Topic 3.2 Computer Architecture

By: Victoria Dea

• Structure of the central processing unit (CPU)

• Bits and Bytes and their derivatives

• Word, register and address and their use in the storage of data and instructions

• Steps in the machine instruction cycle

• The characteristics of primary memory and volatile vs. non-volatile

• Secondary memory characteristics and sequential and direct address

• Function of a microprocessor

• Features, advantages and application of specific input and output devices and their media

• Recent development in computer system architecture (processor architecture, primary memory technologies and secondary memory devices).

Topic 3.2 Computer ArchitectureClick on a Topic

3.2.1 Structure of the CPU

• CPU- Central Processing Unit

• Arithmetic and Logic Unit (ALU)- Makes

logical comparisons and performs calculations

• Control Unit (CU)- decodes program instructions and sends control signals to other parts of the computer

• IAS- Immediate Access Storage– It is primary memory– Contains instruction and data

• CU and ALU form the microprocessor which contain various registers

Structure of the CPU

• Buses are a collection of wire and is most often an even number of bytes

• The IAS’s contain instructions and data which are transferred to the CU via buses.– Buses also transfer data between the primary memory

and the ALU

• Main types of buses are : address bus and data bus• Control bus is often in the computer design

– It tells the data bus if the data is moving from the primary storage to the ALU or vice versa.

A

B

C

D

What is ALU?

The Arithmetic Logic Unit

The Access Locking Unit

A shortened version of aluminum

The Address Locating Unit

Correct!

ALU stands for Arithmetic Logic Unit and it makes logical comparisons and performs

calculations.

3.2.2 Bits and Bytes

• Computers use the binary number system to operate

• Bits– Abbreviation: b

– shortened version of “Binary digit.”

– smallest unit of storage in memory

– almost always put together in groups of 8

• Bytes– Abbreviation: B

– 8 bits make 1 byte

Bits and Bytes

• Computers store bytes of data in larger units:– kB: kilobyte == 1024 bytes– MB: megabyte == 1024 kilobytes– GB: gigabyte == 1024 megabytes– TB: terabyte == 1024 gigabytes

• Note that computer storage is measured in units of 210 (1024)

D

How many bits are in a byte?

1024A

B

C

10

8

2

Correct!

Bits are put together in groups of 8 called bytes

3.2.3 Word, Register, and Address

• Word- the number of units of memory that a CPU typically handles at one time

• Register- a small amount of computer memory, typically holds one word of data

• Address- identified by a unique binary code– Memory has a sequence of addresses – However many bits the address has determines the

number of address locations the CPU can address

A

B

C

D

What is a register in a computer?

A component of the CU

A microchip that does calculations

A small amount of computer memory

A machine that stores money

Correct!

A register is a small amount of computer memory that typically holds one word of data

3.2.4 Machine Instruction Cycle

• Machine instruction cycle describes the main steps that occur in the execution of machine language instructions

• Also know as:– Fetch-Execute– Fetch-Execute-Decode– Fetch-Execute-Decode-Store

• The interrupt register is examined to see if the CPU needs any more processes before the next instruction cycle

D

What is the first step in the Machine Instruction Cycle?

Store results back in the IAS

A

B

C

Decode the instruction in the CIR

Fetch the next instruction from the IAS into the CIR

Execute the instruction

The Machine instruction cycle begins with Fetch.

Correct!

3.2.5 Characteristics of Primary Memory

• Primary memory (IAM) stores program instructions and data using binary.

• The CU deals with the instructions.• The ALU handles the calculations and comparisons with

the data. • Data and instructions are moved by buses.

• Two types of primary memory (aka Immediate

Access Storage):– RAM- Random Access Memory– ROM- Read Only Memory

Characteristics of Primary Memory

RAM

• Random Access Memory• Volatile• Loses whatever is stored

when the computer is shut off.

ROM

• Read Only Memory• Non-volatile• Used to store programs

permanently

• When software is not in RAM, they are stored on secondary memory, aka backing store, such as tapes and discs. • Peripherals are the collection of tapes or discs drives and input and output devices connected to the CPU.

