MELJUN CORTES BASIC STRUCTURES OF COMPUTERS

Basic Structures of Computers

Computer Types Functional Units Basic Operational Concepts Number Representation and Arithmetic

Operations Character Representation Historical Perspective

*Property of STI I0022

Computer Types

• Modern computers can be divided roughly into four general categories:–Embedded Computers– used for a specific purpose rather than for general processing

tasks–Personal Computers – used for dedicated individual use such as general

computation, document preparation, computer-aided design, audiovisual entertainment, interpersonal communication, and Internet browsing


Computer Types

–Servers and Enterprise Systems – large computers shared by a potentially large number of users

who access them from some form of personal computer over a public or private network.

–Supercomputers and Grid Computers – offer the highest performance and are the most expensive

and physically the largest category of computers

• Cloud Computing • where personal computer users access widely distributed

computing and storage server resources for individual, independent, computing needs through the Internet


Functional Units

• Five Parts: input, memory, arithmetic and logic, output, and control units


Functional Units

• Input unit accepts coded information from human operators Memory is the location where the information received is stored • The processing steps are specified by a program that

is also stored in the memory. • Results are sent back to the outside world through

the output unit.


Functional Units

• Control unit coordinates all actions. • Interconnection network provides the means for the

functional units to exchange information and coordinate their actions.


Functional Units

• Information categories– Instructions• Machine instructions• Govern the transfer of information within a computer as well

as between the computer and its I/O devices • Specify the arithmetic and logic operations to be performed

–Data• Numbers and characters that are used as operands by the

instructions


Functional Units

• Input Unit–Accepts coded information –Most common input device is the keyboard. –Other kinds of input devices include touchpad, mouse, joystick,

and trackball. –Microphones can be used to capture audio input –Cameras can be used to capture video input. – Internet, can also provide input to a computer from other

computers and database servers.


Functional Units

• Memory Unit–Primary Memory or Main memory• Fast memory that operates at electronic speed• Consists of a large number of semiconductor storage cells

representing one bit of information.• Read or written in a fixed size called words.• Addresses – provides easy access to any word in a memory,

provides location of a word.• Instructions or data can be written


Functional Units

– RAM• Any location can be accessed in a short and fixed amount of

time– Memory access time• Required to access one word• Ranges from nanoseconds to about 100 nanoseconds


Functional Units

• Cache Memory–Smaller and faster RAM unit–Holds sections of program that are currently being executed–At program execution, cache is empty–During execution, instructions are fetched and placed in the

cache


Functional Units

• Secondary Storage–Primary memory is expensive and does not retain

information when power is turned OFF.–Less expensive and used for less frequently accessed

information–Longer access times–Magnetic disks, DVD and CD and flash memory devices


Functional Units

• Arithmetic and Logic Unit–Performs addition, subtraction, multiplication, division or

comparison of numbers–Operands are brought to the processor–Stored in high-speed storage elements known as registers


Functional Units

• Output Unit–Counterpart of the input unit–Send process results to the outside world

• Control Unit–Coordinates the operation of the other units– Is the nerve center that sends control signals to the other

units and senses their states–Generates timing signals that govern the transfers


Functional Units

• Summary of Computer Operation–The computer accepts information in the form of programs

and data through an input unit and stores it in the memory.– Information stored in the memory is fetched under program

control into an arithmetic and logic unit, where it is processed.–Processed information leaves the computer through an

output unit.–All activities in the computer are directed by the control

unit.


Basic Operation Concepts

• Activity is governed by instructions

Load R2, LOC–Reads the contents of a memory location (LOC) and loads them

to the processor register (R2)– LOC data are preserved and R2 data are overwritten

Add R4, R2, R3–R4 = R2 + R3–R4 data are overwritten with the addition result

Store R4, LOC– LOC data are overwritten



• Memory – processor interconnection



• Processor Registers– Instruction register – holds the current instruction that is executed

–Program counter – contains the memory address of the next instruction to be

fetched and executed–General Purpose Registers – can hold operands for processing and other variety of

functions


Number Representation

• IntegersB = bn-1…b1b0

V(B) = bn-1x 2n-1+…b1 x 21 + b0



• Floating-Point Numbers– -2.34 x 1056

– +0.002 x 10-4

– +987.02 x 109

–Can not be encoded in a 32-bit integer

• Floating point representation– -1sign x F x 2E

– F – fraction, E - exponent



• Floating-Point Numbers–Follows the IEEE 754 Floating Point Standard– -1sign x F x 2E-bias

–Bias = 127 (single precision) and 1023 (double precision)


Example 1


Example 2


Character Representation

• All information in the computer must be represented by 0s or 1s, including letters and other characters

• American Standard Code for Information Interchange (ASCII) was established in the 1960s.

• Assigns binary patterns for numbers 0 to 9, all letters of the English alphabet (uppercase and lowercase) and many control codes and punctuation marks

• Used by most computers so that information is shared among computers• Provides a standard for printing and displaying characters by output

devices• Uses a total of 7 bits to represent each code







http://www.asciitable.com/


Performance

• Performance is how quickly it can execute programs– Technology – use of VLSI to fabricate circuits for a processor on a single chip

– Switching between 0 and 1 states is determined by transistor size– Smaller transistors switch faster

• Parallelism– Instruction-level Parallelism– pipelining

–Multicore Processors – multiple processing units in a single chip–Multiprocessors – many processors in a computer system


Historical Perspective

• First Generation–Key concept of a stored program was introduced–Assembly language was used to prepare programs and was

translated to machine language for execution–Basic arithmetic operations were performed in a few

milliseconds–Uses vacuum tube technology to implement logic functions



• Second Generation–Uses transistors instead of vacuum tubes–Magnetic core memories and magnetic drum storage devices –High-level languages such as Fortran were developed–Compilers were also developed



• Third Generation–Ability to fabricate to many transistors on a single silicon chip

called integrated circuit (IC) technology– Enabled faster and less costly processors and memory elements to

be built.– IC replaced magnetic core memories– Introduction of microprogramming, parallelism and pipelining



• Fourth Generation– Implementation of complete processors and large sections

of the main memory of small computers on a single chip.–Very large scale integration (VLSI) technology–Microprocessor – complete processor fabricated on a single chip

–Field Programmable Gate Arrays (FPGA)– allowed system developers to design and implement

processor, memory and I/O circuits on a single chip