WAEC SSCE - Computer Studies - 2019 (Essay)
Question 1 Rapport
(a) A musician intends to record music on a storage medium. List four ways that the music file can organized in the storage medium.
(b) State two basic operations on computer file. (c) Explain the following computer terms: (i) file (ii) re cord
(a) Four ways a music (data) file can be organised on a storage medium:
- Serial organisation: records are stored one after another in the order in which they are created, with no particular key sequence.
- Sequential organisation: records are stored in a sorted order based on a key field (for example, by track number or title), so they can be read in that order.
- Random (direct) organisation: each record is placed at a storage address calculated from its key, allowing any record to be accessed directly without reading the ones before it.
- Indexed (index-sequential) organisation: records are stored in sequence but an index is also kept, so a record can be found either directly through the index or by reading in sequence.
(b) Two basic operations on a computer file:
- Reading (retrieving/opening) data from the file.
- Writing (saving/storing) data into the file.
Other acceptable operations: create, open, close, update/edit, delete, append, sort, search.
(c) Explanation of terms:
(i) File: A file is a collection of related records stored together under one name on a storage medium and treated as a single unit. For example, a file may hold all the records of a musician's songs.
(ii) Record: A record is a collection of related fields that describe one item or entity within a file. For example, in a music file a single record may hold the title, artist, duration and file size of one song.
Détails de la réponse
(a) Four ways a music (data) file can be organised on a storage medium:
- Serial organisation: records are stored one after another in the order in which they are created, with no particular key sequence.
- Sequential organisation: records are stored in a sorted order based on a key field (for example, by track number or title), so they can be read in that order.
- Random (direct) organisation: each record is placed at a storage address calculated from its key, allowing any record to be accessed directly without reading the ones before it.
- Indexed (index-sequential) organisation: records are stored in sequence but an index is also kept, so a record can be found either directly through the index or by reading in sequence.
(b) Two basic operations on a computer file:
- Reading (retrieving/opening) data from the file.
- Writing (saving/storing) data into the file.
Other acceptable operations: create, open, close, update/edit, delete, append, sort, search.
(c) Explanation of terms:
(i) File: A file is a collection of related records stored together under one name on a storage medium and treated as a single unit. For example, a file may hold all the records of a musician's songs.
(ii) Record: A record is a collection of related fields that describe one item or entity within a file. For example, in a music file a single record may hold the title, artist, duration and file size of one song.
Question 2 Rapport
(a) Explain the following terms: (i) storage device; (ii) virtual memory.
(b) Two storage devices have capacities 2KB and 2MB respectively. (i) Calculate the number of bits that each of 2KB and 2MB can hold. 2 KB: 2 MB
(i) Putting the two storage together, calculate the total capacity in bytes.
(a) Explanation of terms:
(i) Storage device: A storage device is a piece of computer hardware used to record (write) and hold (retain) data, instructions and information either temporarily or permanently, so that they can be retrieved (read) later. Examples include the hard disk, flash drive, memory card and optical (CD/DVD) disk.
(ii) Virtual memory: Virtual memory is a memory-management technique in which a portion of the hard disk (secondary storage) is set aside and used as an extension of the main memory (RAM). When the RAM becomes full, the operating system temporarily moves some data or program pages to this disk area, giving the impression that the computer has more RAM than it physically has. This allows large programs to run even when physical RAM is limited.
(b) Calculations
(i) Number of bits held by each device
Recall: \(1\text{ byte} = 8\text{ bits}\), \(1\text{ KB} = 1024\text{ bytes}\), \(1\text{ MB} = 1024\text{ KB} = 1024 \times 1024\text{ bytes}\).
2 KB:
\[2\text{ KB} = 2 \times 1024\text{ bytes} = 2048\text{ bytes}\]
\[= 2048 \times 8\text{ bits} = 16384\text{ bits}\]
2 MB:
\[2\text{ MB} = 2 \times 1024 \times 1024\text{ bytes} = 2097152\text{ bytes}\]
\[= 2097152 \times 8\text{ bits} = 16777216\text{ bits}\]
(ii) Total capacity of the two devices together, in bytes
\[2\text{ KB} = 2048\text{ bytes}\]
\[2\text{ MB} = 2097152\text{ bytes}\]
\[\text{Total} = 2048 + 2097152 = 2099200\text{ bytes}\]
Détails de la réponse
(a) Explanation of terms:
(i) Storage device: A storage device is a piece of computer hardware used to record (write) and hold (retain) data, instructions and information either temporarily or permanently, so that they can be retrieved (read) later. Examples include the hard disk, flash drive, memory card and optical (CD/DVD) disk.
(ii) Virtual memory: Virtual memory is a memory-management technique in which a portion of the hard disk (secondary storage) is set aside and used as an extension of the main memory (RAM). When the RAM becomes full, the operating system temporarily moves some data or program pages to this disk area, giving the impression that the computer has more RAM than it physically has. This allows large programs to run even when physical RAM is limited.
(b) Calculations
(i) Number of bits held by each device
Recall: \(1\text{ byte} = 8\text{ bits}\), \(1\text{ KB} = 1024\text{ bytes}\), \(1\text{ MB} = 1024\text{ KB} = 1024 \times 1024\text{ bytes}\).
2 KB:
\[2\text{ KB} = 2 \times 1024\text{ bytes} = 2048\text{ bytes}\]
\[= 2048 \times 8\text{ bits} = 16384\text{ bits}\]
2 MB:
\[2\text{ MB} = 2 \times 1024 \times 1024\text{ bytes} = 2097152\text{ bytes}\]
\[= 2097152 \times 8\text{ bits} = 16777216\text{ bits}\]
(ii) Total capacity of the two devices together, in bytes
\[2\text{ KB} = 2048\text{ bytes}\]
\[2\text{ MB} = 2097152\text{ bytes}\]
\[\text{Total} = 2048 + 2097152 = 2099200\text{ bytes}\]
Question 3 Rapport
(a) (i) identify Figure 1. (ii) Name the parts labeled I, J, K and L in Figure 1
(b)(i) Define the documentation stage in Program Development Life Cycle. (ii) List three characteristics of a good computer program.
(a)(i) Identification of Figure 1
Figure 1 is a flowchart (program flowchart). It is a diagrammatic representation of the sequence of steps and logic used to solve a problem, in which each type of operation is shown by a distinct standard symbol connected by directed flowlines. The diagram begins and ends with an oval (terminal) symbol, which confirms it is a flowchart.
(a)(ii) Names of the labelled parts
| Label | Symbol shape | Name | Function |
|---|---|---|---|
| I | Oval / rounded ellipse | Terminal (Start/Stop) symbol | Marks the beginning (Start) of the program or algorithm. |
| J | Parallelogram | Input/Output (Data) symbol | Represents the entry of data (input) or the display/printing of results (output). |
| K | Diamond / rhombus | Decision (Selection) symbol | Represents a test or condition that has alternative paths, typically a Yes/No or True/False branch. |
| L | Rectangle | Process (Processing) symbol | Represents a processing action such as a calculation or an assignment of a value. |
(The oval at the bottom is again a terminal symbol marking the Stop of the program, and the arrows are the flowlines showing the direction of flow.)
(b)(i) Definition of the documentation stage
The documentation stage of the Program Development Life Cycle is the phase in which all written records, descriptions and instructions concerning the program are prepared and compiled. It produces materials such as the problem definition, algorithm/flowchart, source-code listing with comments, test data and results, and the user manual. Its purpose is to explain how the program was developed and how it is to be used and maintained, so that users can operate it correctly and programmers can understand, correct or modify it later.
(b)(ii) Three characteristics of a good computer program
- Accuracy (correctness): it produces correct and reliable results for all valid inputs.
- Reliability and robustness: it runs without failing and handles invalid or unexpected data gracefully (error handling).
- Readability and maintainability: it is well structured, clearly written and documented so it can be easily understood and modified.
(Other acceptable characteristics include efficiency in use of time and memory, portability, and user-friendliness.)
Détails de la réponse
(a)(i) Identification of Figure 1
Figure 1 is a flowchart (program flowchart). It is a diagrammatic representation of the sequence of steps and logic used to solve a problem, in which each type of operation is shown by a distinct standard symbol connected by directed flowlines. The diagram begins and ends with an oval (terminal) symbol, which confirms it is a flowchart.
(a)(ii) Names of the labelled parts
| Label | Symbol shape | Name | Function |
|---|---|---|---|
| I | Oval / rounded ellipse | Terminal (Start/Stop) symbol | Marks the beginning (Start) of the program or algorithm. |
| J | Parallelogram | Input/Output (Data) symbol | Represents the entry of data (input) or the display/printing of results (output). |
| K | Diamond / rhombus | Decision (Selection) symbol | Represents a test or condition that has alternative paths, typically a Yes/No or True/False branch. |
| L | Rectangle | Process (Processing) symbol | Represents a processing action such as a calculation or an assignment of a value. |
(The oval at the bottom is again a terminal symbol marking the Stop of the program, and the arrows are the flowlines showing the direction of flow.)
