ARCHITECTURE OF COMPUTER HARDWARE, THE ARCHITECTURE OF COMPUTER HARDWARE, SYSTEMS SOFTWARE, AND NETWORKING, AN INFORMATION TECHNOLOGY APPROACH, 5TH EDITION

Arithmetic/login unit (ALU), Control Unit (CU), and memory

Arithmetic/login unit (ALU), Control Unit (CU), and memory

the computer unit is made up conceptually of three major components:

Central Processing Unit (CPU)

The ALU and CU together are known as the ___________________________.

I/O interface

corresponds in function roughly to the input and output baskets

arithmetic/logic unit

the component of the CPU where data is held temporarily and where calculations take place.

control unit (CU)

controls and interprets the execution of instructions. It does so by following a sequence of actions that correspond to the fetch--execute instruction cycle. Most of these actions are retrievals of instructions from memory followed by movements of data or addresses from one part of the CPU to another.

program counter (PC), sometimes called an Instruction Pointer (IP)

The control unit determines the particular instruction to be executed by reading the contents of a ______________, sometimes called an ________________, which is part of the control unit.

program counter

Like the Little Man's location counter, the ______________ contains the address of the current instruction or the next instruction to be executed.

sequence of instructions

Normally, instructions are executed sequentially. The _________________ is modified by executing instructions that change the contents of the program counter.

memory management unit

A ____________________ within the control unit supervises the fetching of instructions and data from memory.

bus interface unit

In some CPUs, these two functions ( I/O interface and the memory management unit) are combined into a single ______________________.

location counter

The program counter in the CPU obviously corresponds to the ________________________ in the Little Man Computer, and the control unit itself corresponds to the Little Man.

memory

__________ corresponds directly to the mailboxes in the LMC.

register

a single, permanent storage location within the CPU used for a particular, defined purpose. It is used to hold a binary value temporarily for storage, for manipulation, and/or for simple calculations.

Note:

each register is wired within the CPU to perform its specific role. Unlike memory, where every address is just like every other address, each register serves a particular purpose. The register's size, the way it is wired, and even the operations that take place in the register reflect the specific function that the register performs in the computer.

.
1 to 128 bits

Registers also differ form memory in that they are not addressed as a memory location would be, but instead are manipulated directly by the control unit during the execution of instructions. Registers may be as small as a single bit or as wide as several bytes, ranging usually from ______ to _________.

accumulator

In the CPU, the equivalent to the calculator is known as the ___________.

general-purpose registers

It is often necessary to move data to and from the accumulator to make room for other data. As a result, modern CPUs provide several accumulators; these are often known as __________________. Some vendors also refer to these as user-visible or program-visible registers.

register file

Groups of similar registers are also sometimes referred to collectively as a _____________.

register unit

General-purpose registers or accumulators are usually considered to be a part of the arithmetic/login unit, although some computer manufacturers prefer to consider them as a separate _________________.

program counter register (PC or IP)

hold the address of the current instruction being executed.

instruction register (IR)

holds the actual instruction being executed currently by the computer. In the Little Man Computer, this register was not used; the Little Man himself remembered the instruction he was executing. In a sense, his brain served the function of the instruction register.

memory address register (MAR)

holds the address of a memory location

memory data register (MDR), sometimes known as the memory buffer register

will hold a data value that is being stored to or retrieved from the memory location currently addressed by the memory address register.

1. Registers can be loaded with values from other locations, in particular from other registers or from memory locations. This operation destroys the previous value stored in the destination register, but the source register or memory location remains unchanged.
2. Data from another location can be added to or subtracted from the value previously stored in a register, leaving the sum or difference in the register.
3. Data in a register can be shifted or rotated right or left by one or more bits. This operation is important in the implementation of multiplication and division.
4. The value of data in a register can be tested for certain conditions, such as zero, positive, negative, or too large to fit in the register.

Most registers support four primary types of operations:

clearing a register and inverting the 0s and 1s (i.e. take the 1s complement of the value)

loading the value zero into a register

addition of the value of 1 to the value in a register

incrementing the register

flags

The control unit will also contain several 1-bit registers, sometimes known as _____, that are used to allow the computer to keep track of special conditions such as arithmetic carry and overflow, power failure, and internal computer error.

status registers

several flags are grouped into one or more ______________

cells

Real memory, like the mailboxes in the Little Man computer, consists of _____, each of which can hold a single value, and of which has a single address.

the memory address register and the memory data register

two registers, __________________________ and __________________________, act as an interface between the CPU and memory.

1 bit

Each cell in the memory unit holds ____ of data.

memory address register

holds the address in the memory that is to be "opened" for data. The MAR is connected to a decoder that interprets the address and activates a single address line into the memory.

2^n

if there are n bits of addressing, there will be ___ address lines.

