Objective 1 Distinguish between true and false statements concerning the terms in the index for this block, or explain the terms in your own words.
Objective 2 Understand the need for a task to be broken down into a seqential list of simple, unambiguous instructions in order for a computer to be able to perform it.
Computer applications depend upon a task or tasks having been described completely and unambiguously in a way that the computer can understand and use. To specify tasks in such detail can be surprisingly difficult because of the complexitiy of human thought and the fac that a complete specification requires that all possible contingencies should be catered for.
Objective 3 Explain why it can be useful to partition a system into a set of subsystems; draw a structure diagram for a given system
SAQ4 (a) What do you think is the main factor that influences the way a system is partioned into subsystems
It's the complexity of the the interactions between the resulting subsystems.
(b) What is the major advantage of a partioning where the interactions between the subsystems are minimised and occur across well-defined interfaces.
It makes it easier to describe, understand, design etc. the system, because each of its component subsystems can be studied independently of the others.
See also SAQ2 answer, page 45 and SAQ3 answer, page 46.
Objective 4 State and briefly describe the roles of major hardware and software subsystems of a computer system and also of the computer itself; draw structure diagrams for these subsystems.
SAQ7 Write a brief description of the role played by each subsystem of a multimediadesk-top computer.
The input peripherals transmit data from the user to the computer, e.g.the keyboard enables the user to input data and commands to the computer; the mouse enables the user to input data and commands to the computer; the microphone enables the user to input data and perhaps commands to the computer.
The computer is the heart of the computer system and contains the processor and main memory. The input subsystem enables data to pass successfully from the input peripherals to the processor. The processor executes the programs and so carries out all the processing (e.g. calculations) on data. The main memory holds the program and associated data on which the processor is working. The output subsystem enables data to pass successfully from the processor to the output peripherals.
The secondary memory is used for the long-term storage of data and programs. Floppy disks and hard disks are both used to store programs and other data, but the storage capacity of a hard disk is much greater. CD-ROMs are also used to store programs and other data, but the user cannot change their contents (except in some newer versions).
The output peripherals transmit data from the computer to the user. The monitor and loudspeakers are means by which the computer can pass information to the user. The printer does the same, but this time the record is more permanent.
Objective 5 Identify the input and output peripherals of a given computer system; draw relevant structure diagrams.
SAQ 5 Classify each of the following as an input peripheral, an output peripheral, and input-output peripheral or secondary memory.
(a) a pair of stereo loudspeakers - output peripheral
(b) a microphone - input peripheral
(c) a modem - input-output peripheral
(d) CD-ROMs - secondary memory
Objective 6 Distinguish between general-purpose and dedicated computers; indicate the differences in their software and their input and output peripherals.
There are two main differences between general-purpose and dedicated computers.
(1) General-purpose computers are designed to be able to run a large range of software, whcih means that they can be used in a large range of applications, while dedicated computers are designed to run only the software appropriate to thier intended application.
(2) General-purpose computers always have some general-purpose input and output peripherals, even if they also have some special-purpose peripherals, while dedicated computers only have the input and output peripherals which are necessary for their intended application.
Objective 7 State the major hardware components of a computer and identify those that are usually housed in the system unit.
The components are: the system unit, the keyboard, the monitor, the mouse, the printer, the TMS board, the CD-ROM or floppy disks.
The system unit houses the processor, the main memory, the input subsystem, the output subsystem, the hard disk, the power supply or mains adapter, one or more floppy disk drives and possibly a CD-ROM drive and one or more loudspeakers.
Objective 8 Give reasons for having both main memory and secondary memory in a computer system; state what each is used for; describe the data flow between them when a particular task is carried out.
SAQ9 Summarise the reasons for having both main memory and secondary memory in a general-purpose computer system and state what each is used for.
(1) A program must be in main memory before the processor can execute it, but main memory is mroe expensive that secondary memory. It is therefore customary to store programs and other data in secondary memory then copy them to main memory when required.
(2) Most of main memory is volatile, i.e. it loses its contents when the power is switched off (except for ROM), whereas secondary memory can retain data without any power supply.
(3) Secondary memory in the form of floppy disks and CD-ROMs is a means by which software can be transferred from one computer to another and hence new softwarebe acquired.
SAQ8 A computer has a hard disk which holds a program to update records of customers' names, addresses and current orders. The hard disk also holds the records themselves. Describe the flow of data between the hard disk, the main memory and the processor when a user updates the record on a particular customer.
The program is copied from the hard disk into the main memory. The processor can now execute the program. The record to be corrected is then copied from the hard disk into the main memory.
The processor can now operate on this record in accordance with the user's commands and other input's to the program.
Finally the amended recorded is copied back onto the hard disk. The program itself will not have been altered, so doesn't need to be copied back.
Objective 9 State the three aspects of compatibility that an interface between an input, output or input-output peripheral and the system unit must provide and explain the advantages of standards and protocols in interfacing.
The three aspects of compatibility are:
a mechanical aspect
an electrical aspect
a data-transfer aspect
There are standards for mechanical and electrical compatability which means that the manufacturers of system units can supply some of the electrical and mechanical components inside the system itself. There are protocols for data-transfer compatability which lay down the rules of exchangeof data between subsystems.
Objective 10 Describe and compare the operation of a cathode-ray tube monitor and a liquid-crystal display screen.
SAQ10 List the similarities and differences between a monochrome monitor based on a cathode-ray tube and a monochrome LCD screen.
Similarities:
In both cases the screens are composed of timy elements - phosphor dots for CRTs and liquid crystals for LCDs
In both cases images are composed of pixels.
Differences
LCD screens are considerably smaller and lighter than monitors based on CRTs.
