The Great Symbian

SYSTEM COMPONENT

Operating Systems Process Management

A process is a program in execution. A process needs certain resources: CPU time, memory (address space), files, and I/O devices, to accomplish its task.

The operating system is responsible for the following activities in connection with process management.
-->Process creation and deletion.
-->Process suspension and resumption.
-->Provision of mechanisms for:
-->Process synchronization
-->Process communication

Main Memory Management

Memory is a large array of words or bytes, each with its own address. It is a repository of instructions and data shared by the CPU and I/O devices. Main memory is a volatile storage device. It loses its contents in the case of system failure.

The operating system is responsible for the following activities in connections with memory management:

-->Decide which processes to load when memory space becomes available.
-->Allocate and deallocate memory space as needed. Keep track of which parts of memory are currently being used and by whom.

File Management

A file is a collection of related information defined by its creator. Commonly, files represent programs (both source and object forms) and data.

The operating system is responsible for the following activities in connections with file management:

-->File creation and deletion.
-->Directory creation and deletion.
-->Support of primitives for manipulating files and directories.
-->Mapping files onto secondary storage.
-->File backup on stable (nonvolatile) storage media.

Before mounting,
-->Files on floppy are inaccessible

After mounting floppy on b,
-->Ffiles on floppy are part of file hierarchy

I/O System Management

The I/O system consists of:
-->A buffer-caching system
-->A general device-driver interface
-->Drivers for specific hardware devices

Secondary Storage Management

Since main memory (primary storage) is volatile and too small to accommodate all data and programs permanently, the computer system must provide secondary storage to back up main memory.

Most modern computer systems use disks as the principle on-line storage medium, for both programs and data.

The operating system is responsible for the following activities in connection with disk management:

-->Free space management
-->Storage allocation
-->Disk scheduling

Protection System

Protection refers to a mechanism for controlling access by programs, processes, or users to both system and user resources.

The protection mechanism must:

-->Distinguish between authorized and unauthorized usage.
-->Specify the controls to be imposed.
-->Provide a means of enforcement.

Command-Interpreter System

Command-Interpreter reads commands from the user or from a file of commandsand executes them, usually by turning them into one or more systemcalls. It is usually not part of the kernel since the command interpreteris subject to changes.

The program that reads and interprets control statements is called variously:
-->command-line interpreter
-->shell (in UNIX)

Its function is to get and execute the next command statement