| To bridge the user and the computer hardware, since the user cannot communicate with the hardware directly | What is the purpose of an operating system? |
| - Control Hardware
- Manage software (loading into RAM)
- Provide security (username and password)
- Provide user interface
- Processor scheduling | Name 5 functions of an operating system |
| - Kernel
- Drivers
- User Interface
- System Utilities | Name the 4 main parts of an OS |
| Paging is fixed size (4Kb) segments, segmentation is varying length segments | What's the difference between paging and segmentation and how big is a page? |
| - Pages are fixed size | What is one difference between pages and segments? |
| The allocation of segments or sections of memory to allow a process to run | What is memory segmentation? |
| Suspends the execution of the current process, puts the values of the Program Counter and the other registers onto the stack temporarily, completes the task, then loads the values back into the registers from the stack and continues as before | What happens when an interrupt occurs? |
| Efficiently and fairly allocating CPU time to different tasks to allow for multi-tasking. Usually smaller parts of multiple tasks are executed in succession to give the appearance of carrying out several tasks simultaneously | What is processor scheduling? |
| . | What are the types of scheduling algorithms? |
| Each process is given a limited amount of CPU time (time slice). If the process isn't completed before it's time expires, the despatcher gives the CPU the next process | How does Round Robin scheduling work? |
| To compensate for the difference in speed between the peripheral and the CPU | what is the point of a buffer (in the context of peripheral management) |
| The memory manager determines the least used page and copies it into virtual memory. The free area is re-numbered by the memory manager and marked as free for use | (paging) What happens if RAM is full but more pages are needed? |
| Quickly loading and unloading things from RAM | What causes disk thrashing? |
| When memory locations get 'locked up' because the data isn't properly flushed so the memory manager thinks it's still in use | What is a memory leak? |
| When a stack gets too full and runs out of free memory to use | What is stack overflow? |
| At the end of each fetch-decode-execute cycle | When does the CPU check for interrupts? |
| When the CPU regularly checks if an event or peripheral needs attention | What is polling? |
| When all registers are copied to the stack before executing an interrupt | What is context switching? |
| Stack overflow because each paused instruction is put in the stack until it is resumed so eventually the stack can overflow | What is a risk of too many interrupts interrupting other interrupts? |
| - Doesn't take into account how important a process is
- Doesn't consider that some processes are long and some are short | What are 2 disadvantages of round robin scheduling? |
| Each one is allowed to complete before moving on | What is first come first served scheduling? |
| - Doesn't account for processing time
- Doesn't account for priority | What are 2 disadvantages of first come first served scheduling? |
| Maximum number of jobs completed quickly but long jobs may never complete if shorter jobs keep interrupting | What is one good thing and one bad thing about shortest job first scheduling? |
| Shortest Time Remaining | Name the scheduling algorithm which fixes shortest job first's problem |
| Multi level feedback queue | What scheduling technique takes priority into account? |
| Multi-tasking OS | What is this type of OS called? - Windows, Linux, MacOS |
| Allocates each workstation time | How do multi-user OS' allow multiple workstations to access the mainframe? |
| Multiple computers all being controlled by one OS and sharing a task (spreading the workload) | What is a distributed OS? |
| - It must respond very quickly to any inputs or sensors
- It must be able to deal with many inputs simultaneously
- It must have "failsafe" mechanisms to detect and take appropriate action if a hardware component fails
- It must incorporate redundancy - if one component fails, it needs to automatically switch to backup hardware
- Used on planes and factory production lines | What are the 4 required features of a real-time OS and what are 2 examples of somewhere a realtime OS would be used? |
| - ATM
- Washing
- Car | Name 3 devices with embedded OS |
| The low-level real-time operating system in charge of radio and other hardware has system vulnerabilities | What is a problem with smartphones having 2 operating systems? |
| Boot up the computer - test the hardware and load the OS | What is the purpose of BIOS? |
| Basic Input Output System | What does BIOS stand for? |
| Non-volatile flash memory on the motherboard | Where is BIOS usually stored? |
| Running more than one OS on a computer | What is a use of a virtual machine? |
| Provides a software interface to a particular hardware device | What's the point of a driver? |
| Systems Software and Application Software | Software can be grouped into two categories, what are they? |
| Software needed to run the computer's hardware and application programs - this includes operating system, utility programs etc. | What is systems software? |
