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.
