such as: Ubuntu Server Fedora Debian (do a netinstall, and install only the parts you need) With some tweaking, you could probably also fit a standard Debian, Slackware, or Gentoo. Although I wouldn't recommend it, you could use the same method for putting Ubuntu on a 1 GB flash drive for a hard drive as well.
Apple servers differ from Windows servers in a few small ways. They first off use completely different operating systems. They also have different interfaces for use.
Basically, you shut the computer down. Procedure for that depends on the specific operating system. Operating system is what makes a computer do things. Even the thing the loads the main operating system for a given computer is a small operating system in itself. For example, the thing that loads Windows or Linux up is called BIOS, and that stands for Basic Integrated Operating System. Once you exit all the operating system(s) you may as well shut down the machine (if it does not shut down by itself.)
usually updates the operating system in small ways, normally small changes to it
This depends on the context of the questions your asking. A network computer would be considered any computer or operating system on the network that is addressable. In most small networks though, a small computer is often used as network server for storage or other puroses. Switches are used for connectivity in a wired network to provide connection from client to server. The types of networks that use moderately capable computer are quite small though often consisting of merely 15 computers or less, which in terms of networking is very small.