Question

In regards to Modern Operating Systems provide the definitions of the following terms: Timesharing system and Multiprogramming system

Answer 1

Multiprogramming:

• Multiprogrammingbecame possible when disks were introduced to the computing world. The concept of multiprogramming relies on the capability of a computer to store instructions (programs) for long-term use. The goal is to reduce CPU idle time by allowing new jobs to take over the CPU whenever the currently running job needed to wait (e.g. for user I/O).
• It was also at this point when operating systems received a new responsibility - decision making. Before multiprogramming was introduced, the role of the operating system was simple and straight-forward - load a program into memory and execute it via the CPU.
• With the advent of multiprogramming, operating systems now faced different mechanics for program execution as multiple jobs now needed to be loaded into memory at the same time and several options existed for allocating CPU time.
• Two types of scheduling were introduced to handle this decision-making - job scheduling and CPU scheduling. Job scheduling refers to the selection of jobs to load into memory. CPU scheduling refers to the selection of a job existing in memory to execute via the CPU. In a computer system, both these decisions are made by the operating system.

Time sharing system:

• A time sharing system or Multitasking system allows many users to share the computer resources simultaneously. In other words, time sharing refers to the allocation of computer resources in time slots to several programs simultaneously. For example a mainframe computer that has many users logged on to it. Each user uses the resources of the mainframe -i.e. memory, CPU etc. The users feel that they are exclusive user of the CPU, even though this is not possible with one CPU i.e. shared among different users.
• he time sharing systems were developed to provide an interactive use of the computer system. A time shared system uses CPU scheduling and multiprogramming to provide each user with a small portion of a time-shared computer. It allows many users to share the computer resources simultaneously. As the system switches rapidly from one user to the other, a short time slot is given to each user for their executions.
• The time sharing system provides the direct access to a large number of users where CPU time is divided among all the users on scheduled basis. The OS allocates a set of time to each user. When this time is expired, it passes control to the next user on the system. The time allowed is extremely small and the users are given the impression that they each have their own CPU and they are the sole owner of the CPU. This short period of time during that a user gets attention of the CPU; is known as a time slice or a quantum.
• The time-shared systems are more complex than the multi-programming systems. In time-shared systems multiple processes are managed simultaneously which requires an adequate management of main memory so that the processes can be swapped in or swapped out within a short time.

Advantages of Time-sharing operating systems:

• Provides the advantage of quick response.
• Avoids duplication of software.
• Reduces CPU idle time.

Disadvantages of Time-sharing operating systems:

• Problem of reliability.
• Question of security and integrity of user programs and data.
• Problem of data communication.