A multi-user system or multi-user system is an operating system that offers the possibility of providing and delimiting work environments for different users.
The idea of having several users work with one computer dates back to the early days of mainframe computers , when many IT users had to share few resources. In the past, the computers were mainly used in universities and a few large companies. Used in their operation terminals , which consist only of a keyboard and a screen were passed and connected to the main computer.
To amortize the high acquisition costs, unused computing time was rented to other interested parties, for example to companies for carrying out their accounting or for product development. It could happen that the data processing of a competitor ran on the same computer. It was therefore necessary to shield the databases of different users from one another.
The preparation of the data carriers and the starting of these " jobs " were carried out by the operating staff so that the administrators could carry out their actual tasks. In order to avoid operating errors, this staff was only given limited access rights .
For the development of the first multi-user systems, see time sharing (IT) .
When the first microcomputers were available, semiconductor memories were very expensive, so they were accordingly scarce. In order to save memory space, the operating systems available for microcomputers have been reduced to the bare minimum. Which at the time widespread DOS is therefore not a multi-user system, as well as on MS-DOS -building Windows 3.x - and -9x systems from Microsoft.
The multi-user capability of an operating system is achieved through a bundle of individual measures. This includes, for example, the management of private working directories and personal preferences for individual users. On multi-user systems, users also expect a concept for the management of access rights to stored data and other system resources.
The term multiuser does not necessarily refer to simultaneous work. There were also computers on which different users could work one after the other in their own working environment, but not at the same time. If multitasking was planned, a user could at least have several tasks carried out at the same time. When different users have their own working environments available at the same time, this is called multisession .
Systems that are not only multi-user capable, but also multi-tasking, usually require a memory protection concept. Current computer systems mostly work with virtual address spaces in the main memory, which are configured with hardware support from an MMU (as a separate module on the main board or directly in the processor ) for a specific process or user.
Multi-user systems in networks
Some multi-user systems also allow registration via computer networks , e.g. B. the Internet . So many different users around the world can connect to the computer via the Internet, log in and work on the same machine at the same time. This solution came about primarily for cost reasons, because individual computers used to be very expensive. Today this approach is rarely found. The console (command prompt, Unix shell ) of Linux or Unix systems is still called the "terminal" today.
The rights system of a multi-user system primarily protects its users from spying attempts by other users and data loss through unintentional deletion of files. The biggest advantage, however, is the safeguarding of system integrity when used without administration rights. A malicious program can only spread as far as the user's write permissions are sufficient. System -wide distribution, compromising the kernel or basic system services and thereby automatic activation at system start-up can only be achieved by using special attack vectors such as B. Setuid or security gaps in applications possible.
- Apple MacOS from 1992
- Microsoft Windows NT (depending on edition, version and license, only limited use.)
Multi-user systems outside of operating systems
In a broader sense, multi-user systems can not only be operating systems , but all application systems that can work for more than one user. To do this, they too (in addition to the operating system) must be able to process the activities of several users separately from one another and offer certain technical requirements (e.g. protection against simultaneous changes to the same data).
Opposite: single user system.
- Applications for graphics or text editing are i. d. R. Single User Systems; Only one creator can work on the result file (at the same time).
- A ticket ordering system is a multi-user system if orders can be processed by several users at the same time.
- Aids for project management can be single-user systems (e.g. to create a schedule). If several users at the same time z. B. can report back their work results, there are multi-user systems .