Computers 2 Flashcards
What is the
operating system?
(OS)
The most important software on a computer that:
- enables hardware to communicate effectively with the software
- provides an interface for users to interact with the computer
- organises and keeps track of files stored on a computer’s secondary storage
- is responsible for access control
- allocates programs their share of the CPU, main memory and peripherals and keeps track of their progress
When the computer starts up, the operating system is loaded and performs a number of key functions.
How does the operating system organise and keep track of files stored on a computer’s secondary storage?
Using a hierarchical tree structure.
The top node of the tree is the root directory. Nodes lower down are either, directories, sub-directories or files.
Every file in the system has a unique path so that it can be easily located. This also allows the filename to be used more than once.
When there’s a new file to be stored, the operating system splits it up into smaller pieces and stores each piece in an empty sector on the hard drive. It keeps a record of the start location and sequence number of each piece so that it can retrieve and rename the file when it is required.
The operating system provides a number of functions for users to manage their files and directories, such as save, open, copy, duplicate, reassemble and delete.
Where are programs stored on a computer?
on a hard drive or some other form of secondary storage
they are loaded into the computer’s main memory in order to be executed
What is a
process?
a program that is loaded into main memory and is being executed
some processes are visible to the user as application software, but others run unnoticed in the background
What are some different strategies that an OS uses to ensure that each process gets a share of CPU time?
- first in, first out
- shortest job first
- round robin
Describe the scheduling algorithm
first in, first out.
Processes queue in the order in which they arrive. The process at the head of the queue gets to use the CPU until it is finished or is held up waiting for another resource.
(like a printer)
Describe the scheduling algorithm
shortest job first.
the process which is closest to finishing goes next
Describe the scheduling algorithm
round robin.
Each process is assigned a time slice. Processes wait their turn in a queue. The process at the head of the queue goes next. At the end of its time slice, if it isn’t finished, it goes to the back of the queue and the next process is taken from the front of the queue.
some processes have higher priority than others and get more time slices
