Arab Open University - AOU

Arab Open University - AOU
Information and Communication Technologies: People and Interactions Fourth Session Prepared by: Eng. Ali H. Elaywe

Prepared by: Eng. Ali H. Elaywe
Introduction Book S gives a brief overview of Communication Systems and Computer Systems Now it is time to dive a little deeper in the details of these systems. Book T consists of three parts Part 1: The technology of personal digital assistants  to be covered in this tutorial Part 2: The technology of the Internet, and the World Wide Web Part 3: The technology of mobile telephony Prepared by: Eng. Ali H. Elaywe

Aims Part 1 of Book T discusses the main parts of a computer systems with emphasis on PDAs (the technology of Personal Digital Assistants) These parts are hardware for input and output, memory, processors, and software Prepared by: Eng. Ali H. Elaywe

Reference Material This tutorial is based on the following references: 1- Part1 of Book T: Technologies 2- Also we refer to the T529 ICT CD-ROM 3- Finally we refer to the Book D: Documents Prepared by: Eng. Ali H. Elaywe

Topic 1: Introduction to the technology of personal digital assistants
PDA can be considered as a Computer System; however small it maybe It consists of : 1- Hardware 2- Software Continue Prepared by: Eng. Ali H. Elaywe

1- Hardware That is, the collection of physical components which constitutes the computer Essentially consists of 3 major buildings blocks namely: A- The Central Processing Unit (CPU) B- The Memory Unit C- The I/O Unit Continue Prepared by: Eng. Ali H. Elaywe

Examples of PDAs Hardware (Activity 1.3 ): 1- The Psion Revo (see Figure 1.A & Table1) A- CPU Information: This PDA is built around the ARM 710T Microprocessor B- Memory Unit Information: 8 MB of RAM, 8 MB of ROM C- I/O Unit Information: 53-key keyboard , speaker and a greyscale touch-sensitive screen Web site: 2- The Palm IIIc (see Figure 1.B & Table1) A- CPU Information: This PDA is built around the Dragon Ball EZ 20 MHz Microprocessor B- Memory Unit Information: 8 MB of RAM, 2 MB of ROM C- I/O Unit Information: buttons, buzzer and a 256-colour TFT touch-sensitive screen Web site: Continue Prepared by: Eng. Ali H. Elaywe

Figure 1.A The Psion Revo Figure 1.B The Palm IIIc Continue Prepared by: Eng. Ali H. Elaywe

Input–output peripherals
Input peripherals Output peripherals Input–output peripherals Processor Memory 1- Psion Revo (Figure 1.A) 53-key keyboard speaker 480 × 160 greyscale touch- sensitive screen (with stylus for input) infrared port docking cradle optional travel modem ARM 710T 32-bit 36 MHz RISC 8 MB RAM 8 MB ROM 2- Palm IIIc (Figure 1.B) buttons buzzer 256-colour 160 ×160 TFT touch-sensitive screen (with stylus for input) infrared link docking cradle DragonBall EZ 20 MHz 8 MB RAM 2 MB ROM Table 1 Psion Revo and Palm IIIc PDAs Prepared by: Eng. Ali H. Elaywe Continue

2- Software The hardware cannot of itself perform any tasks. It is only when software acts in collaboration with hardware that the computer can do its job So the software is: The program, or collection of programs, which enables the computer to carry out its tasks Program a collection of integrated and interdependent sets of detailed, step-by-step instructions that has been put together to tell a computer what function to perform The software for a PDA may consist of its Operating System and various Word Processing, Database and Games programs etc Prepared by: Eng. Ali H. Elaywe Continue

Examples of PDAs software: The PDA name: The Palm IIIc Operating System Software: PalmOS v.3.5 General Purpose Software: Diary Address Book Off-line mail reader and composer Games programs Prepared by: Eng. Ali H. Elaywe Continue

Activity 1.4 (self-assessment / revision) (a) What is a binary code? A binary code is simply a group of binary digits (also known as ‘bits’) – that is, of 1s and 0s (b) How do binary codes relate to bits and bytes? A binary code is made up of bits. A binary code that occupies just one byte will be 8 bits long, because there are 8 bits in a byte (c) Briefly state how each of the following can be represented as binary codes: (i) numbers Numbers are often represented as binary codes simply by converting the number to its binary equivalent. Thus 2 is 10 in binary code; 15 is 1111; 125 is ; and so on Prepared by: Eng. Ali H. Elaywe Continue

