3.1 Common System Components
Main Memory Management
I/O System Management
A process is a program in execution. A process needs certain resources, including CPU time, memory,
files, and I/O devices, to accomplish its task.
The operating system is responsible for the following activities in connection with process management.
1. Process creation and deletion.
2. Process suspension and resumption.
3. Provision of mechanisms for:
4. Process synchronization
5. Process communication
1. Memory is a large array of words or bytes, each with its own address. It is a repository of quickly
accessible data shared by the CPU and I/O devices.
2. 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:
1. Keep track of which parts of memory are currently being used and by whom.
2. Decide which processes to load when memory space becomes available.
3. Allocate and de allocate memory space as needed.
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:
1. File creation and deletion.
2. Directory creation and deletion.
3. Support of primitives for manipulating files and directories.
4. Mapping files onto secondary storage.
5. File backup on stable (nonvolatile) storage media.
I/O System Management
The I/O system consists of:
1. A buffer-caching system
2. A general device-driver interface
3. Drivers for specific hardware devices
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:
1. Free space management
2. Storage allocation
3. Disk scheduling
Networking (Distributed Systems)
A distributed system is a collection processors that do not share memory or a clock. Each processor has its own local memory. The processors in the system are connected through a communication network.
Communication takes place using a protocol.
A distributed system provides user access to various system resources.
Access to a shared resource allows:
1. Computation speed-up
2. Increased data availability
3. Enhanced reliability
Protection refers to a mechanism for controlling access by programs, processes, or users to both system and user resources.
The protection mechanism must:
1. distinguish between authorized and unauthorized usage.
2. specify the controls to be imposed.
3. Provide a means of enforcement.
Many commands are given to the operating system by control statements which deal with:
1. Process creation and management
2. I/O handling
3. Secondary-storage management
4. Main-memory management
5. File-system access
The program that reads and interprets control statements is called variously:
1. Command-line interpreter
2. Shell (in UNIX)
Its function is to get and execute the next command statement.