What are system calls? Explain how a user application requests memory allocation from the operating system using system calls. Illustrate the transition between user mode and kernel mode with a neat diagram.

A software company has recently expanded its operations from one office to five geographically distributed development centres. The management wants employees to access shared computing resources without knowing the physical location of the servers.

Process Allocation Maximum Requirement

P1 1 0 1 3 2 2

P2 2 1 0 4 2 2

P3 0 1 2 2 2 3

P4 1 1 1 3 3 2

A manufacturing company uses four processes (P1–P4) competing for three resources (A, B and C). The resource allocation is shown below.

ompare a Distributed Operating System and a Network Operating System with respect to:

Resource sharing

Transparency

Scalability

Fault tolerance

Suggest the most suitable operating system model for this organization with proper justification.