Chapter 4 : Operating systems and computer architecture
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What are the 14 things that the operating system does?
• Human computer interface (HCI) • Multitasking • Multiprogramming • Batch Processing • Error handling • Loading and running of applications/software • Management of user accounts • File utilities (e.g. copy, save, sort, delete) • Processore mangement • Memory management • Real-time processing • Interrupt handling routines • Security (manages log on, passwords) • Input and Output control
a) What is an interrupt? b) And what does it do?
a. An interrupt is a signal sent from a device or from software to the processor to request the processors attention if it is an error or a high priority task. b. It will cause the processor to temporarily stop what it is doing and service the interrupt.
When can interrupts occur?
• When a disk drive is ready to receive more data. • When an error has occurred, such as a paper jam in a printer. • When the user has pressed a key to interrupt the current process - an example could be keys being pressed simultaneously, • When a software error has occurred - an example of this would be if an .exe file couldn’t be found to initiate the execution of a program.
State the order of the Fetch Execute Cycle
• Copy contents of PC to the MAR and initiate memory read • Instruction read from memory location is copied to MBR (MDR) • Increment the PC (go to the next instruction) • Copy the instruction from the MBR to the IR (CIR) • Decode instruction • Execute instruction • Repeat from step 1
What does MAR stand for? - And what is its purpose?
Memory Address Register - hold a data or instruction address
What does MDR stand for? - And what is its purpose?
Memory Data Register - temporarily holds the contents in the MAR so it can be copied to the CIR
What does ALU stand for? - And what is its purpose?
Arithmetic and Logic Unit - it does bit wise and mathematical and logic operation
What does PC stand for? - And what is its purpose?
Program Counter - Contains the address of the next instruction
What does CIR stand for? - And what is its purpose?
Current Instruction Register - holds the current instruction
What are the 3 types of buses?
• Address Bus • Data Bus • Control Bus
What does the Address Bus do?
Carries signals relating to addresses between the processor and the memory
What does the Data Bus do?
Sends data between the processor, the memory unit and the input/output devices
What does the Control Bus do?
Carries signals relating to the control and coordination of all activities within the computer (examples include: the read and write functions)
What signal direction does the Address Bus have?
Unidirectional (signals travel in one direction only)
What signal direction does the Data Bus have?
Bi-directional (data can travel in both directions)
What signal direction does the Control Bus have?
This is regarded as being both unidirectional and bi-directional due to the internal connections within the computer architecture
What is a buffer?
It is used in computers as a temporary memory area
Where are buffers used?
They can be used to temporarily store a video while the video is being watched
What does the control unit do?
It controls the operation of the memory, processor and input/output devices