From LQWiki

Dumb Clients, a type of terminal, refer to a computer-like devices with only the most basic functionality. They are not really dumb, but are designed as simply as possible as their only purpose is to connect to a much more powerful, 'smart' computer, also known as the terminal server.

One of the characteristics of 'dumb clients' is that without a server to connect to, they are essentially useless.

In the LTSP world, a dumb client might be a 5 or 10 year old computer, probably with some unneeded hardware removed. Or, it might be a new computer designed for the single task of connecting to a server over the network.

It is not possible to have a monitor extension cord run 50 meters, or plug 30 monitors into a terminal server (the 'smart' computer). While this is certainly not the case, you might imagine that the use of dumb clients allows users to access the main terminal server, as if their monitor, mouse, and keyboard were literally plugged in directly. In reality, dumb clients act as an intermediary between the main terminal server and the user, keyboard, mouse, and monitor.

While individual configurations vary, the following is a slightly more technical description of how a dumb client functions. Upon power on, a dumb client sends a message out over the network, essentially asking "Who am I?" using technology such as PXE or EPRom. The terminal server responds, and loads into the dumb client's memory a very small image of the linux kernel. The kernel has been preconfigured, so that the only thing it does is connect over the network to the terminal server, and open an X-windows session. This X-windows session appears on the dumb client's monitor, but is really running back on the terminal server. When the user presses a key, the dumb client sends information about this keypress to the terminal server, which updates the x-windows session, which is redisplayed on the dumb client's monitor, showing the results of the keypress. From the user's perspective, this keypress occured on his 'computer' but in actuality it occured on the terminal server.

Old Computers configured as Dumb Clients

Any Pentium class computer (sold as far back as 1993) has sufficient hardware to act as a terminal. Very often, unnecessary hardware is removed, which includes the hard disk and modem. One goal is to reduce moving parts to a minimum, and a terminal often has only a small fan to cool the CPU, or even no fan. Sound cards, Floppy Drives, and CD-Roms may or may not be present; this depends largely on the needs of the users.

New network cards are often necessary, as old computers lack network cards or their network cards do not have recent technologies such as PXE.

Schools often have older, otherwise obsolete computers that can be used as terminals, and can often request additional computers from the parents, local businesses currently upgrading, or other local organizations. With the help of parent volunteers, entire classrooms or even schools can be fitted with computers for no more than the cost of the more powerful terminal servers.