Networking
A distributed system is a collection of processors that do not share memory, peripheral devices, or a
clock. Processor has its own local memory and clock, and the processors communicate another through
various communication lines. The Processors in a distributed system vary in size and function.
The Processors in the system are connected through a communication network, which can be configured
in a number of different ways. The network may be fully or partially connected.
Protection System
Computer System has multiple users and allows the concurrent execution of multiple processes, the
various processes must be protected from one another’s activities. For that purpose, mechanisms
ensure that the files, memory segments, CPU, and other resources can be operated on by only those
processes that have gained proper authorization from the operating system. Device Control registers
are not accessible to users, the integrity of the various peripheral devices is protected. Protection is
any mechanism controlling the access of programs, processes, or users to the resources defined by
a computer system main for specification of the controls to be imposed and means for enforcement.
Protection can improve reliability by detecting latent errors at the interfaces between component
subsystems. Early detection of interface errors can often prevent contamination. A protection-oriented
system provides a mean to distinguish between authorized and unauthorized usage.
Command-Interpreter System
The most important program for an operating system is the command interpreter, which is the interface
between the user and the operating system. Ms-Dos and UNIX, treat the command interpreter as a
special program that is running when a job is initiated, or when a user first logs on. Many Commands
are given in a batch system be control statements. When a new job is started in a batch system, or when
user logs on to a time-shared system, a program that reads and interprets control statements is executed
automatically. This program is sometimes called the control-card interpreter or the command-line
interpreter, often known as the shell. User-friendly command interpreter make the system more reliable.