Computer Organization and Architecture: Chapter 3 - A Top-Level View of Computer Function and Interconnection

What is software?

A sequence of codes or instructions Part of the hardware interprets each instruction and generates control signals Provide a new sequence of codes for each new program instead of rewriting the hardware

Instruction address calculation (IAC)

Determine the address of the next instruction to be executed. Usually, this involves adding a fixed number to the address of the previous instruction.

I/O address register (I/OAR)

specifies a particular I/O device

What are the three key concepts of Von Neumann Architecture?

• Data and instructions are stored in a single read-write memory. • The contents of this memory are addressable by location, without regard to the type of data contained there. • Execution occurs in a sequential fashion (unless explicitly modified) from one instruction to the next.

Op code for Load AC from Memory

0001 1

Op code for Store AC to Memory

0010 2

Op code for Add to AC from Memory

0101 5

Accumlator

A variable used to store a number that is incremented by a changing amount.

Control

An instruction may specify that the sequence of execution be altered.

Instruction Operation Decoding (IOD)

Analyze instruction to determine type of operation to be performed and operand(s) to be used.

What is the fetch cycle?

At the beginning of each instruction cycle the processor fetches an instruction from memory The program counter (PC) holds the address of the instruction to be fetched next The processor increments the PC after each instruction fetch so that it will fetch the next instruction in sequence The fetched instruction is loaded into the instruction register (IR) The processor interprets the instruction and performs the required action

Program Counter (PC)

Contains the address of the next instruction to be executed.

Memory Buffer Register (MBR)

Contains the data to be written into memory or receives the data read from memory

Instruction Register (IR)

Contains the instruction currently being executed

Processor-memory

Data may be transferred from processor to memory or from memory to processor.

Processor-I/O

Data may be transferred to or from a peripheral device by transferring between the processor and an I/O module.

Operand Fetch (OF)

Fetch the operand from memory or read it in from I/O.

Operand address calculation (oac)

If the operation involves reference to an operand in memory or available via I/O, then determine the address of the operand.

Components of the I/O pertaining to software:

Input module Contains the basic components for accepting data and instructions and convertig them into an internal form of signals usable by the system. Output module Means reporting results

Basic Instruction Cycle contains what two steps?

Instruction cycle: Single instruction Fetch cycle Execute

Components of the CPU pertaining to software:

Instruction interpreter Module of general_purpose arithmetic and logic fucntions

Partial list of op codes

Load AC from Memory Store AC to Memory Add to AC from Memory

Data Operation (DO)

Perform the operation indicated in the instruction.

Internal CPU registers

Program Counter Instruction Register Accumulator

Instruction Fetch (IF)

Read instruction from its memory location into the processor.

Memory Address Register (MAR)

Specifies the address in memory for the next read or write

How should control signals be supplied?

The entire program is actually a sequence of steps. At each step, some arithmetic or logical operation is performed on some data. For each step, a new set of control signals is needed.

Data processing

The processor my perform some arithmetic or logic operation on data.

What does instruction processing consist of?

The processor reads (fetches) instructions from memory one at a time and executes each instruction. Program execution consists of repeating the process of instruction fetch and instruction execution. The instruction execution may involve several operations and depends on the nature of the instruction.

What is a hardwired program?

The result of the process of connecting the various components in the desired configuration

What does general purpose hardware do?

The system accepts data and control signals and produces results. Thus, instead of rewiring the hardware for each new program, the programmer merely needs to supply a new set of control signals.

I/O buffer register (I/OBR)

Used for the exchange of data between an I/O module and the CPU

Operand Store (OS)

Write the result into memory or out to I/O.