(ii) text Text is usually represented by a sequence of ASCII stands for American Standard Code for Information Interchange In its standard form of 7 bits it allows for 127 different characters, which is enough for the Latin alphabet, punctuation marks and numerals It has various extended forms (8 bits, 255 characters) to allow for accented characters, etc Each code representing either an individual letter or a character such as a space, an apostrophe or a digit Prepared by: Eng. Ali H. Elaywe Continue

(iii) a line drawing A simple line drawing may be represented in the same way as a full-colour picture (see part (iv) below) But a simpler way is to describe where the lines on the drawing are in some pre-defined way and convert this description to a binary code Some further information is needed, for instance line thickness and colour, and again this can be provided by use of binary codes (iv) a full-colour picture A full-colour picture can be represented by dividing the picture up into tiny squares called pixels or pels and then assigning to each pixel a binary code that describes its colour and brightness Prepared by: Eng. Ali H. Elaywe Continue

(v) sounds, both spoken words and music Sounds, whether speech or music, can be represented by first taking short, equal duration samples of the sound and then using a code to represent the characteristics of each of these samples (vi) computer instructions in a program Computer instructions in a program are represented by binary codes that have been laid down by the manufacturer of a particular processor at the time the processor was designed Continue Prepared by: Eng. Ali H. Elaywe

Binary number system (This material from T529 ICT CD-ROM) The number system with base 2 (uses two values 0,1) Our conventional number system, the denary system, uses base 10 (uses ten values 0, 1, 2, 3, ...9) The fact that binary digits can have only one of two states makes the binary system very suitable for use in electronic computation, data storage (electronic memory) and communications. In these fields, circuits that can exist in one of only two electrical states (represented by 0 and 1) are simple to design and can be mass produced N bits is suitable to present 2N denary numbers from 0 to 2N – 1 For Example, 8 bits is suitable to present (28 = 256) numbers from 0 to 255 Continue Prepared by: Eng. Ali H. Elaywe

Example Try to find the denary equivalent of ? (1 × 27) + (1 × 26) + (0 × 25) + (0 × 24) + (1 × 23) + (1 × 22) + (0 × 21) + (1 × 2 0) = = = 205 in denary The leftmost bit is called the most-significant bit and the rightmost bit is called the least-significant bit Continue Prepared by: Eng. Ali H. Elaywe

230 –128 102 –64 1 38 –32 6 –16 ... –8 –4 2 –2 –1 Converting from denary to binary Try to convert 230 denary number to 8-bit binary number? 2 7 (128) 2 6 (64) 2 5 (32) 2 4 (16) 2 3 (8) 2 2 (4) 2 1 (2) 2 0 (1) The binary number can then be read off from top to bottom; it is Continue Prepared by: Eng. Ali H. Elaywe

Hexadecimal system (this material from T529 ICT CD-ROM) The positional number system using as its base the number 16 The first ten numbers in hexadecimal are represented by the numerals 0, 1, 2, 3, …,9 exactly as in denary numbers. The next six numbers, equivalent to the denary numbers 10–15, are represented by A–F The hexadecimal system is often used in computer applications Continue Prepared by: Eng. Ali H. Elaywe

Hexadecimal numbers and their denary and binary equivalents
0000 1 0001 2 0010 3 0011 4 0100 5 0101 6 0110 7 0111 8 1000 9 1001 A 10 1010 B 11 1011 C 12 1100 D 13 1101 E 14 1110 F 15 1111 16 1 0000 17 1 0001 Prepared by: Eng. Ali H. Elaywe

Converting from Hexadecimal to denary Example Find the denary equivalent of hexadecimal EB7 ? = (E × 162) + ( B × 161) + (7 × 160) = (14 × 162) + (11 × 161) + (7 × 160) = (14 × 256) + (11 × 16) + (7 × 1) = 3767 Continue Prepared by: Eng. Ali H. Elaywe

hexadecimal and binary conversion (very easy) Hexadecimal notation provides a compact way of representing large binary numbers, as each group of four binary digits can be represented by a single hexadecimal number Example1: converting from binary to hexadecimal Try to represent the binary number as a hexadecimal number, first group the number into 4-bit groups as following: Now convert each 4-bit binary number to its hexadecimal equivalent: So is equivalent to BE If the binary number is not divisible into four-digit groups (for example, if it has 7 bits), leading zeros are added to make the number of bits into a multiple of four Prepared by: Eng. Ali H. Elaywe Continue

