CHAPTER : SYSTEM SOFTWARE Flashcards
1
Q
Purpose of an Operating System
A
- OS provides an environment on which application software can be executed
- allows software to communicate with the hardware
- required to manage the computer system
- manages memory usage
- provides filing system
2
Q
Key Manageemnt Tasks of the OS
A
- provides means of communication (UI) between the user and the computer
- manages the physical resources like processors, HDD,input/output etc.
- provides a platform where the applications can run
- controls access, allows to making passwords to restrict and control access rights
- provides utility software like diskformatter, automatic updates etc. that carry out tasks that are necessary for the computer to run
- file management: allows user files to be managed using folders
3
Q
What is a benefit of the User Interface
A
- it hides the complexities of the computer’s OS from the user
- complex commands involving memory locations are avoided
eg: clicking on icons directly as oppose to writing the code to open a software
4
Q
Process Control Block
A
complex data structure containing all relevant data to execute process
5
Q
Process State: READY
A
- new process has arrived at the memory, PCB created capable of using processor but has to wait
6
Q
Process State: RUNNING
A
- process currently usin the Processor (has CPU access)
7
Q
Process State: Blocked/Suspended
A
cannot progress to use the processor as:
- doesn’t have enough resources to execute the instruction
- waiting from some signal from another process
8
Q
Running state –> Ready state
A
- when time slice of the current running process expires and another process of higher priority os on the ready queue, running process is pre-empted
9
Q
Multitasking
A
- managing the execution of many programs that appear to be running simultaneously
10
Q
Why does the OS needs to schedule
A
- it allows for multitasking
- ensures there is fair usage of the processors, peripherals and memory
- ensure the higher priority tasks are executed sooner
- ensure all processors have a chance to finish the process they are on
11
Q
Low - Level Scheduling : Pre-Emptive
A
- will stop the process that would have otherwise continued to execute
12
Q
Low - Level Scheduling : First Come First Served
A
- non preemptive
- FIFO
13
Q
Low - Level Scheduling : Round Robin
A
- allocates time slice to each process
- preemptive and can be FIFO
- doesn’t prioritse
14
Q
Low - Level Scheduling : Priority Based
A
- most complex
- priority reevaluated on queue change
- priority calculation requires computation
15
Q
Low - Level Scheduling : Shortest Job First
Low - Level Scheduling : Shortest Remaining Time
A
- process with the shortest run time
- shortest estimate run time
16
Q
What is a Kernel
A
- acts as a low level interrupt handler
17
Q
Tasks of Kernel
A
- load/unload applicaiton from memory
- schedule tasks for efficient run on CPU
- memory management
- file storage to and from secondary storage
- file management
- data security
18
Q
Interrupt
A
- signal seeking CPU attention and causes OS Kernel to invoke ISR
19
Q
Interrupt Handling
A
- transferring control to another routine when service is required
20
Q
Memory Allocation: Segmentation
A
- application divided into fixed size elements when program compiled
- loader calculates the number of segments the program requires
- programmers code a code to minimise the segments required
21
Q
Memory Allocation: Paging
How paging is used to manage virtual memory
A
- the memory is split into frames
- the virtual memory is divided into blocks of the same size that are fixed
- and the page table is set up to translate between the logical and physical addresses
- swap pages into memory with new pages from disk when required
- keep track of all free frames
22
Q
Page:
A
virtual memory divided into blocks of fixed sizeP
23
Q
Page Frame
A
main memory divided into page frames (same size as pages)
24
Q
Page Table
A
shows mapping of page to page frames
translates the logical addresses to physical addresses
25
Virtual Memory
- uses secondary storage to simulate additional main memory
26
What is Virtual Memory
- it is the secondary storage that is used to extend the RAM
- so that the CPU can access more memory than available
- only data in use needs to be in RAM
- therefore data is swapped between the disk and the RAM
27
Why OS uses Virtual Memory
- VM is used when RAM is running low
- When computer is running many processes at once
- VM allows for efficient use of the RAM
28
Benefits of Virtual Memory
- not the entire program needs to be in the RAM
- large programs can run with/without the physical memory space being available
29
Disk Thrashing
- a disadvantage of using virtual memory
- it happens when the pages in RAM and virtual memory are interdependent
- pages are required back in RAM as soon as they are moved into the VM
- no useful processing gets done as the same pages are being swaped back and forth
30
Lexical Analysis
- it converts sequence of characters in a sequence of tokens
- creates keyword and symbol table
- removes white spaces and comments
- identifies source code errors like invalid variables and incorrectly spelt keywords
31
Syntax Analysis
- it double checks code for grammar (syntax errors)
- makes use of tree data structures (parse tree)
- produces an error report
32
Code Generation
- intermediare code genweration
- produces object code (after compilation of source code)
33
Code Optimisation
- code edited to improve efficiency
- to decrease the time taken to execute by reducing instructions and occupy less memory space
34
How contents of keyword and symbol table used to translate source code program
- keywords looked up and represented by tokens
- identifiers looked up and then converted to location
- the used to create sequence of tokens
35
Explain how interpreter executes without full translation
- Interpreter examines source code one statement at a time
- Checks if there are any errors
- If not it executes the line of code
- Else it produces an error report and the interpreter stops
- interpretation is repeated for each iteration
36
Reverse Polish Notation
- provides an unambigious way of representing expression without brackets
37
Main Steps of RPN
- works from left to right
- if element is a number it is pushed onto the stack
- if element operator, the first two numbers are popped and calucation is performed
- and answer is pushed back on stack
- ends after last item in expression is done
