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# ItC Week 12 - Operating System

###### tags: `Intro_to_Comp`

- ## What is OS
- Goals
- Execute user programs and make solving user problems easier
- Make the computer system convenient to use
- Use the computer hardware in an efficient manner
- A resouce allocator
- Manage which resource can be used by which program
- A control program

- ## Startup
- "bootstrap program" is loaded at powerup or reboot
- Usually stored in ROM or EPROM
- aka firmware
- Initialize system in all aspects
- Loads OS kernel and transfer control to it

- ## Intertupt
- Function
- An interrupt transfers control to the interrupt service routine
- Through the "Interrupt vector", which contains the addresses of all service routines
- Interrupt architecture must save the address of the interrupted instuction
- A "trap" or "exception" si a software-generated interrupt caused by either an erro ror a user request
- An OS support such things is "interrupt driven".
- Interrupt handling
- OS preserves CPU state by storing registers and program counter
- Determines which type of interrupt has occerred
- Vectored interrupt system
- Polling
- poll each possible I/O device, check for requests

- ## Cache
- Use some faster storage to store often-accessed data
- Replacement policy
- FIFO
- MRU
- LRU

- ## System Architecture
- Multiprocessors
- pros
- increase throughput
- economy
- increase reliability
- types
- asymmetric
- symmetric
- Types
- Asymmetric Multiprocessing
- each processor is assigned with a specific task
- SYmmetric Multiprocessing
- each processor performs all tasks

- ## Clustered Systems
- Multiple systems working together
- Share storage via a storage-area network (SAN)
- high-availability bc is can survive some failure
- Asymmetric clustering
- one machine in hot-standby mode
- Symmetric clustering
- multiple nodes running apps and monitoring each other
- Some have distributed lock manager to avoid conflicting operations

- ## OS Structure
- Multiprogramming (Batch System)
- job scheduling
- switch other job when waiting (like I/O)
- Timesharing (Multitasking)
- CPU scheduling
- memory swapping
- virtual memory

- ## OS Operations
- Interrupt
- hardware
- software
- software error
- system request
- infinite loop....
- Dual-mode
- allow OS protects and other system components
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