Example2: converting from hexadecimal to binary Try to represent the Hexadecimal number AF7 as a binary number? 1) Find binary representation (4-bit) of each hexadecimal number separately: A is equal to 10 = 1010 F is equal to 15 = 1111 7 is equal to 7 = 0111 2) Put these binary representation in correct order: A F So the result is: Prepared by: Eng. Ali H. Elaywe Continue

Activity 1.5 (self-assessment / revision) (a) What is meant by (i) Error detection Error detection is a process whereby pieces of binary data are checked while they are being manipulated or transmitted, in order to discover whether an error has occurred, If an error is detected, a special action usually follows: for example a request for retransmission of the binary data, or the display of an error message (ii) Error correction: If an error is detected (in erorr detection), it is corrected Error detection and correction used both for computer systems (e.g. data storage) and digital communication systems (transmission and reception of digital data) Prepared by: Eng. Ali H. Elaywe Continue

(b) What is meant by a ‘parity bit’? A parity bit is an additional bit put at either the beginning or the end of a binary code In an even-parity system the parity bit is chosen so that it will make the total number of 1s in the binary code (including the parity bit) even In an odd-parity system, the parity bit is chosen to make the total number of 1s odd (c) In an even-parity system, which of the following bytes must contain an error? (i) (contains an error because it has an odd number of 1s) (ii) and (iii) (not contan an error) (d) Does a parity check provide error detection or error correction? Error detection Because it is not possible to determine which bit is in error So More sophisticated methods are needed for error correction Prepared by: Eng. Ali H. Elaywe Continue

Hamming code (this material from T529 ICT CD-ROM) It is a simple technique for error correction The Hamming code uses redundant bits in such a way that when an error occurs the redundant bits indicate where it has occurred Here we are suppose that we have 4-bit code (A,B,C,D The trick is to add three redundant bits, called X, Y and Z, to each 4-bit pattern ABCD in such a way that if an error occurs in any one of the resulting seven bits the receiver can calculate where the error must have been. The receiver can therefore correct the error without any more help from the transmitter Prepared by: Eng. Ali H. Elaywe Continue

A- The Job of the sender: Suppose that the message to be sent is the number 2 (0010 in binary). Then A is 0, B is 0, C is 1 and D is 0 The four bits ABCD are taken in groups of three, BCD, ACD and ABD and an even parity check bit is calculated for each group Let X represent the parity check bit for BCD, Y the parity check bit for ACD and Z the parity check bit for ABD. The group BCD is 010 so the even parity bit X will be 1, because that makes the number of 1s even Group ACD is 010, so Y will be 1 Group ABD is 000, so Z will be 0 So Bits X, Y and Z are now attached to the original code ABCD to form a seven-bit code word ABCDXYZ. In the example, the word is and this is the code word transmitted Prepared by: Eng. Ali H. Elaywe Continue

B- The Job of the reciever When seven-bit code arrives, is to carry out even-parity checks on the groups BCDX, ACDY and ABDZ. The receiver checks whether each of the groups BCDX, ACDY and ABDZ has an even number of 1s. If none of the groups fail this parity check, then no error has occurred in transmission and the redundant bits can be ignored If all three parity checks fail, the source of the error must be bit D, since only bit D appears in all three parity-check groups The table2 below show the eight possible situations of the even-parity checks on BCDX, ACDY and ABDZ. If a check fails it is recorded as a 1 in the appropriate column, and if it succeeds it is recorded as a 0. Thus the first row (0,0,0) indicates that even parity was found on all three checks The bottom row indicates that all three even-parity checks failed Prepared by: Eng. Ali H. Elaywe Continue

Parity check results on
Location of error BCDX ACDY ABDZ No error 1 Z Y A X B C D Table2: Completed outcomes of even-parity checks on BCDX, ACDY and ABDZ, The fourth column is intended to indicate where the error, if any, must be in the signal ABCDXYZ Back Prepared by: Eng. Ali H. Elaywe Continue

Activity (this material from T529 ICT CD-ROM) What numbers were being transmitted (correct in even parity) when the following two 7-bit patterns were received? (a) BCDX (i.e. 0011) is even (no error) ACDY (i.e. 1010) is even (no error) ABDZ (i.e. 1010) is even (no error) So there are no errors and the number transmitted was 1001 (the number 9) (b) ACDY (i.e. 1011) is odd (error) ABDZ (i.e. 1011) is odd (error) So there is an error in bit A, the correct signal is therefore , and the number transmitted is 0001 (the number 1) Prepared by: Eng. Ali H. Elaywe Continue

