Systems Software Flashcards
Operating System
Collection of programs/software that MANAGE HARDWARE and PROVIDE AN INTERFACE FOR USER AND APPLICATION SOFTWARE.
EXAMPLES: Windows, Linux.
What does the OS handle
-Memory Management
-Interrupt Handling
-Processor scheduling
-File management
-Providing user interface
-I/O management
-Security
Different types of OS
-Distributed
-Embedded
-Multi tasking
-Multi user
-Real time
Different types of memory management
Paging: Memory split into EQUAL SIZED CHUNKS called pages. Memory allocation is NON-CONTIGUOUS.
Segmentation: Memory split into LOGICAL SIZED CHUNKS called segments. Each segment represents one part of a program (i.e subroutine). CONTIGUOUS.
Virtual Memory: Section of Hard Drive used as RAM for programs not being used. Moved to VM via paging.
Problems with Virtual Memory
Can cause Disk Thrashing - Computer freezes due to frequent swapping of pages between hard disk and memory.
MORE TIME SPENT TRANSFERRING PAGES THEN RUNNING PROGRAMS.
How does the OS handle interrupts
-Stores interrupts in a priority queue in an interrupt register.
-Uses interrupt service routine to ensure interrupts handled fairly by checking interrupt register at end of FDE cycle.
-If an interrupt exists with Higher priority than interrupt being handled, contents pushed to a stack.
- Processor responds to interrupt by loading ISR to RAM, flag is set (signalling beginning of ISR)
-Rest of queue is checked for higher priority processes. If so, process repeats.
-Otherwise, contents of stack loaded back into registers and FDE cycle continues.
Different forms of processor scheduling
(PRE EMPTIVE)
-Round robin
-Shortest Remaining time
-Multi-level feedback queues
(NON PRE EMPTIVE)
-First come first served
-Shortest Job first
Round robin
- Each job allocated a time slice to execute a process.
-Once all jobs have used a slice, each job that still needs to be completed is allocated another slice.
-Continues until all jobs are executed.
Shortest Remaining Time and its risk
-Queue is ordered based on time left for completion, with least time being completed first.
Issue: Risk of processor starvation for larger jobs if small jobs keep being added.
Multi level feedback queue
Makes use of multiple queues, each ordered based on different priority. Difficult to implement.
First come first served
Jobs processed in chronological order, does not allocate time based on priority.
Shortest Job first and Issues
Queue ordered according to time required to complete job.
Requires processor to know how long each job will take which is not known always.
Risk of processor starvation for larger jobs.
BIOS
Basic Input Output System - Runs when computer is turned on.
PC points to location of BIOS upon startup.
Responsibilities include:
- Running the Power On Self Test to ensure all hardware components are functioning
- Checking if CPU clock memory and processor are operating.
- Testing for external memory devices connected to computer.
- Loads OS into RAM AFTER ALL CHECKS ARE COMPLETE
Device Drivers
Computer Programs provided by OS to allow it to interact with hardware.
- Driver communicates request made by user to produce relevant output.
- They are specific to a computers architecture and the OS installed on the device.
Virtual Machines
Theoretical computers that is a software implementation of a computer.
Provides environment with the translator for intermediate code to run.
Intermediate code
Lies between machine and object code, used to translate source code into machine code.
Independent of processor architecture and can be used across different machines.
Uses of Virtual machines
Create a development environment for programmers to test programs on different OS.
- Saves time and money of having to purchase multiple devices. Intermediate code can also be slower than low level code designed for VM.
Protection from malware as the VM is affected instead of actual device.
Running incompatible software (programs specific of different OS can be run within VM saving time and money).
Systems software
Low level software responsible for running computer system smoothly, interacting with hardware and providing platform for applications software to run.
Applications software
Software designed to be used for one specific task, requires system software.
Examples: word processors, web browsers, spreadsheets, desktop publishing.
Utilities
Key pieces of system software that ensure consistently high performance of OS. Each utility has a specific function linked to maintenance of OS
Examples:
Compression
Disk defragmentation
Antivirus
Automatic updates
Backup
Types of utility
Compression: Used on files of large size. Reducing the size of a file.
Disk defragmentation: Rearranges contents of hardware so files can be accessed faster, improving performance.
Antivirus: Detects potential threats to the user, receiving threat and alerting user.
Automatic Updates: Ensure OS is kept up to date, updates occur when computer restarts. Tackle bugs and security flaws ensuring system is less vulnerable to malware.
Backup: Automatically creates routine copies of specific files selected by the user. Frequency of backup chosen by user. Files can be recovered in case of power failure or malicious attack.
Source code
Object code before it has been compiled. Either open or closed.
Open source
Can be used by anyone without a license, distributed with source code.
ADV: Can be modified and improved by anyone. Technical support from online community can be modified and sold on.
DISADV: Support online may be insufficient/incorrect. No user manuals. Lower security as not developed in a controlled environment.
Closed Source
Requires user to hold a license to use it. Users cannot access source code as company owns copyright license.
ADV: Thorough, regular, well tested updates. Company providing software provides expert support and user manuals. High levels of security.
DISADV: License restricts how many people can use it. Users cannot modify and improve software themselves.
