Multiseat

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A four-head multiterminal.

A multiseat, multi-station or multiterminal configuration is a single computer which supports multiple users at the same time. The configuration typically consist of one monitor, keyboard and mouse for each user and may include headphones for some users.

1 Why do it?
2 Requirements
3 How to do it
- 3.1 Using Linux
4 Case studies
- 4.1 Paraná Digital project
5 See also
6 External links

[edit] Why do it?

With the increasing capacity of processors and memory, computers can now perform significant numbers of tasks simultaneously without slowing down. However, using standard computer configurations, only one user is able to use the computer at the same time, limiting the effectiveness of the system as it remains idle most of the time. With a multiterminal, a lot of users can share the same computer, so more of its total capacity is going to be used. For example, if someone is just using a web browser or word processor, no one else can use the computer and 90% of the system's resources may be idle - but with multiterminals, other people will be able to use the otherwise idle resources. However, if someone is using all of the system's resources (playing an intensive computer game, for example) the other users will have a very slow system.

Multiterminals are also more cost-effective: it is not necessary to buy separate motherboards, microprocessors, RAM, hard disks and other components for each user. For example, buying one high speed CPU usually costs less than buying several CPUs of slower speeds.

[edit] Requirements

Each monitor will need to be connected to a graphics output. Some video cards have multiple outputs and support multiple monitors. Theoretically it should even be possible to work split screen. For example, to make a four-head (a multiseat for four users), it will require four monitors, four keyboards, four mice (remember that most motherboards have only one PS-2 or serial ports) and two dual or four single output video cards (again, remember that most motherboards have only one PCIe or AGP slot, so PCI cards will be needed).

[edit] How to do it

There are already a lot of different ways to make multiterminals, and new ways are constantly being developed. There is not a "best version", but some versions are better than others.

[edit] Using Linux

The following text is copied and (badly) translated from this article.

On the Unix operating systems, like Linux, the interaction with the user is made by the X Window System. This system is based on the client-server architecture, where the client sends drawing requests to the server and receives from these events the input (keyboard and mouse). The X servers have a recources concept, like an input device or a window, that are given to his clients. These resources are associated to a Display, that belongs to a user. Therefore, an Unix based multiterminal must provide a Display for each user.

The Xorg, the most recent X server implementation, doesn't have support for multiple displays. Following the personal computer model, it is estimated that only one user uses the machine at a time. Its input layer is implemented over the kernel standard input, the virtual terminals (VT). They recive this name because they simulate the old mainframes' input method. The VT is fully implemented using software, but simulates the tty, a device that was connected trough serial ports. The Linux kernel supports multiple terminals, but only one can recive keyboard events at a time. If more than one keyboard is connected to the computer, the keyboard events will be sent to the active VT. That hinders the execution of two or more X servers, because only one can be active on a determined moment, even if they use distinct video hardware.

To avoid these problems, a lot of different solutions have been made. They are listed here, in chronologic order.

Multiterminal with Ruby (applying a kernel patch)
Multiterminal with evdev (a protocol)
Multiterminal with faketty (a kernel module)
Multiterminal with Xnest (a nested multiterminal)
Multiterminal with Xephyr (a nested multiterminal)
Multiterminal with Userful Desktop Multiplier (a virtualized Xserver)
Multiterminal with framebuffer Driver in the kernel ( a kernel module)

The most used are faketty and Xephyr. The Xephyr solution is independent of hardware, while faketty only works with a more restrict set of video-cards (ex.: NVIDIA).

[edit] Case studies

[edit] Paraná Digital project

One of multiterminal's successful cases is happening at Paraná Digital project. It is creating multiterminal laboratories on 2000 public schools of the state of Paraná (Brazil). More than 1.5 million users will benefit from the 40,000 terminals when the project is finished. The laboratories have four-head multiterminals running Debian. The cost of all the hardware is 50% less than the normal price, and there is absolutelly no cost with software. This project developer is C3SL (Center for Scientific Computing and Free Software).