YEAR 1 CO1 WEEK 24 OS (MEMORY MANAGMENT) AND WEEK 25 (TYPES OF OS, SCHEDULING)
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What is an operating system?
Core software controls how a computer operates.
What are the purpose of operating systems?
• Provides a user interface • Managing hardware/peripherals • Memory management • Manages CPU/handles interrupts • Provides security • Provides a platform to run other systems/software • Provides utilities for system maintenance
What are the parts of the operating system?
• The Kernel (heart of operating system) • Device drivers • The user interface • System utilities
What is the kernel?
Kernal in different operating systems may be responsible for slightly different blend of tasks. Loading/unloading applications from memory. Memory management. File management. Data security.
How does the kernel work?
Designed for operating system
What is a File Allocation Table (FAT) and what does it do?
A map of where your files are stored on a hard disk • Stores pointers/addresses to the start of files • Stores file names, file sizes and access rights • It allows the OS to identify free space in memory
What is NTFS (New Technology File System)
New Tech File System which supports larger hard drives, file sizes and longer file names
What is a device driver ?
It’s a script / info that enables the operating system to control and interface with hardware
What is GUI
Graphical user interface is a friendly way for people to interact with computers
What is CLI
Command line interface Simpler cause it’s text base
What are the types of scheduling
Round robin First come first serve Shortest job first Shortest remaining time Multi level feedback queue
What is round robin?
Gives an equal amount of time being processed Probs it a time slot so if to much it get ignored until comes back round, don’t do priority Advantages simple to implement
What is First come first serve
What ever one comes first is dealt with first Disadvantage Other jobs have to wait for the first to be done No priority system
What is Short job first
Does the smallest first Minimise the advantages Long task could get left for ages
What is multilevel feedback queue
Takes Ito account priority and Priority’s can be adjusted Very complicated Not very efficient if jobs all same priority
What is Shortest remaining time
Quickest job left to complete finish first
Define A Logical Address
Addresses at which an item appears to reside, generated by CPU.
Define Physical Addresses
Actual physical location of the storage cell in memory.
What needs to happen for a executable application to be run.
To run a process it has to be loaded into main memory. To run more than one process all have to be in main memory at the same time. When executable application loaded into main memory it becomes a ‘process’ and requires memory to run.
Describe Segmentation.
OS sets aside memory for process to use. This is called segmentation. A way of portioning memory. Variable Sized based on contents. Are logical divisions which hold complete sections of programs.
Define Paging.
Second type of memory management which designed to handle virtual memory.
Define a Page.
A fixed sized physical division of memory. Each page is contiguous.
Describe Pagination.
When RAM full memory manager determines least used page. Page then copied into virtual memory. Free area renumbered by memory manager and marked as free to use. If page needed again swapped back into RAM. ONLY USED WHEN VIRTUAL MEMORY IN USE.
What is Disk Thrashing.
When Virtual Memory in heavy use. As more pages are swapped eventually more time is being spent swapping pages than processing data.c