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1.2.1 (Interrupts (Types of Interrupts (Hardware -----------------------…
1.2.1
Interrupts
Interrupt - a signal sent by a device sent along the control bus to the CPU to indicate that user input it requires attention or that user input is required
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CPU knows where to pick up the previous task after dealing with the interrupt as stacks are used to store the address of the code being executed while the address of the interrupt code is being executed
For multiple interrupts the main code is put on the stack first and the interrupts are put onto the stack in order of ascending priority.. the highest priority interrupts is then operated upon
Types of Interrupts
Hardware ------------------------------------------------------------------- Power Button Pressed -------------------------------------------------- Memory Parity Error (corrupt memory) ------------------------------
Software ------------------------------------------------------------------- Illegal Instruction Encountered -------------------------------------- Arithmetic Overflow ------------------------------------------------------- New log-on Request------------------------------------------------------
Input/output ----------------------------------------------------------------Buffer Nearly Empty -----------------------------------------------------Signal the completion of a data transfer to/from a device--------
Scheduling
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Round Robin
Circular FIFO order Each thing has a certain amount of time before it is sent to the back of the queue
Types of OS
Multi-Tasking
An OS that can handle the running of an active program that is directly in use and multiple other programs that aren't actively in us but are open in the background.
Each program is given a small slice of processor time, giving the impression of them running simultaneously
Multi-User
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Distributed
Similar to a multi-user network in that it is accessed by multiple computers. It combines the processing power of all computers on the network, presenting them t the user as a single system, to focus on a specific task such as CGI rendering
Embedded
An OS that is designed to perform a single purpose such as a washing machine. It is designed to accept the inputs from buttons and knobs, then wash the clothes once the start button is pressed
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The need for the OS
OS Purpose
Manage Processor - Deiciding which process is executed next and handling interrupts to the currently executed proesses
Managing Memory - allocating and managing memory used by processes using paging and segmentation; managing virtual memory
Managing Peripherals - using device drivers to translate OS instruction into those understood by peripherals i.e. printers
Provides platform for software - provide framework for applications to run i.e. make opening and closing files easier.
The user can also interact with the OS to manage files and use utilities like file explorer and defrag
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Managing Security - servicing and denying requests to access the resources connected to the computer i.e. shared drives
Providing UI - users interact with apps through the UI, this can be GUI, Windows Icons menus and Pointer(WIMP), menu driven or command line
Device Drivers
A piece of software that tells the OS how it can communicate with the device i.e. a printer, different printer types will use different processes for printing, an inkjet uses jets of inks while a laser uses toners that are magnetised to a page and burned on with a laser
Virtual Machines
Any instance where software is used t take on the function of a machine, including executing intermediate code or running an OS within another, an example would be an emulator used to simulate the running of an Xbox on a PC
