Operating System Concepts

Study Notes

An operating system acts as an intermediary between a user and the computer hardware, executing user programs, making problem-solving easier, and using hardware efficiently.
The operating system's goals include:
- Executing user programs and making problem-solving easier
- Making the computer system convenient to use
- Using the computer hardware efficiently

A computer system can be divided into four components:
- Hardware: provides basic computing resources (CPU, memory, I/O devices)
- Operating System: controls and coordinates the use of hardware among various applications and users
- Application Programs: define the ways in which system resources are used to solve computing problems (word processors, compilers, web browsers, etc.)
- Users: people, machines, or other computers

An operating system is a resource allocator that:
- Manages all resources
- Decides between conflicting requests for efficient and fair resource use
An operating system is a control program that:
- Controls the execution of programs to prevent errors and improper use of the computer
There is no universally accepted definition of an operating system, but it can be approximated as "everything a vendor ships when you order an operating system."

Main memory is the only large storage media that the CPU can access directly, and is:
- Random access
- Typically volatile
Secondary storage is an extension of main memory that provides large non-volatile storage capacity
Hard disks are a type of secondary storage that:
- Use rigid metal or glass platters covered with magnetic recording material
- Are logically divided into tracks, which are subdivided into sectors
- Have a disk controller that determines the logical interaction between the device and the computer
Solid-state disks are a type of secondary storage that:
- Are faster than hard disks
- Are non-volatile
- Use various technologies

Storage systems are organized in a hierarchy based on:
- Speed
- Cost
- Volatility
Caching is a technique used to copy information into faster storage systems, such as main memory being used as a cache for secondary storage
Device drivers are used to manage I/O operations for each device controller

Caching is an important principle performed at many levels in a computer (in hardware, operating system, and software)
Information in use is copied from slower to faster storage temporarily
Faster storage (cache) is checked first to determine if information is there
Cache management is an important design problem

A process is a program in execution, and is a unit of work within the system
A process needs resources to accomplish its task, including:
- CPU
- Memory
- I/O
- Files
- Initialization data
Process termination requires the reclaim of any reusable resources
A single-threaded process has one program counter specifying the location of the next instruction to execute
A multi-threaded process has one program counter per thread