Activity 1.6 (Journal) At the end of Section 7 of Book S, Systems I suggested that you made a note in the Workbook section of your Journal of anything about computer systems that you found puzzling or did not understand after studying that section. If necessary, look back to your notes on that point now to remind yourself of what you wrote. Bear this in mind as you study the rest of this part of Book T. Hopefully you will find answers to any questions as you study. But you may find that your study raises other questions. Note them. How will you find answers? Try to think of possible ways, and then use them Try to do this activity by your self Prepared by: Eng. Ali H. Elaywe

Topic2 : Hardware for Input and Output
1- Keyboards, keypads and buttons Purely input devices When the user presses a key or button, a switch under that key or button is closed and so an electric current can flow This produces an electrical signal, but not one in a form which the processor can recognize !!. That is why there is an input subsystem associated with the keyboard, keypad or set of buttons The task of this subsystem is to detect which key or button has been pressed from the electrical signal produced and then to generate an associated binary code (usually one byte long) which is unique to the key or button and which will be recognized by the processor (see figure 2) Prepared by: Eng. Ali H. Elaywe Continue

Figure 2 From user to processor via a key or button Continue Prepared by: Eng. Ali H. Elaywe

2- Liquid-crystal display (LCD) screen Purely visual output device Firstly used in portable computers (also known as notebook computers) Then used on desktop computers Liquid-crystal display screen contains a thin film of a liquid called a liquid crystal. This liquid is one which, at the molecular scale, has some of the regularity found in crystalline solids. Liquid crystals have rod-shaped molecules which can be aligned in various ways. When a voltage is applied across a thin film of liquid crystal, the molecules change their alignment Continue Prepared by: Eng. Ali H. Elaywe

A- Monochrome LCD The passage of light through the liquid crystal is partially or wholly blocked LCD displays may be ‘back-lit’, which means that they have a light source behind the screen Areas of the film where no voltage is applied then appear light while those where a high enough voltage is applied appear dark. Shades of grey can be produced by choosing appropriate voltages between relatively low (pale grey) and relatively high (dark grey). By applying different voltages to different areas on the screen, the transparency of the crystals is modified in those areas to create the required greyscale image on the screen Continue Prepared by: Eng. Ali H. Elaywe

Some LCD screens replace the backlighting with a mirror which reflects the ambient light Such displays usually provide a poorer contrast between dark and light areas, and are harder to see at an angle, but they do have the advantage in PDAs of consuming less power so that the battery lasts longer To create the different voltages required for each area – that is, each pixel – on a LCD screen, a system called ‘matrix addressing’ can be used, as in Figure 3. A signal is applied to each individual pixel by applying an appropriate voltage to both the row and the column which contain it Continue Prepared by: Eng. Ali H. Elaywe

Figure 3 The selection of one pixel in the array of a LCD screen. Note that the liquid is one continuous film; the pixels are defined by the electrodes between which the voltage is applied Prepared by: Eng. Ali H. Elaywe Continue

B- Active LCD An improved display, with no possibility of flicker, can be obtained by using an ‘active’ LCD screen In which each pixel is individually switched, using a thin-film transistor (TFT) So active LCDs are also described as TFT displays The use of a TFT for each pixel improves the quality of the display Disadvantage: Because of more complex circuitry is needed active LCD screens are more expensive than ‘passive’ ones Continue Prepared by: Eng. Ali H. Elaywe

C- Colour LCD screens Colour LCD screens have trios of pixels, each pixel having either a red, a green or a blue filter in front When a pixel is illuminated, it looks red, green or blue because the light must pass through the filter on its way to the user. Because all colours can be made up from different combinations of red, green and blue light, any desired shade or colour can be produced by illuminating, in different intensities, the pixels in a trio The task of the output subsystem associated with a LCD screen is to take data from the processor, which will supply information about the colours and patterns required on the screen. Then subsystem will turn this data into the voltage signals which are required to energize the appropriate pixels on the LCD screen Prepared by: Eng. Ali H. Elaywe Continue

Comparison between monochrome and colour LCDs 1- In monochrome LCDs, battery life is conserved by using a liquid-crystal layer which is normally transparent. This is because usually most of a screen is light (e.g. black text on a white background) and so energy is only being used to generate the smaller proportion of the display on the screen 2- But in colour displays the liquid-crystal layer must be normally dark and be turned transparent when a voltage is applied. Colour LCD screens thus tend to consume more power than monochrome ones Continue Prepared by: Eng. Ali H. Elaywe