1. an address line
2. read/write line
3. activation line

There are three lines that control the memory cell:

read/write line

The ___________ determines whether the data will be transferred from the cell to the MDR (read) or from the MDR to the cell (write).

one hundred

The number of possible memory locations in the Little Man Computer, ___________ locations, was established by the two-digit address space in each instruction.

M=2^k

For a memory address register of width k bits, the number of possible memory addresses is

the # of bits in the address field of the instruction set

establishes how many memory locations can be directly addressed from the instruction

addressing modes

The different ways of establishing memory addresses within an instruction

MAR

Ultimately, the width of the ___ determines the maximum amount of addressable memory in the computer.

1.physical space for the memory chips
2. time required to decode and access addresses in a large memory

In modern computers, the ultimate size of memory is more likely limited by ______ or _______, rather than by the capability of the CPU to address such a large memory.

size of the data word

The ________________ to be retrieved or stored in a single operation is determined by the size of the memory data register and by the width of the connection between memory and the CPU.

dynamic RAM

Today, the primary memory in most computer systems is ________________.

1. read-write capable or read-only
2.volatile or nonvolatile

Memory today is characterized by two predominant operational factors and by a number of technical considerations. Operationally, the most import memory characteristics are whether the memory is _____________ or ______________.

nonvolatile

___________ memory retains its values when power is removed. (magnetic core memory)

volatile

___________ memory loses its contents when power is removed. (RAM used for regular memory)

1.the speed of memory access
2.the total amount of memory that can be addressed
3. the data width
4. the power consumption and heat generation
5. the bit density (specified as the number of bits per square centimeter)
6. cost is an additional factor

Important technical considerations include:

1.less expensive
2.requires less electrical power
3.generates less heat
4.can be made smaller
5.more bits of storage in a single integrated circuit.

advantages of dynamic RAM:

requires extra electronic circuitry that "refreshes" memory periodically; otherwise the data fades away after a while and is lost.

Disadvantage of dynamic RAM

1.doesn't require refreshing
2.faster to access than dynamic RAM
3.useful in very-high-speed computers and for small amounts of high-speed memory

advantages of static RAM

lower in bit density and more expensive

disadvantages of static RAM

volatile

Both dynamic and static RAMS are volatile: their contents are lost when power is turned off.

cache memory

Most modern systems also provide a small amount of static RAM memory that is used for high-speed access

firmware

at least some of the program code used to start a computer must be present in a nonvolatile segment of primary memory (otherwise there would be no program in memory to execute when the computer is powered up!)

EFI or SEFI, for [Secure] Extensible Firmware Interface

the newer version replacing the BIOS, or Basic Input Output System in newer machines

flash memory

serves as an inexpensive form of nonvolatile secondary storage for portable computer storage, digital cameras, tablets, smartphones, and other electronic devices; however, with the exception of the memory used at system startup, it is generally considered unsuitable for primary memory because it is not possible to write to a single memory location.

fetch-execution instruction cycle

the basis for every capability of the computer.

first step in the instruction cycle

the instruction must be fetched from memory. (The address of the current instruction to be executed is identified by the value in the program counter register--transfer that value into the memory address register [MAR], so that the computer can retrieve the instruction located at that address.
PC-->MAR

step 2 instruction cycle

transfer that instruction to the instruction register.
MDR-->IR

MDR-->IR

The instruction register will hold the instruction through the rest of the instruction cycle. It is the particular instruction in the IR that will control the particular steps that make up the remainder of the cycle. These two steps comprise the fetch phase of the instruction cycle.

IR[address]-->MAR

read the address part of the LOAD instruction, walk over to the mailbox specified by that address, read the data, and copy it into the calculator.

MDR-->A

Step 4 of instruction cycle. The notation IR[address] is used to indicate that only the address part of the contents of the instruction register is to be transferred. This step prepares the memory module to read the actual data that will be copied into the accumulator.

PC + 1 --> PC

The CPU increments the program counter, and the cycle is complete and ready to begin the next instruction. Step 5 of the instruction cycle.

The STORE instruction

PC-->MAR
MDR-->IR
IR[address]-->MAR
A-->MDR
PC + 1 --> PC

The ADD instruction

PC-->MAR
MDR-->IR
IR[address]-->MAR
A + MDR --> A
PC + 1 --> PC

synergy

Individual components are designed to work together in such a way that overall performance is enhanced beyond the performance of each component.

1. series of one hundred mailboxes 00-99.
2. a calculator
3. two-digit hand counter (instruction location counter.
4. Little Man

physical layout of the Little Man computer

in basket and an out basket

Other than the reset button on the hand counter, the only interactions between the Little man Computer and the outside environment are through an __________________________________.

operation code, or op code for short

the instruction part of the three-digit code is also known as an ___________________.

*Memory holds both programs and data; this is known as the stored program concept. The stored program concept allows programs to be changed easily.
*Memory is addressed linearly; that is, there is a single sequential numeric address for each and every memory location.
*Memory is addressed by the location number without regard to the data contained within.

The major guidelines that define a von Neumann architecture include the following: