Operating Systems and System Software Flashcards
What is the purpose of a stack when handling interrupts?
Allows the processor to…
- Retrieve previous values for the original program
- Load them back into the processor registers
- Carry on executing the original program from where it left off
What happens to the values of the registers when an interrupt is received?
They are pushed onto a memory stack in a stack frame
Where are multi-user operating systems used?
In environments requiring collaboration and resource sharing among multiple users
What is the main advantage of multi-tasking systems?
Enhances user productivity and system efficiency by allowing the simultaneous execution of processes
Where are multi-tasking systems used?
Desktop environments - to run multiple applications simultaneously
Servers - to manage several user requests or services (hosting, database management, file sharing)
What is a multi-tasking operating system?
An OS which allows multiple tasks or processes to run concurrently
What is the BIOS?
A program responsible for loading the operating system when the computer first turns on
What is a boot loader?
A program used to load the OS kernel into memory
What happens once the OS has been loaded?
It takes over from ROM and boots up the rest of the system
What does the BIOS do first when turned on?
Checks all the hardware it needs is connected and working using POST (power on self test)
Clears anything that may still be in the registers of the CPU
Loads the address of the first instruction into the PC
State 5 roles of the OS
File management
Memory management
Peripheral management
Providing a user interface
Utility software
Processor scheduling
Interrupt management
Security
State the 5 scheduling algorithms
Round robin
First come first served Shortest remaining
Multi-level feedback queue
Shortest job first
Describe the round robin scheduling algorithm
Each process is given an equal time slice
If a process is not complete within the time it joins the back of the queue
Higher priority tasks can interrupt the process
Describe the first come first served scheduling algorithm
Processes are dealt with in the order they come
No system of priorities
Describe the shortest remaining time scheduling algorithm
Jobs with the shortest remaining estimated time are executed until finish or until a job with a shorter remaining time interrupts the process
Describe the multi-level feedback queue scheduling algorithm
Sorts jobs into categories depending on their priority level
Describe the shortest job first scheduling algorithm
Jobs with the shortest execution time are processed first
State all the pre-emptive scheduling algorithms
Round robin
Shortest remaining time
Multi-level feedback queue
State all the non pre-emptive scheduling algorithms
First come first served Shortest job first
What is a preemptive scheduling algorithm?
An algorithm where an executing process can be interrupted when a higher priority process comes
What is a non-preemptive scheduling algorithm?
An algorithm where an executing process cannot be interrupted. The high priority must wait until the end of execution.
State an advantage and disadvantage of preemptive algorithms
Advantage
- more reliable
- average response time is improved
- flexible - critical processes can be attended to
Disadvantage
- low priority processes have to wait if multiple high-priority processes arrive at the same time
State an advantage and disadvantage of non-preemptive algorithms
Advantage
- minimal scheduling burden
- very easy procedure
- high throughput rate
Disadvantage
- rigid: critical processes have to wait for the CPU to finish processing
- bugs can cause computer to freeze up
Explain how round robin works
- OS sets an interrupting clock
- clock generate interrupts at specific times
State the main advantage of round robin
Guarantees a reasonable response time to all users of the system
State an advantage and disadvantage of shortest job first and shortest remaining time
Advantage
- reduces number of waiting jobs
- reduces number of small jobs waiting behind big jobs
Disadvantage
- requires knowledge of how long a job will take
What is a multi-user operating system?
An OS which allows many users to access the system and its resources at the same time
Give an example of where a multi-user OS is used
In a computing lab where many students login to a computer and access the same resources without interference
What is a distributed operating system?
An OS which allows many computers to work together to carry out a single task
Give an example of where a distributed OS may be used
Processing an order from an online shop
What is a real-time operating system?
An OS designed to carry out action within a fixed and assured amount of time
Give an example of where a real-time OS may be used
A heart monitor in a hospital
What is an embedded operating system?
An OS designed to run inside single-use systems rather than general-purpose computers
Give an example of where an embedded OS may be used
Washing machine
Describe the process of a computer booting up
- POST is run
- checks components are available
- clears CPU registers
- loads address of first instruction
- boot loader program carries out checks on hardware
- checks for BIOS
- combines with basic BIOS on ROM (boot file) and sends to RAM
- loads OS from hard disk
- OS takes control
State and explain 2 advantages of the BIOS
- non-volatile : allows system to boot up with correct configurations every time
- can be easily updated or rewritten : enables firmware updates
- more reliable than traditional methods : reduces risk of data loss
- compact + small physical footprint : suitable for limited space on motherboard
What is a device driver?
Software that tells the operating system how to communicate with a peripheral device
What is the purpose of a device driver?
To facilitate communication between the OS and hardware devices
What does a device driver do?
Translates operating system instructions into a series of instructions that a specific piece of hardware will understand
State an advantage of device drivers
- simplifies programming
- enhances portability
- ensures compatibility between various hardware components : don’t have to worry about hardware specific programming
- provides mechanisms for error detection and handling
What is a virtual machine?
A program that has the same functionality as a physical computer
What can a virtual machine be used for?
To support a large number of virtual servers spread over a small number of physical servers
- if one stops the others can pick up the load
What is intermediate code?
Programming language translated into half-code (byte-code) then translated by a virtual machine on the target device into specific machine code
State the advantage of intermediate code
makes code highly portable between devices
Explain why interrupts are used
- to signal to the CPU that a process needs attention
- allows OS to allocate adequate processor time
What is paging?
The physical division of memory in to fixed equal sized sections called pages
What is segmentation?
The logical division of memory into variable-sized section called segementswhich depend on the program structure
