#Operating-System

Software

# Topic covered
* Systems software
* Application software
* Operating System(OS)
* Types of OS
* Multithreading vs Multitasking 

Components of OS

1. Kernel
   • A kernel is that part of the operating system which interacts directly with the hardware and performs the most crucial tasks.
   • Heart of OS/Core component
   • Very first part of OS to load on start-up.
2. User space
   • Where application software runs, apps don’t have privileged access to the underlying hardware. It interacts with kernel.
   • App: GUI, CLI

32-Bit vs 64-Bit OS

• A 32-bit OS has 32-bit registers, and it can access 2^32 unique memory addresses.
  • i.e., 4GB of physical memory.
• A 64-bit OS has 64-bit registers, and it can access 2^64 unique memory addresses.
  • i.e., 17,179,869,184 GB of physical memory.
• 32-bit CPU architecture can process 32 bits of data & information.
• 64-bit CPU architecture can process 64 bits of data & information.

CPU Scheduling in Operating Systems

• Short-term schedular
• Move processes from: Ready Queue (Ready state)--> Running state
• CPU scheduling can be of two types
  • Non-Preemptive scheduling
  • Preemptive scheduling

Concurrency

• Concurrency is the execution of the multiple instruction sequences at the same time.
• It happens in the operating system when there are several process threads running in parallel

Deadlock

• A situation where a set of processes are blocked because each process is holding a resource and waiting for another resource acquired by some other process.
• This block situation is called Deadlock(DL)
• DL is a bug present in the process/thread synchronization method
• In DL, processes never finish executing, and the system resources are tied up, preventing other jobs from starting.

Memory Management Techniques

Logical versus Physical Address Space

• Logical Address
  • An address generated by the CPU while a program is running
  • The logical address is basically the address of an instruction or data used by a process.
  • User can access logical address of the process.
  • User has indirect access to the physical address through logical address
  • Logical address does not exist physically. Hence, aka, Virtual address
  • The set of all logical addresses that are generated by any program is referred to as Logical Address Space
  • Range: 0 to max

Non-contiguous Allocation

• The non-contiguous memory allocation also reduces memory wastage caused by internal and external fragmentation.
• Paging and Segmentation are the two ways that allow a process’s physical address space to be non-contiguous.