Diskless workstation
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A diskless workstation is a workstation or personal computer without any means of non-volatile storage (hence "diskless"); although non-volatile solid state media is not a true "disk/disc". Not to be confused with terminals or cut-down PCs acting as such, a diskless workstation is intended to run in a fully "stand-alone" mode after the initial boot phase. It thus runs a full modern operating system from its own local RAM. Such computers are sometimes known as Net PCs.
[edit] Bootstrap operation
The operating systems for these computers are loaded from a server, using the BIOS in the computer to locate the startup media, and begin the bootup process. This is called booting from the network, or having a network boot. Other sources may be used for the OS image, such as removable storage (such as a USB flash drive, as well as bootable CDs containing an OS (such as Knoppix).
Needless to say, at least some parts of the OS have to be loaded directly into the PC's memory, part of which is configured as a RAM disk. Bootstrapping such a PC usually involves a two-step process, in which a RAM disk is created, DOS is loaded, and then the OS image is fetched and loaded into the RAM disk.
A simple Network booted system can be constructed by launching DOS from locally attached floppy disk and using NetBEUI protocols to access a network "share" containing the OS Image. The "professional" version is performed via TCP/IP (and the BOOTP protocol, the precursor of DHCP). This was originally only available from a special "BOOT ROM" chip option fitted to the Network card, however BOOTP protocols are now embedded directly into the BIOS of many modern Motherboards and Network Cards).
Any applications that the user might wish to use also have to be pre-installed (so that they loaded alongside the OS image).
After loading the OS, control has to be passed from the "bootstrap" program to the OS itself. This is all but impossible with modern Microsoft Operating Systems (such as NT, 2000) so historically diskless PCs have been limited to Unix- or Linux-based systems (although Windows 98 SE has been used with some success, and, in theory at least, Windows XP is supposed to be compatible with network booting).
[edit] Advantages
The major advantage of a diskless PC is that any system changes made during operation (due to user action, worms, viruses, etc.) are wiped out when the power is removed. This allows use in public access areas (such as libraries) or in schools etc. where users might wish to experiment or attempt to "hack" the system.
This makes the concept very popular with major corporations (who wish to retain 100% control over their employees' use of computers). However such corporations tend to implement remote terminals (using Microsoft Windows Terminal Server or other such software), since much lower specification hardware can be used for the client (which essentially acts as a simple "window" into the central server which is actually running the users operating system as a "session").
Another example of a situation where a diskless workstation would be useful is in a possibly hazardous environment where computers are likely to be destroyed, thus making the need for inexpensive nodes, and minimal hardware a benefit.
Diskless machines also consume little power and make little noise, making them ideal for some computer cluster applications.
[edit] Disadvantages
The fact that nothing is stored locally can also be a major disadvantage. All work in progress has to be saved to some external store, such as a network share or USB flash drive, etc. This can cause problems later, when a user returns and cannot find his or her work.