Characteristics of Primary Memory

• Cache Memory:– When the processor has to look for the next instruction, it is most

often in the cache. – Internal cache memory is in modern processers– Very fast because of the short distance travelled– Typical size of the cache memory is a couple of megabytes.

• Virtual Memory:– Applications are too large to be stored in RAM or there is more

than one application running at a time. – This is handled by keeping sections of primary memory on high

speed secondary storage

What does RAM stand for?

Random Access MemoryA

B

D

C

Real Access Monitor

Really Amazing Memory

Recognizing Arrays Machine

RAM is Random Access Memory which is volatile and loses whatever is stored when

the computer is shut off.

Correct!

3.2.6 Secondary Memory• Also called Backing storage, it keeps all the information which isn’t

needed or too big for primary memory.• Software is stored in secondary memory• The two main ways of storing data on backing store are:

– Sequential Access– Direct Access

• Sequential Access: accesses data one record at a time– Ex. A payroll program has to access the data file containing all the data on all of a

company's employees. The data is accessed one after another or one at a time.

• Direct Access: the computer needs to locate an item quickly by moving directly to its record

– Also called random access– Ex. A supermarket where details of all of the items for sale are held in a file and

needed to be located quickly.– It requires a kind of index to be held on the material for holding the data.

Secondary Memory• Flash Memory:

– A solid state memory (no moving parts)– It is random access and writable– Non-volatile– Uses little power– Commonly known as flash drives

• Discs:– Two types of magnetic disks: hard disc, floppy disc– A disc pack has several plates of magnetic material arranged on a spindle.– The disc surfaces are divided into blocks each with a unique address

• CD’s and DVD’s:– The surface has lands and pits and the transition from on to the other is represented in binary

states– The bumps are read by reflected laser beams

• Tape:– Has a high storage density– Used for backing up network servers– Not a direct access medium– Mainly built for archiving high volumes of data

Secondary Memory ApplicationsDevice / Media Features and uses

Flash Memory Low power, non-volatile, fast direct access, re-writable. Can carry programs and data around in your pocket and plug into a computer (USB) when desired. Transferring digital photos, large documents, keeping backups. Typical size 128 Mb.

Discs Relatively high power and fragile, some types can be portable/swappable, most not very. Large capacity possible, direct access. Fast recovery of data. Still the main memory in most computers. Typical size 80 Gb.

Optical Media Larger capacity than Flash memory, smaller than hard disc. Rugged and portable, some types re-writable. Low cost. Readers are very widely available. Good backup medium but limited capacity relative to large networks. Typical size 700 Mb (DVD 2.7 Gb).

Tapes Larger capacity than all the others, with the possible exception of some hard disc arrays. Relatively cheap to manufacture. Serial access only. Good backup medium, especially for networks. Typical size 500 Gb.

How does sequential access work?

Accesses data one record at a time

A

B

D

C

Searches memory for a sequence of instructions

Finds information from a general index

Accesses information from the archives

Sequential Access accesses data one record at a time

Ex. A payroll program has to access the data file containing all the data on all of a

company's employees. The data is accessed one after another or one at a

time

Correct!

3.2.7 Function of a Microprocessor• The microprocessor is a discrete unit or integrated circuit formed by the CU

and the ALU.

• Each kind of microprocessor has its own instruction set.

– An instruction set is a set of commands which the microprocessor is designed to carry out.

• Each microprocessor has registers in a fixed size (the word size, typically 64 or 128 bit).

• The addition of Primary Memory makes a programmable machine since different programs can be loaded and run through the microprocessor.

• A microprocessor is in a machine that runs a fixed program such as:– A washing machine: the program controls the inlet and outlet valves, the heating

elements read data from an external panel that contains many controls.

• A microcontroller is a general purpose programmable microprocessor – It is fitted with RAM to hold temporary data from sensors, have output ports for actuator

interfaces to attach.

– It is in mice, keyboards, disc drives, etc.

– In a car it measures the fuel, operates the air conditioning, the ABS, and the airbag.

What is an example of the use of a microprocessor?

To measure the fuel consumption in a car

A

B

D

C

To control the keyboard

To gather information from the temperature sensors in a washing machine

All of the Above

Microprocessors are designed to carry out a set of command such as in a washing

machine, car or computer

Correct!