Activity 1.8 (self-assessment) Draw an equivalent diagram to Figure 2 to represent a LCD screen as an output peripheral Prepared by: Eng. Ali H. Elaywe Continue

3- Touch-sensitive LCD screen (touch screen) input–output peripheral The user indicates inputs by touching an appropriate area on the screen Touching a particular spot on the screen usually acts in the same way as would clicking with a mouse when the cursor (the little arrow) is over the appropriate spot on a desktop computer’s monitor There are two different methods of making a screen touch-sensitive: Continue Prepared by: Eng. Ali H. Elaywe

A- The user touches a sheet of a type of clear plastic called mylar which is separated very slightly from the sheet of clear glass at the front of the LCD screen by tiny separators which are almost invisible The user’s touch brings the mylar sheet into contact with the glass sheet, and as both surfaces are coated with a transparent conductive layer. Detectors at the edge of the screen, together with a suitable controller, are then able to ascertain the co-ordinates of the point where the user touched the screen B- The other type of touch-sensitive screen consists of only one layer and so has the advantage of not reducing the visibility of the LCD screen behind it as much. This single layer is sheet of clear glass at the front of the LCD screen When the user touches the glass, the finger absorbs some of the sound. This is detected by detectors and again a controller is able to ascertain where the user touched the screen Prepared by: Eng. Ali H. Elaywe Continue

Note In both cases of Touch-sensitive LCD screen, an associated input subsystem has to convert the electrical signal from the controller into data that the processor can recognize as giving a position on the screen Continue Prepared by: Eng. Ali H. Elaywe

4- Buzzers and Loudspeakers A- Some PDAs have a buzzer which is used to produce one or more warning or confirmatory ‘beeps’ B- A few expensive models have a loudspeaker which can reproduce a wider range of sounds including speech and music Sound: All sound is produced by something vibrating. When you talk your vocal cords vibrate, as does the air in your throat, mouth and even nose Continue Prepared by: Eng. Ali H. Elaywe

The faster the vibrations occur, the higher the pitch of the note The rate of the vibrations is referred to in music as the pitch and in science and technology as the frequency Frequency is measured in a unit called hertz (abbreviation Hz). Thus a vibration rate of, for example, 500 per second is referred to as a ‘frequency of 500 Hz’ A louder sound is produced when the vibrating object moves to and from through a greater distance The term ‘intensity’ is sometimes used instead of ‘loudness’ when describing sound Continue Prepared by: Eng. Ali H. Elaywe

A- The buzzers in PDAs consist of a tiny piece of ceramic which has the property that it changes shape slightly when a voltage is applied across it Such a ceramic is described as being a piezoelectric ceramic, and a suitable electrical signal can make it vibrate fast enough that it produces an audible ‘buzz’ B- For reproducing speech or music, the most common type of loudspeaker is one where sound is produced by a cone that is made to vibrate by an electrical signal. The faster the cone vibrates, the higher the frequency of the sound it produces This kind of loudspeaker is known as a ‘moving coil loudspeaker’ Continue Prepared by: Eng. Ali H. Elaywe

The task buzzer or loudspeaker output subsystem is to convert the data from the processor into an appropriate electric current A- In a PDA with a buzzer, typically offering a few ‘beeps’. So the processor will supply the output subsystem with only a few different data values B- In a PDA with a loudspeaker, The output subsystem needs to be more sophisticated. This is because the subsystem will need to convert sample values representing the sound (which will have been stored in the PDA’s memory and passed to the subsystem via the processor) into the appropriate electrical signals to drive the loudspeaker. So the memory of the PDA will also need to be larger, to store the samples Continue Prepared by: Eng. Ali H. Elaywe

5- Infrared transmitters and receivers One important I/O task for PDAs is to use infrared signals in order to send data to, and receive data from, other PDAs and/or desktop computers, to send data to printers, to access the Internet via a mobile phone, etc For this purpose they use an infrared transceiver (a device containing a transmitter and receiver units is called a transceiver) Continue Prepared by: Eng. Ali H. Elaywe

