OS interface, scheduling routines

Benefits of user interface to users + examples

• Interface hides complexity of computer hardware/OS from user

• Provides appropriate access systems for users with differing needs

• Complex commands involving memory locations are avoided

• Clicking on an icon instead of writing code

• Using icons for navigation

Multitasking definition

• Allows computers to seem to carry out more than one process at a time

How multitasking is implemented in an operating system

• Processor time and resources are shared between tasks

• Scheduling is used to decide on the processes to be carried out to ensure multi-tasking operated efficiently

• One task of a higher priority can interrupt another task that is currently running

Multitasking + how it benefits process management

• Running multiple processes concurrently

  • Benefits process management by allowing more tasks to be completed than would be the case if they had to run one task after another

Function of shortest remaining time scheduling routine + benefit

• Processes are queued as they arrive

• Processes with the shortest burst time (CPU time needed to execute) are executed first

• Pre-emptive schedule function (when shorter burst time arrives, replaces longer process)

• **Shortest job first is non-premptive (continue until complete)

• Starvation may occur - Scheduler will continue to choose shorter processes over longer processes if added, meaning they are pushed back indefinitely

• Processes with a short burst time are processed very quickly

• Wait time minimised

• Higher throughput of processes (many short tasks in little time)

Reasons why scheduling is necessary in process management

• Process scheduling is required to ensure 

  • Enables multitasking

  • Minimizes CPU idle time

  • Ensure no starvation (fair access to resources)

  • Ensures processes completed in order of priority 

Function of round robin scheduling routine + benefit

• Processes queued as they arrive

• Pre-emptive scheduling routine

• Each process has an equal time slice

• When time slice ends, status of process is saved

• Moves onto next process to be executed within time slice

• Reduces average response time by limiting each process to a fixed amount of time

• No issued with starvation of resources

Types of scheduling routines

• Round robin

• Shortest job first

• First come first served

• Shortest remaining time

Two ways in which complexities of computer hardware are hidden from the user

• Provision of user interface

  • Icons and menus used to control devices

• Use of device drivers

  • Easier to control peripherals such as printers within the operating system rather than in the separate device itself 

• Device mapping

  • Different devices(physical and virtual) are easy to identify on the network, check their status or use

• User interacts with Application layer (TCP/IP protocol suite)

  • Leaving the lower layers and their complexities hidden from the user

How operating system ensures that multi-tasking operates efficiently

• Operating system monitors the state of each task

• Using scheduling to ensure hardware resources are used efficiently 

  • And making sure that tasks do not clash

First come first served

• No complex logic is used, each request is received and executed one by one

• Executed in order of arrival

• No starvation