3.2.8 Input and Output Devices

Input Devices• Keyboard • Mouse • Touch Screen • OCR • MICR • Scanner (page, mark sense

and bar code) • Speech recognition • Sensors • Digital camera

Output Devices

• Printers • Plotters• Monitors• Robotics• Sound• LCD Panels

Device Feature Advantage Disadvantage Application

Mouse The movement of the mouse generates a series of pulses by which the computer can tell the direction of mouse movement.

Used to move a pointer on the screen to select a menu option or change and create different windows in a Graphical User Environment (GUI).Also easier to coordinate with the action on the screen.

Repeated use of the mouse may cause carpal tunnel syndrome

Allows the user to move a pointer on the screen to manipulate options on a computer

Keyboard A series of switches that each generate a series of different pulse codes to notify the computer what key was pressed

Typing and editing text on the computer and features short cut keys (function keys and numeric keypads ) to speed up common operations

Prolonged use may cause injuries such as repetitive stress injury (RSI) or carpal tunnel syndrome

entering and editing text into the computer

Touch Screen Screens that are used as both an input and output device

the options can be shown with text and or graphics and the position of a press on the screen can be detected

The touch screen may not be very accurate depending on the size of an icon in relation to the stylus or finger.

used where general information is being provided (banks, hotels, shopping centers) for users who may not be competent computer users

Device Feature Advantage Disadvantage ApplicationOptical Character Recognition (OCR)

Uses the principle of reflected light as a scanner passes a beam of light over a page and measures the reflected light. This gives a two-dimensional pattern of light and dark, which can be represented in binary.

The characters or drawings converted to a binary pattern can be sent as a string of electrical pulses to a fax machine or imported into a computer program.OCR can match the binary patterns to patterns stored in the computer's memory and each recognized character is then assigned its standard code (ASCII usually).

Prone to errors and has difficulties recognizing different fonts and handwriting

converts scanned document into text searchable files

Magnetic Ink Recognition (MICR)

The series of numbers at the bottom of a check are encoded with magnetic ink to be used with MIRC readers a banks

Has an increased reading speed and extra security against forgery compared to OCR. Also won’t be affected by dirty fingerprints and other marks.

MICR is more expensive than OCR and the amount has to be encoded in the blank space before the check is processed

Used to identify bank account details on a check

Scanner (page, mark sense and bar code)

• Mark Sensing: detects black marks on white paper• Bar code: read by emitting a light beam and detecting the amount of light reflected back; dark areas reflect less, light areas more)

Laser scanners are fixed and speed up the reading of barcodes

Page scanners only create an image of the text and are often slow

• Mark sensing is used on Scantrons • Libraries use the light pen to read bar codes and supermarkets use a laser scanner because it is fixed and scans faster

Device Feature Advantage Disadvantage Application

Speech Recognition

An application digitally records speech and matches the digitized patterns to the patterns of known words in the memory

The accuracy is at abut 90% for dictation to a word processing document

As there are various speech tones, accents, and pitches, the system has to be programmed with a standard set of words.

Dictation for a word processing document

Sensors A sensing device is connected permanently to a computer and the computer receives data from the sensor at intervals. Used to collect data when processes are automated.

This can be controlled with microprocessor applications instead of general purpose computers so that the program will be stored in ROM and very little RAM will be needed

Sometimes unreliable and can be easily set off unintentionally

Car washes, automatic washing machines, heating control in buildings, etc., uses sensors.

Digital Cameras

The data is compressed when storing and transmitting photographic images. A common standard is JPEG (Joint Photographic Experts Group)

Saves space and decreases transmission time. Also has better quality and prices compared to conventional cameras.

Consumes batteries quickly Can be used for video conferencing or to transfer picture from a camera to the computer

Graphic Tablets

A drawing board with a pen that has a magnet. Under the tablet is a grid of wires that locate the pen’s coordinates from pen’s movement causing disturbances in the electrical pulses in the wires.