The Infrared Data Association (IrDA) has created a standard for infrared transmission between objects such as handheld devices If a manufacturer designs the infrared facilities of a PDA or mobile phone to conform to the IrDA standard then it should be able to interwork with other IrDA-compliant devices Unfortunately, there are slightly different versions of the IrDA standard in use and so full interworking is not always possible Continue Prepared by: Eng. Ali H. Elaywe

6- Docking Cardless: When the PDA is placed in its docking cradle an interconnection is made by cable to the desktop computer and data is exchanged In this way a diary on the desktop computer can be kept identical to one on a PDA. For example Docking cradles are usually connected to the type of connector at the back of a desktop computer known as a serial port Until very recently the most common type of serial port on desktop computers has been designed to a standard known as RS232 More recently a newer standard (defacto standard for serial port) known as USB (universal serial bus) are used Continue Prepared by: Eng. Ali H. Elaywe

Activity 1.10 (exploratory) Both the PDA and the desktop computer are computers, and both manipulate binary data. Can you think of a reason why the data is not simply transferred directly between them, without conversion to the RS232 or USB format? Because There are two problems with direct transfer 1- The voltage levels and speed of data transfers inside the PDA are not necessarily compatible with those inside the desktop machine 2- The other problem is that data needs to be fed into and taken from the desktop computer. Desktop computers come with a limited number of places where this can be done, and normally none of these is designed specifically for direct data transfer to and from a PDA. On the other hand, they do normally come with at least one port compatible with either RS232 or USB. The manufacturers of the PDA can therefore safely assume that the purchaser will be able to use any desktop computer to exchange data with their PDA Prepared by: Eng. Ali H. Elaywe

Topic 3: Memory The Memory Unit in a computer system is used to store programs and data There are two types of memories: 1- Main Memory 2- Secondary Memory Continue Prepared by: Eng. Ali H. Elaywe

Topic 3: Memory 1- Main Memory Main memory consists of one or more integrated circuits or chips As the technology of integrated circuits advances, so more and more memory can be put on a single chip This is one of the advances that have made handheld and palmtop PDAs possible Main memory can be thought of as a set of numbered ‘slots’ called memory locations, or just locations The numbers identifying the locations are known as memory addresses, or just addresses All memory locations hold exactly the same number of bits, and the groups of bits that will fit into data locations are often known as data words, or just words. Most PDAs use 16-bit or 32-bit data words Continue Prepared by: Eng. Ali H. Elaywe

Bit: is the smallest information units, hence can not represent much information Byte: is the basic unit which is passed around the computer, hence can represent more information than a single bit Each 8-bit unit is called a byte Kilobytes: 210 = 1024 bytes (Example: A file is 45 Kbytes) Megabytes: 220 = 1,048,576 bytes (1024*1024) (Example: A computer has 256MB of RAM) Gigabytes: 230 bytes (1024*1024*1024) (Example:A computer has 40GB of hard disk) Continue Prepared by: Eng. Ali H. Elaywe

Writing and Reading process The process of storing data in a particular location in memory is known as writing During a write operation the processor first sends to the memory the address of the location to be written to and then sends the data word that is to be written into that location. And of course it must ‘tell’ the memory that it is a write operation The process of retrieving data from a particular location is known as reading During a read operation the processor sends to the memory the address of a location and receives back a copy of the data word held in that location. And again, it must ‘tell’ the memory that it is a read operation. So writing to a memory location overwrites whatever was there before, but the data stored in a memory location is unchanged when it is read Continue Prepared by: Eng. Ali H. Elaywe

Address bus and data bus The address bus carries addresses from the processor to the main memory The data bus carries data words between the processor and the main memory The data bus can carry data words in either direction and so is known as a ‘bidirectional bus’, whereas the address bus carries addresses in only one direction and so is known as a ‘unidirectional bus’ Two sorts of memory integrated circuits are used for main memory, A- ROMs and B- RAMs Continue Prepared by: Eng. Ali H. Elaywe

A- ROMs (Read Only Memory) The name refers to the fact that this is a type of memory whose contents cannot be changed by the processor after the memory integrated circuit has been installed in the computer The processor can examine (read) the ROM’s contents, but not change (write to) them (non volatile) Example: BIOS Computer built-in instructions to load the operating system when the computer starts up On the other hand, there are some sorts of ROM, such as ‘Flash’ ROM, where the user can change the contents (write to) Continue Prepared by: Eng. Ali H. Elaywe

