User application programs do not directly communicate with hardware devicesinstead they communicate via the operating system which has the capability to give instructions to the hardware to perform specific tasks hence being the main/ only program that can enable the user access application programs. 

DefinitionIs a set of complex programs that work together to control user applications and also acts as a go-between, between the applications and the computer.

The OS consists of two parts namely: 

  • Shell

outer part of the operating system used to interact with the operating system. And, 

  • Kernel 

the core of the operating system used to manage and control computer resources such as main memory. It is also regarded as operation system

Just to outline a few of the operation system functions other than the above named are; 

Interrupt handling

this is a break from the normal sequential processing of instructions in a program, so the OS interrupts the C.P.U in its processing so as  the C.P.U can attend to another process before returning its attention to the interrupted process

Resource allocation 

each available resource in a computer is given a unique identification number known as  interrupt request (IRQ) which the OS uses to identify the resource being requested. 

Poor allocation of IRQ leads to deadlock (situation where a particular job holds a requested resource and fails to release it yet it is requesting for a resource held by the other job). 

Error handling

The OS monitors the state of the system and performs audit checks on users, hardware and software hence helping in easy error identification. 

Other functions include

  1. processor scheduling
  2. input/ output handling 
  3. communication control & management.

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