The user has greater control over the resulting image

Coordination of the hand movements with the action on the screen is often difficult

Sophisticated computer art packages and video-editing systems for special effects

Device Feature Advantage Disadvantage ApplicationPrinters Classified by:

• Amount of text (character, line or page) • Character formation: (matrix vs. non-matrix)• Method of printing: (impact vs. non-impact)• Color: (black and white vs. color)

You can have a hard copy of text from your computer

Refilling ink and paper costs money

Types of printers:• Dot-matrix• Daisy Wheel• Lineprinter• Inkjet• Laser

Plotters • Electrostatic plotters make an image by burning special paper with a small spark.• Pen Plotters have several pens in different colors and draw on the page

They are able to plot on large sheets of paper precisely which can be a fixed size (flatbed plotters) or on a large roll of paper (drum plotters) and give a higher quality output

• Prints very slowly• Not able to print photo quality images• expensive• take up a lot of space

commonly used in industries such as science, architecture and graphic design

Monitors /Video Display Unit (VDU)

• Monochromatic or polychromatic• The resolution of a VDU is a function of the number of pixels on the screen itself and each pixel requires a memory location about its state.

Allows you to see what you are doing on the computer

Polychromatic VDU's require more memory to store information about the state of the screen

High resolution monitors (Graphical Display Terminals or GDU's) are used in special applications such as cartography, commercial graphics and design work.

LCD Panels Liquid Crystal Display Consumes very little amount of power, they are lighter weight, flatter , thinner and give out virtually no radiation compared to conventional CRT's

Doesn’t perform well in low lighting so it has to be backlit

Found on small computers and battery operated devices such as PDA’s

Which of the following is an example of an output device?

Speech RecognitionA

B

D

C

OCR

Plotter

MICR

The plotter is like a very large printer.

Correct!

Plotters • Electrostatic plotters make an image by burning special paper with a small spark.• Pen Plotters have several pens in different colors and draw on the page

They are able to plot on large sheets of paper precisely which can be a fixed size (flatbed plotters) or on a large roll of paper (drum plotters) and give a higher quality output

• Prints very slowly• Not able to print photo quality images• expensive• take up a lot of space

commonly used in industries such as science, architecture and graphic design

3.2.9 Recent Developments in Computer Architecture

Single Pipeline

• instruction can be fetched and another decoded while the first is still executing

• In each cycle, the instruction is decoded and executed, then a new one is fetched

Multiple Pipeline

• Pipelines work in parallel to maximize the rate of processing instructions

• It depends if the program has long sequences of instructions or is branched out. Then the entire pipeline will have to be “flushed.”

Processor Architecture

Supercomputers and mainframe computers use multiple processors to share the workload such as in Deep Blue and Cray supercomputers where massively parallel architecture is employed.

Recent Developments in Computer Architecture

The advances in modern technology called for a ROM that could be upgraded in the component itself. New technology such as scanners, CD-writers and digital cameras are now fitted with Flash ROM so the program can be changed by downloading the appropriate software from a website.

Primary Memory

Secondary MemoryNew storage media for portable devices such as digital cameras and MP3 players include:

Smart MediaCompact FlashMemory StickMultimedia Card

These storage media has non-volatile memory and are small with lower power consumption.

What is the significance in the advancement of Flash ROM?

It could be upgraded or modified in the component itself

A

B

D

C

It allows digital cameras to have a brighter flash

It uses less battery power

It increases the amount of information you can upload to a website

Flash ROM could be upgraded in the component itself. New technology such as scanners, CD-writers and digital cameras are now fitted with Flash ROM so it is rewritable.

Correct!

Please Try Again

Debacle

Epic FailFracasar

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Bibliography• http://cnx.org/content/m29369/latest/• http://computer.howstuffworks.com/bytes1.htm• http://ib-computing.net/html/program/core/architecture.html#bits• http://ib-computing.net/html/program/core/architecture.html#storage• http://www.ehow.com/list_5997493_advantages-disadvantages-

touch-screens.html• http://www.jegsworks.com/lessons/lesson3/lesson3-3.htm• http://www.ehow.com/list_6082165_advantages-disadvantages-

graphics-tablets.html• http://www.investintech.com/resources/articles/ocrprogram/• http://www.ehow.com/list_6001586_disadvantages-scanners.html• http://www.ehow.com/list_6309661_disadvantages-plotter.html• http://ib-computing.net/html/program/core/memories.html• http://ib-computing.net/html/program/core/recent.html