3. Operating systems

Question 1

Functions of operating systems:

Answer 1

• Oversee (bevaka) the operation of a computer.
• Store and retrieve files.
• Schedule programs for execution.
• Coordinate the execution of programs.
  (OS är en grundläggande program)

Question 2

Execution of programs:

Answer 2

_Job - a program to be executed with its inputs and outputs.
_Batch processing - execution of a batch of jobs without any interaction of a user (originally operated by a computer operator)
_Interactive processing - support of interactive between programs and users during execution (originally via terminals)
_Real time processing - execution of tasks in accordance with deadlines in external real world environment. (The opposite of Batch processing)

Question 3

Multiple users and multiple programs:

Answer 3

_Multiprogramming - multiple programs can be executed “at the same time” (originally during batch processing) on a processor. It does not run programs at the “same time” it jumps from a program to the other and so multiple programs can run at the same time.
_Time-sharing - a computer provides services to multiple users “at the same time” (time slices) It does not run programs at the “same time” they share the processor’s time.
_Multitasking - multiple programs can be executed “at the same time” by a single user.
_More complexity with multiprocessor/multicore machines regarding utilization of increasing number of processors/cores.