B- RAM (Random Access Memory) RAM, can be both written to and read from by the processor This name (Random Access Memory) arises from the fact that the data in any location in the whole memory can be accessed just as quickly as the data in any other location (In fact, ROM is also random-access, but the terminology is now so widespread that it is firmly established, even if not wholly unambiguous.) An important point about RAM is that it is usually ‘volatile’, which means that the data stored in it is lost when the power supply to the RAM is switched off. This contrasts with ROM and secondary memory, which are non-volatile Continue Prepared by: Eng. Ali H. Elaywe

Important Note If you look back to the brief specifications of the Palm IIIc and Psion Revo in the boxes on pages 6–8, you will see that each has both ROM and RAM In these PDAs, which do not have any secondary memory: The ROM is used to hold the programs and data supplied by the manufacturer While the RAM is used to hold the user’s own data plus any additional programs that the user may have been able to install Continue Prepared by: Eng. Ali H. Elaywe

2- The secondary memory It holds data and programs not in active use Examples: The hard disk, floppy disks, CD-ROMs and DVDs Very few PDAs, however, include any secondary memory as standard, though some do offer it as an optional extra. If a PDA does offer secondary memory, the most likely type is a memory card, also known as a PC card. These small cards can contain additional programs and associated data and fit into a special slot in the PDA’s housing As memory cards can hold several hundred megabytes of program and/or data (even as much as a gigabyte, at a price!) they offer a significant increase in the potential number and size of programs in a PDA, and/or in the amount of data that can be accessed by the PDA So the use of such memory cards can greatly increase the flexibility of a PDA Prepared by: Eng. Ali H. Elaywe

Topic 4: Processors A processor is the brain of a PDA or any other computer system In its simplest form, it consists of: 1- ALU (arithmetic and logic unit) performs the arithmetic (addition, subtraction, multiplication etc.) and the logical operations 2- The control unit as usually concerned with the program execution and control 3- The register is a storage element which is part of the processor itself, as distinct from the locations of main memory. Also the instructions in the program must refer to the internal registers of the processor A processor may have anywhere from 8 to 32 registers Continue Prepared by: Eng. Ali H. Elaywe

The program resides in memory and an instruction Fetch-Decode-Execute cycle is used to describe the process of reading a program instruction from memory, decoding that instruction and then performing the task corresponding to that instruction Examples of instructions used in processors: 1- Read a data word from memory location 29 and put it into register 1 2- Send the data word currently in register 5 to output subsystem 3 3- Add the number in register 2 to the number in register 1 and put the result in register 3 4- jump over the next 5 instructions if the number in register 3 is zero Instructions that the processor understands directly are called Machine/Assembly Language instructions Programmers usually write programs in a higher level language such as C/C++ etc Prepared by: Eng. Ali H. Elaywe Continue

What does the processor do to add two numbers in M1 and M2?? Load AX,M1 Read a data word from memory location M1 and put it into register AX ADD BX,M2 Add the number in register BX to the number in memory location M2 and put the result in register BX STORE M3,BX Store the result in memory location M3 Prepared by: Eng. Ali H. Elaywe Continue

The Instruction sets: The term ‘instruction set’ is used to refer to the complete set of instructions a processor can execute The processor come equipped with different sets of instructions that they are able to execute! Why the processors have different sets of instructions? The answer is that all of these features significantly affect the performance of the processor Hence manufacturers vie with each other to find an architecture and instruction set that give their processor an edge over all others Prepared by: Eng. Ali H. Elaywe Continue

RISC (Reduced Instruction Set Computer) instruction sets of processors were becoming larger and larger. They were including more complex instructions which were designed to carry out more complex tasks. In fact, some research showed that processors spent around 80% of their time executing only around 20% of the instructions in the instruction set But including these complex instructions in the processors made them harder to design and more expensive to produce So there was a fresh look at the design of processor architectures and instruction sets. This fresh look led to RISC (Reduced Instruction Set Computer) processors RISC processor have a small and simple set of carefully chosen instructions RISC processor is faster and consumes less power than its more complex cousins PDAs usually use RISC processor Prepared by: Eng. Ali H. Elaywe Continue

The speed of the processors Manufacturers often quote the ‘speed’ of their processors in megahertz (MHz) This ‘speed’ figure is an indication of how many instructions the processor can execute per second Why we did not need higher speed processors in the PDA?? 1- High speeds are not needed for the simpler, more limited tasks of a PDA 2- Faster processor would significantly increase the costs 3- Faster processors deplete a battery faster and so reduce battery life Continue Prepared by: Eng. Ali H. Elaywe

