Basics of Operating System

In this article, I will share some basic terms of Operating System in simple words.

Basics of Operating System

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Interrupts:

• Interrupts are the signal sent by the I/O device to the processor.
• When any I/O device is attached to the processor, it sends a signal to the processor to gain attention. Processor stops its current activity and pays attention to the device.

There are three types of interrupts:

Hardware Interrupts:

• They are the signal sent by the hardware device to the processor. 
• The signal is sent to an interrupt line.
• When an interrupt is signaled, the processor executes a routine (interrupt handler), to deal with the device.
• Each device is assigned an Interrupt number. This number is used by the processor to identify the device.
• Hardware interrupts are generated when a device has performed its action, such as printing a document, sending files, etc.

Software Interrupts

They are generated by the program when they request System Call. A system call is performed by the OS.

System Call:

When an application needs a hardware operation, it requests OS to perform this operation. This request is called System Call. It is generated by currently running processes.

Traps:

They are generated by the CPU itself. When an error occurred, Interrupts are signaled to inform OS. Then, OS takes possible action to resolve the error.

Bios:

• Bios stands for Basic Input Output System.
• It is a firmware located on the motherboard.
• It is non-volatile (permanent), and retains its information when a computer is powered off.
• It performs three tasks:

1. When a computer is switched on, it performs POST (Power On Self Test). It checks the initialization of all hardware components.
2. ‎It loads the operating system. After the POST, it locates the bootloader and reads hard drive boot sector to continue the process of loading OS.
3. ‎It allows basic setup of computer settings. You need to enter into Bios setup

CMOS:

• It stands for Complementary Metal Oxide Semiconductor.
• It is a memory chip, uses CMOS battery for power.
• It stores current date & time of the system and boot sequence. It stores bios settings as well.
• It stores small data, like 256 bytes.
• It tells the computer, the hardware device where OS boot files are present. It also tells the sequence in which the devices should be checked.
• You can change the sequence.

Kernel:

• It is a computer program, core of the operating system.
• It is the first program loaded after boot-loader.
• It handles the rest of startup and I/O request from software. It translates the requests into data processing instructions for the CPU.

OS modes:

There are two types of OS modes i.e Kernel and User mode.

The application software is not allowed to access hardware directly. The OS protects the access of hardware using these modes.

Kernel Mode:

• It is also known as Privileged or Supervisor mode.
• It has public virtual address space.
• The instructions in this mode can access hardware directly, without any restrictions.
• If a crash occurs in this mode, it is catastrophic. The whole OS will be crashed.

User Mode:

• It is less privileged
• The access to hardware is restricted
• Each process has private virtual address space, visible to only themselves
• If a crash occurs, the process will get crashed.
• The program switched from user mode to kernel mode.

Batch OS

• This OS was used in mainframes and older computer systems
• The process executes sequentially in order.
• Each process takes some time in execution. The time taken is the sum of CPU time and I/O time.
• The process which loads firsts will be executed first. 
• The scheduling algorithm follows the sequential order for process execution.
• We don't get results from different processes simultaneously.

Multi-programming:

• It improves the efficiency of the CPU.
• The processes execute simultaneously.
• Each process with less CPU time is executed sequentially.
• When the process has completed it's CPU time, the process starts executing other processes.
• The processor executes some part of the program (CPU time), then other parts of another and so on.
• It keeps the CPU busy.

Conclusion

If there is anything I could not clearly explain, just let me know pals. I tried to be as honest in sharing this valuable information as I could. I have shared almost everything I have learned so far.
Do let me know how much did this help you. Peace and blessings buddies. :)