Chapter 4.1 (B) Interupts Flashcards
What is multi-tasking
A function that allows a computer to process more than one task/process at a time
What does the computer have to monitory in order to perform multi tasking
risk?
» the time that resources have been allocated to a process. There is a time limit
» Priority of a process (the risk here is that a low priority process could be starved of resources).
What do multiple account allow a user to do
» customise their screen layout and other settings
» manage separate folders and files themselves
What is a user-account
Allows an individual to use a computer; the user needs a user name and password to enter the his/her area
What is booting up/bootstrap loader
a small program that is used to load part of the operating system into RAM
What does the BIOS tell the computer and what does it do
Where the storage device that holds the operating system can be found
It then loads the part of the operating system that is needed and executes it.
What is firmware
a program that provides low level control for devices.
Where is the BOIS stored
what is it
EEPROM - a flash memory chip, which means its contents remain even when the computer is powered down. However, it also means the BIOS can be rewritten, updated or even deleted by a user.
Where are the BIOS settings stored
full form
how is it powered
what does this mean
what happens once restarted
CMOS chip - Complementary Metal Oxide Semi-conductor)
CMOS is powered up at all times via a rechargeable battery on the motherboard.
Therefore, the BIOS settings would be reset if the battery was removed or disconnected for some reason.
Once the CMOS is re-started, it will access the same BIOS program from EEPROM, but the settings will now be the default factory settings.
What is an interrupt
a signal sent from a device or software to a microprocessor requesting its attention
Causes of an interrupt
» a timing signal
» an input/output process (for example, a disk drive or printer requiring more data)
» a hardware fault (for example, a paper jam in the printer)
» user interaction (cntrl + c in the middle of a program executing)
» software errors that cause a problem (trying to divide by 0)
What happens after an interrupt is sent
how does the microprocessor decide what to do
microprocessor either carries on with what it was doing or stops to service the device or program that caused the interrupt.
Computer establishes a interrupt priority
What is interrupt priority
Interrupts are given a priority so that the microprocessor knows which one needs to be serviced first and which interrupts are to be dealt with quickly
What does it mean to service an interrupt
what happens if interrupt is not serviced
Action needs to be taken by the processor depending on what caused the interrupt.
Until interrupt is serviced it cannot be removed and allow the process to continue
How does a microprocessor serivce an interrupt
The status of the current task being run first needs to be saved.
The contents of the Program Counter (PC) and other registers are saved.
ISR is executed by loading the start address into the Program Counter (PC).
Once the interrupt has been fully serviced, the status of the interrupted task is reinstated - (the contents of all the saved registers are then retrieved)