Does it imply that the speed of 30 MHz would perform a particular task faster than another processor at speed of 25 MHz? On the face of it, you might well assume that a processor with a quoted speed of 30 MHz would perform a particular task faster than another processor with a quoted speed of 25 MHz But things are not so simple!!!! remember, the architecture and instruction set of a processor significantly affect its performance So the 25 MHz processor may have a well-designed architecture and instruction set, then can perform any given task just as fast as the 30 MHz processor In fact, all that the number of megahertz really tells you is how fast instructions are fed to the processor, not how fast the processor will perform a given task Prepared by: Eng. Ali H. Elaywe

Topic 5: PDA Software The software for a PDA (or any other computer system) can be divided into two types: 1- Operating Systems 2- Application Programs Continue Prepared by: Eng. Ali H. Elaywe

Continue Prepared by: Eng. Ali H. Elaywe

Sub-Topic 5.1: Operating Systems Which are the basic set of programs without which the computer becomes difficult Operating system enables the computer to respond to the user’s inputs and to provide outputs to the user (I/O functions) The application programs’ are also handled by the operating system When a program needs to collect some data from the user it does not itself include the computer instructions to collect this data; instead it refers the task to the operating system, and the operating system performs the task on behalf of the application program Prepared by: Eng. Ali H. Elaywe Continue

So an operating system must take into account the particular processor that will be used, its architecture and its instruction set If there is any secondary memory then the operating system must take care of the transfer of data between the processor and that secondary memory Example 1: Operating System for the PCs The best known operating system for desktop computers is Windows Example 2: Operating Systems For PDAs There are two operating systems for PDAs: EPOC32 and PalmOS Continue Prepared by: Eng. Ali H. Elaywe

Activity 1.15 (explaratory) Can you think of any reasons why this is a good way of doing things? ( the advantages of the operating systems) 1- Make the user interface more friendly 2- It saves storage space in the memory. If each individual application program had to include the instructions for collecting data from the user then each program would take up more memory space and the memory would hold several copies of the same list of instructions. If all application programs call on the operating system to perform the task then the instructions are held only once in the memory. This is an important consideration in PDAs where memory space is at a premium Prepared by: Eng. Ali H. Elaywe Continue

3- This advantage is perhaps more relevant to desktop and notebook computers than to PDAs, is that if the hardware of the computer is changed – a new printer, perhaps – only the details of the operating system need to be changed. If each individual application program contained instructions for sending material to the printer then every application program would need to be updated when a new printer was installed – a very difficult task! 4- co-ordinate all the activities of the the various components of the computer system, and making sure that they are scheduled appropriately and there are no conflicts between them, Failure to do this will cause the system to crash!! Continue Prepared by: Eng. Ali H. Elaywe

Sub-Topic 5.2: Application programs These enable computer systems to perform particular tasks Examplen1: Application Programs for PC: Wordprocessor, spreadsheet, database, Web browsers etc A user can also write his own application programs using a computer programming language such as C/C++ Example 2: Application programs for PDAs: An electronic address book An electronic diary An electronic ‘to do’ list An electronic notepad Continue Prepared by: Eng. Ali H. Elaywe

Activity 1.18 (Journal) Here is an activity to prompt you to begin to work on ‘bringing it all together’ for small computer systems like PDAs. I suggest you write your answer in the Workbook section of your Journal. You may even want to write two versions of your answer, one to give an overview and the other to go into more detail Imagine that you have a PDA with a full keyboard and a monochrome LCD screen. You have the address book program running and you have just typed in the name of a new friend, John Smith, (without making any errors and so having to press the ‘delete’ key). Describe as fully as you can what activities have had to go on inside the PDA and in appropriate input and output peripherals while you were doing this. Also describe what will end up in the PDA’s RAM Try to do this activity by your self Continue Prepared by: Eng. Ali H. Elaywe

Topic 6: Preparation for Next Session 1) Read Part1 of Book T 2) Do all activities in Part 1 of Book T including links to Book C and Book D 3) Complete the Journal items related to Part 1 of Book T 4) Do activity 1.18 (Journal) 5) Skim Part 2 of Book T Prepared by: Eng. Ali H. Elaywe

Arab Open University - AOU

Similar presentations

Presentation on theme: "Arab Open University - AOU"— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

Arab Open University - AOU

Similar presentations

Presentation on theme: "Arab Open University - AOU"— Presentation transcript:

Similar presentations

About project

Feedback