Chapter 1 Summary

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COMPUTER SYSTEM OVERVIEW

Describe the basic elements of a computer system and their interrelationship.

Processor (CPU): controls the operations and performs data processing functions

Memory: stores data and programs

I/O components: move data between computer and external environment

System bus: provides for communication among the above elements

Explain the steps taken by a processor to execute an instruction.

Fetch stage: loads the instruction that is located in the address that the PC points at to the IR.

Execute stage: interprets the instruction and performs the required action and then increments the PC.

It repeats these steps until it is instructed to halt or it halts for some other reason.

Understand the concept of interrupts and how and why a processor uses interrupts.

An interrupt is a signal that the computer uses to signal the processor of some event. This event can be an error in the program it is running e.g. divided by zero or an overflow, it can be a timer within the processor or it can be a hardware error; but most importantly it can be used as a tool for the processor to perform slow I/O operations. The processor can ask a I/O device to do a task and continue with other tasks before the device finishes and is later notified that the task has been finished and can than react to that. This way the processor can be better utilized because it doesn't have to wait for a much slower device to finish its job.

List and describe the levels of a typical computer memory hierarchy.

Inboard memory: Registers, Cache and Main memory.

Outboard storage: Magnetic disk, CD, DVD etc.

Off-line storage: Magnetic tape

Registers are at the top of the hierarchy. It is the fastest storage, but stores fewest bits and is the most expensive one per bit. It is the one that is most frequently accessed by the processor.

The once below in the hierarchy are less frequently accessed by the processor, are less expensive per bit, can store more bits and are slower.

Explain the basic characteristics of multiprocessor and multicore organizations.

Multiprocessor is when the computer has more than one processor that share the same main memory, operation system and all components. By having more than one processor the computer can run tasks in parallel, if that is possible, and therefor scales up the performance with every added processor.

Multicore is build with more than one processor (core) in one chip. Level 2 and sometimes level 3 cache memory is build into the chip as well and the cores often share level 3 cache. With this method the performance of the processor can be significantly increased because the distance to cache memory has been increased and utilization of all the cores can be exploited using parallelism.

Discuss the concept of locality and analyze the performance of a multilevel memory hierarchy.

Understand the operation of a stack and its use to support procedure call and

return.

CPU Program counter (PC) - holds the address of the

next instruction to be fetched.

Instruction register (IR) - contains a fetched instruction, i.e. bits that specify the action the processor is to take.

Memory address register (MAR) - specifies the address in memory for the next read or write.

Memory buffer register (MBR) - contains the data to be written into memory and receives the data read from memory.

Input/output address register (I/O AR) - specifies a

particular I/O device.

Input/output buffer register (I/O BR) - used for the exchange of

data between an I/O module and the processor.

Accumulator (AC) - temporary storage.

Key terms

address register

cache memory

cache slot

central processing unit

data register

direct memory access

hit ratio

input/output

instruction

instruction cycle

instruction register

interrupt

interrupt-driven I/O

I/O module

locality

main memory

multicore

multiprocessor

processor

program counter

programmed I/O

reentrant procedure

register

secondary memory

spatial locality

stack

system bus

temporal locality