LCD screens comsume less power.
LCD screens are more expensive.
Screens based on CRTs can be made larger than LCD screens.
There is a wider viewing angle for screens based on CRTs than for LCD screens.
In a CRT monitor the phosphor dots are made to glow when a beam of electrons hits them. In an LCD screen the liquid crystals become opaque when half their required voltage is supplied on a row connection and hlaf on a column connection; hence an LCD screen needs a light source.
Objective 11 Describe and compare the operation of a dot-matrix printer, an ink-jet printer and a laser printer.
SAQ11 List the similarities and differences between a dot-matrix printer and a laser printer.
| Similarities | Differences |
| 1. Both produce characters which are made up with a matrix of dots | 1. Many more dots are used per character with a laser printer than with a dot matrix printer. This results in a sharper image. |
| 2. Both are available in either monochrome or colour | 2. In dot matrix printer a print head with raised dots presses an inked ribbon against the paper (impact). In a laser printer the characters are formed when tomer powder is attracted to the cylinder and then transferred to the paper (non-impact) |
| 3. Laser printers are normally quicker, quieter but more expensive. |
Objective 12 Briefly describe the operation of a mouse and of a keyboard.
A mouse is an example of a pointer device. It is used to move a pointer on the screen. Buttons allow the user to send signals to the computer.
A microcontroller in a keyboard scans the contacts under the keys and sends a signal to the system unit when a contact is closed (key is pressed) and again when it is opened (key is released). Codes are used to indicate which key has been pressed / released.
Objective 13 Distinguish between system software and application software and describe the interaction between them; give examples of application software.
SAQ12 Briefly explain what is meant by the terms "system software" and "application software". Give a couple of examples of system programs and application programs.
System software is the basic set of programs without which a general-purpose computer becomes unusable or very inconvenient to use. An example is Windows 95.
Application software is the name given to programs which enable the computer to perform specific tasks. An example is a word-processing or spreadsheet package.
SAQ13 You are using a spreadsheet application program to draw up some accounts. You want to print them. How will this application program interact with the system software? Now you want to save the accounts on a disk. How will this application program interact with the system software?
The application program (the spreadsheet) will invoke the program in the system software which prints a given set of data and will indicate the data that is to be printed and its format. The program in the system software will inform the application program when the task is complete and the application program will similarly inform the user.
The second interaction is similar except that the program in the system software which is invoked transfers data to a disk and updates the list it keeps of the documents on the disk.
Objective 14 State the main subsystems of an operating system and indicate which will be used during particular tasks.
SAQ15 (a) List the four subsystems of an operating system.
User Interfacing; Input-Output Control; Interrupt Control; Resource Supervision
(b) Which of these functions will be used as you perform the following steps:
(i) retrieve from a disk a file you had previously stored User intefacing and i/o control to accept your command; resource supervision to copy the file into main memory.
(ii) move the cursor through the text to locate a character that is to be changed User interfacing, i/o control and resource supervision; interrupt control if you use the keyboard rather than the mouse to move the cursor.
(iii) press the delete key to delete this character User interfacing, interrupt control and i/o control.
(iv) type in the replacement character User interfacing, interrupt control, i/o control
(v) save the amended file back on disk User interfacing and input-output control to accept your command; resource supervision to copy the file back to disk.
Objective 15 State the main functions of an operating system and indicate the ways in which they both insulate the user from many of the complexities of using a computer system and also insulate application software from the complexities of the hardware.
SAQ 14 An operating system (a) "insulates the application software from the complexities of the hardware (b) "insulates the user from the complexities of using a computer. What similarities are there between (a) and (b)?
In both cases the o/s offers facilities which either the user or the application software can invoke. When users use these facilities, they need to know nothing about how data is printed or displayed on the screen, how the computer handles characters typed at the keyboard, how data is transferred between secondary and main memory etc. Similarly when the application software uses these facilities, the software's programmers have no need to concern themselves with the details of how the hardware works.
Application software that interacts with the hardware only through the operating system can be readily transferred between computers that use the same operating system. A user that has learned to use an operating system can use any coputer that uses the same operating system.
The size of the application software programmer's task is reduced if the application software makes use of the facilities offered by the operating system. The size of the user's task to familiarise themselves with the computer is reduced if interaction with the computer is only through the operating system.
Objective 16 Describe and compare the user interfaces and facilities provided by DOS and Windows
MS-DOS has a command-line interface and prompts the user when it is waiting for an input. Windows provides a graphical user interface (GUI). The user points to an icon or a menu item on the screen and the clicks, drags an icon, etc.
Objective 17 Explain the use of files, folders (directories and subdirectories) in the storage of data in secondary memory.
Programs and other data are organised as files and each file is identified by a descriptive name. The o/s creates and updates a list of all the files on each disk which is stores on the disk with the files. This list is called a directory. It contains the names of the files and also the size of the file, the physical location on the disk and the date when the file was last modified.
Objective 18 Draw up and begin to answer some questions about how the hardware and software act together to enable the TMS to perform its task.
SAQ16 (a) How does the system "know" that I have pressed 'd' on the keyboard?
The application software is awaiting an input from you while the menu is displayed. It will therefore have made use of the operating system's input handling and will have requested the operating system to report any keypress to it. When you press the 'd' key the microcontroller in the keyboard detects the press and sends a signal to the microprocessor in the system unit. The oeprating system controls the collection of this code and its possing on to the application software.
(b) How does the appropriate action of the TMS follow from my keypress?
Each option on the menu has a program module associated with it. By implication, therefore, the receipt of the letter d (or, rather, the code for theletter d) causes the appropriate program module to be executed and this module effects the appropriate TMS action.