CDAC Operating System Basics | What is an OS ?
What is an OS?
- An Os is a system software (i.e. collection of system programs) which acts as an interface between user and hardware.
- An OS also acts as an interface between programs and hardware as an OS allocates resources like CPU time, main memory access, io devices access to all running programs, it is also called as "resource allocator".
- As an OS manages available resources among all running programs, it is also called as "resource manager".
- As an OS not only controls an execution of all running programs it also controls hardware devices which are connected to the computer system, it is also called as "control program".
- An OS is a s/w comes in a CD/DVD contains:
- OS = Kernel + Utility Programs + Application Programs
- > Kernel - it is a core part/program of an OS which runs continuously into the main memory does basic minimal functionalities of an OS.
- >Utility Programs: e.g. disk manager
- >Application Programs: e.g. MS Office
- Installation - it is a process to store/to copy os s/w programs from CD/DVD into the computer machine i.e. into the hard disk drive.
- Booting - to load kernel from hard disk drive into the main memory.
- "bootable device" - if any storage device contains one special program called as "bootstrap program" in its first sector i.e. in a boot sector then such as device is called as bootable device, and if boot sector is empty then that device is referred as "non-bootable".
- There are two steps of booting:
- 1. machine boot:
- step 1 - when we switched on the power supply current gets passed first to the mother board, and one micro-program named as "BIOS" exists in the ROM memory which is exists onto the motherboard gets invoked first.
- step 2 - first step of BIOS is POST(Power On Self Test), under POST it checks whether all peripherals are connected properly or not and their working status.
- step 3 - after POST, "bootstrap loader" program gets executed, this program searches for available bootable devices and selects any one at a time.
- 2. System boot:
- step 4 -- upon selection of bootable device as HDD, "bootloader program" gets invoked which exists in it, which displays list of name of an operating systems installed onto the machine, so user need to select any one out of it.
- step 5 -- upon selection of any operating system bootstrap program of that OS/parition gets invoked, bootstrap program locates the kernel and load it into the main memory.
- Basic minimal functionalities:
- 1. Process Management
- 2. Memory Management
- 3. Hardware Abstraction
- 4. CPU Scheduling
- 5. File Management
- Extra utility functionalities:
- 6. Protection and Security
- 7. Networking
- 8. User Interfacing:
- There are two types of interfaces given by an OS for user
- 1. CUI: Command User Interface/CLI -
- - user can interacts with an OS by means entering commands through CLI program
- i.e. command line interpreter program
- e.g. Linux -> "shell"
- windows -> "cmd.exe"
- ms dos -> "command.com"
- 2. GUI: Graphical User Interface:
- - user can interacts with an OS by means of making an events like right click, left click, double click, clicks etc.
- e.g. windows -> "explorer.exe"
- Linux -> "GNOME"/"KDE"
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