Operating System
A set of procedures that enable a group of users to share a computer installation or the computing resources efficiently.
Components of an Operating System
• Process Management
• Memory Management
• I/O System Management
• File Management
• Protection/Security System
Components of a Unix System
• Kernel
• System Libraries
• System Utilities
The UNIX kernel has the ability to load and unload arbitrary sections of kernel code on demand. These loadable kernel modules run in privileged kernel mode, and as a consequence have full access to all the hardware capabilities of the machine on which they run.
Kernel Modules
Module Management -- allows modules to be loaded into memory and talk to the rest of the kernel..
Driver Registration – allows modules to tell the rest of the kernel that a new driver has become available.
Conflict-Resolution – allows different device drivers to reserve hardware resources and to protect those
resources from accidental use by another driver.
The features that account for the popularity of UNIX !
• Time-sharing multi-user operating system
• Multitasking
• Portability with minor changes
• Protection at file and directory level
• Powerful user interface and command structure
• Support to various communications protocols
UNIX File System
Organization of Files in UNIX is in a hierarchical structure of subdirectories
UNIX file is a simply a sequence of characters (not wholly true). It places no restrictions on the structure of the file.
A file contains exactly those bytes that you put into it, be it a source program, executable code or anything else. It neither contains its own size nor its attributes, including the end-of-file mark.
Components of an Operating System
• Process Management
• Memory Management
• I/O System Management
• File Management
• Protection/Security System
Components of a Unix System
• Kernel
• System Libraries
• System Utilities
The UNIX kernel has the ability to load and unload arbitrary sections of kernel code on demand. These loadable kernel modules run in privileged kernel mode, and as a consequence have full access to all the hardware capabilities of the machine on which they run.
Kernel Modules
Module Management -- allows modules to be loaded into memory and talk to the rest of the kernel..
Driver Registration – allows modules to tell the rest of the kernel that a new driver has become available.
Conflict-Resolution – allows different device drivers to reserve hardware resources and to protect those
resources from accidental use by another driver.
The features that account for the popularity of UNIX !
• Time-sharing multi-user operating system
• Multitasking
• Portability with minor changes
• Protection at file and directory level
• Powerful user interface and command structure
• Support to various communications protocols
UNIX File System
Organization of Files in UNIX is in a hierarchical structure of subdirectories
UNIX file is a simply a sequence of characters (not wholly true). It places no restrictions on the structure of the file.
A file contains exactly those bytes that you put into it, be it a source program, executable code or anything else. It neither contains its own size nor its attributes, including the end-of-file mark.
UNIX can be viewed as two major layers
Kernel
Shell
Shell - Acts as an interface between the user and the kernel. The shell is a Command Line Interpreter (CLI).
It interprets the commands the user types in and arranges for them to be carried out. The commands are themselves programs: when they terminate, the shell gives the user another prompt (% on our systems).
The Sell can be uses as a keyboard interface to the operating system, a vehicle for writing scripts for your own personal use and as a programming language to develop new commands for others.
The most popular shell are – Bourne, Korn, C and Bourne Again Shells.
The Shell typically performs the following activities in each cycle of its execution:
• It issues the $ prompt, and waits for you to enter a command.
• After a command has been entered, the shell scans the command line for some special characters, and then rebuilds the command line after processing is complete
• The command is then passed on to the kernel for execution, and the shell waits for its completion
• The $ prompt appears, and the shell waits for you to enter the next command
Kernel
Shell
Shell - Acts as an interface between the user and the kernel. The shell is a Command Line Interpreter (CLI).
It interprets the commands the user types in and arranges for them to be carried out. The commands are themselves programs: when they terminate, the shell gives the user another prompt (% on our systems).
The Sell can be uses as a keyboard interface to the operating system, a vehicle for writing scripts for your own personal use and as a programming language to develop new commands for others.
The most popular shell are – Bourne, Korn, C and Bourne Again Shells.
The Shell typically performs the following activities in each cycle of its execution:
• It issues the $ prompt, and waits for you to enter a command.
• After a command has been entered, the shell scans the command line for some special characters, and then rebuilds the command line after processing is complete
• The command is then passed on to the kernel for execution, and the shell waits for its completion
• The $ prompt appears, and the shell waits for you to enter the next command
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