OPERATING SYSTEMS PROCESS MANAGEMENT

• Program execution – system capability to load a program into memory and to run it.
• I/O operations – since user programs cannot execute I/O operations directly, the operating system must provide some means to perform I/O.
• File-system manipulation – program capability to read, write, create, and delete files.
• Communications – exchange of information between processes executing either on the same computer or on different systems tied together by a network. Implemented via shared memory or message passing.
• Error detection – ensure correct computing by detecting errors in the CPU and memory hardware, in I/O devices, or in user programs.
  

MAIN MEMORY MANAGEMENT

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

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.

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

• Many commands are given to the operating system by control statements which deal with:
  * process creation and management
  * F/O handling
  * secondary-storage management
  * main-memory management
  * file-system access
  * protection
  * networking
  
  
• 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.