Systems Software

Question 1

What is the interupt process?

Answer 1

• Interupt request
• Importance of interupt is decided
• Coressponnding Interupt Service Routine (ISR) is found
• ISR execution
• Interupt exit

Question 2

What happens if the interupt is more important than the current task?

Answer 2

• FDE cannot be stopped halfway so current FDE cycle is completed
• Contents of registers is temporarily saved to the data structure stack in memory
• Processor hands control to coressponding ISR which completes response
• Contents of registers is restored

Question 3

What is interupt prioritisation and nesting?

Answer 3

• Interupt prioristisation is the processors ability to switch to higher priority interupts
• Nesting is the processors ability to deal with interupts within interups
• Proper management of nesting allows the system to remain stable

Question 4

What is scheduling?

Answer 4

• Deciding which tasks to process, for how long and in which order is achieved through scheduling
• A CPU is responsible for processing tasks as fast as possible
• Different algorithms are used to prioritise different tasks in different ways

Question 5

What is round robin scheduling?

Answer 5

• Equally distributes processing time amongst all tasks
• All tasks put in a queue
• If the task hasn’t been completed by the end of its time quantam (allocated time) it is moved to the back of the queue

Question 6

What is multi-level feedback queue scheduling?

Answer 6

• Shorter and more critical tasks are processed first
• All tasks join the highest priority but trickle down to lower priorities if they exceed the time quantam

Question 7

Why is memory management necessary?

Answer 7

• When a user opens an application, its data is loaded from storage into active memory so that it can run smoothly
• Primary memory is a limited resource so must be carefuly managed to allow efficient multi-tasking

Question 8

What 3 techniques are used in memory management?

Answer 8

• Paging
• Segmentation
• Virtual memory

Question 9

What is paging and how does it work?

Answer 9

• Method of chunking memory into equal-size blocks
• These chunks are known as pages
• Pages will be taken away from applications not in use and allocated to active applications
• Paging can lead to internal fragmenation
• Internal fragmentation will lead to unused memory

Question 10

What is memory segmentation and how does it work?

Answer 10

• Chunking memory into blocks that correspond to different types of data needed by an application
• Segments are not all the same size and are sized depending on the allocated data
• Segmentation can lead to external fragmentation
• This is because once an application finishes, data is moved out and the space left will be of an uneven size

Question 11

What is virutal memory and how does it work?

Answer 11

• If a computer is running low on memory, it can use secondary storage as an “extension” to its primary memory
• Vram creates an illusion of a larger memory and enables applciations to continue multi-tasking
• Accessing data in vram is slower than primary memory

Question 12

What is a distributed OS?

Answer 12

• Tasks run on multiple different machines appearing as one unit
• Used for efficient task distribution

Question 13

What is an embedded OS?

Answer 13

• The system running inside a device that is not primarily a computer system

Question 14

What is the BIOS and boot sequence?

Answer 14

• The BIOS is the first system to run and tells the computer how to boot
• It completes the POST tests
• If no errors are encountered during the POST tests, the bootstrap sequence is run

Question 15

What is a device driver?

Answer 15

• A piece of software that enable communication between the operating system and specific hardware devices
• Allows the OS to control and interact with hardware devices

Question 16

What is a virtual machine?

Answer 16

• Virtual machines are entire operating systems running inside another operating system
• VM management software includes a hypervisor that monitors all activity happening inside the VM

Question 17

When are virtual machines used?

Answer 17

• Cross platform compatability: not all software is compatible to run on all operating system. You can use a virtual machine to emulate a different operating system
• Software testing: isolate test environments, leaves the host computer unaffected. Can test multiple operating systems on one computer for greater compatability

Question 18

Consequences of using virtual machines

Answer 18

• VMs share the same hardware as the host computer; over-use of VMs can exhaust the host computer

Question 19

Different types of operating systems

Answer 19

• Embedded OS: designed for a specific task, running within a device that is not specifically a computer system
• Distributed OS: tasks are run on multiple machines appearing as a single unit
• Real time OS: designed for immediate data processing and responses
• Multi-user OS: supports multiple users accessing computer resources concurrently