(b)(i) Definition of the documentation stage
The documentation stage of the Program Development Life Cycle is the phase in which all written records, descriptions and instructions concerning the program are prepared and compiled. It produces materials such as the problem definition, algorithm/flowchart, source-code listing with comments, test data and results, and the user manual. Its purpose is to explain how the program was developed and how it is to be used and maintained, so that users can operate it correctly and programmers can understand, correct or modify it later.
(b)(ii) Three characteristics of a good computer program
- Accuracy (correctness): it produces correct and reliable results for all valid inputs.
- Reliability and robustness: it runs without failing and handles invalid or unexpected data gracefully (error handling).
- Readability and maintainability: it is well structured, clearly written and documented so it can be easily understood and modified.
(Other acceptable characteristics include efficiency in use of time and memory, portability, and user-friendliness.)
Question 4 Rapport
(a)(i) Define the term encryption. (ii) Tick two authentication techniques involved in security measure from Table 1.
Table 1
| TECHNIQUE | TICK() |
| Firewall | |
| Biometric | |
| Password | |
| Intranet |
(ii) Outline two features of data encryption. (b) While exchanging data with a friend through your mobile phone, you observed that it took a longer time than usual. Outline four factors that may be responsible for the delay in the data transfer.
(a)(i) Encryption is the process of converting readable data (plaintext) into a coded, unreadable form (ciphertext) using an algorithm and a key, so that only an authorised person holding the correct key can decode (decrypt) and read it. Its purpose is to protect the confidentiality of data during storage or transmission.
(a)(ii) Authentication techniques (tick two): Of the four items listed, only Biometric and Password are used to verify a user's identity. A firewall is a network-protection barrier and an intranet is a private network; neither authenticates a user.
| Technique | Tick ( ) |
|---|---|
| Firewall | |
| Biometric | ✓ |
| Password | ✓ |
| Intranet |
(a)(iii) Two features of data encryption:
- It uses a key together with an algorithm to scramble the data, and the same or a matching key is required to reverse it.
- The encrypted output (ciphertext) is unintelligible to anyone who intercepts it without the key, so it preserves confidentiality and integrity of the message.
(b) Four factors that may cause delay in transferring data between mobile phones:
- Weak or unstable network / signal strength between the two devices (poor Bluetooth or Wi-Fi connection).
- Large file size of the data being exchanged, which takes longer to send.
- Low available bandwidth or transfer speed of the connection technology being used.
- Distance or obstacles between the phones, or interference from other electronic/radio devices.
(Other acceptable factors: low battery power forcing power-saving mode, a slow or busy processor, or too many applications running in the background.)
Détails de la réponse
(a)(i) Encryption is the process of converting readable data (plaintext) into a coded, unreadable form (ciphertext) using an algorithm and a key, so that only an authorised person holding the correct key can decode (decrypt) and read it. Its purpose is to protect the confidentiality of data during storage or transmission.
(a)(ii) Authentication techniques (tick two): Of the four items listed, only Biometric and Password are used to verify a user's identity. A firewall is a network-protection barrier and an intranet is a private network; neither authenticates a user.
| Technique | Tick ( ) |
|---|---|
| Firewall | |
| Biometric | ✓ |
| Password | ✓ |
| Intranet |
(a)(iii) Two features of data encryption:
- It uses a key together with an algorithm to scramble the data, and the same or a matching key is required to reverse it.
- The encrypted output (ciphertext) is unintelligible to anyone who intercepts it without the key, so it preserves confidentiality and integrity of the message.
(b) Four factors that may cause delay in transferring data between mobile phones:
- Weak or unstable network / signal strength between the two devices (poor Bluetooth or Wi-Fi connection).
- Large file size of the data being exchanged, which takes longer to send.
- Low available bandwidth or transfer speed of the connection technology being used.
- Distance or obstacles between the phones, or interference from other electronic/radio devices.
(Other acceptable factors: low battery power forcing power-saving mode, a slow or busy processor, or too many applications running in the background.)
Question 5 Rapport
(a) i() What is firewall? (ii) List two methods used in protecting the computer system.
(b) Explain the following stages of the System Development Life Cycle: (i) feasibility study; (ii) design; (iii) maintenance.
(a)(i) What is a firewall?
A firewall is a hardware device, software program, or a combination of both that monitors and controls the flow of data (network traffic) between a computer or private network and an external network such as the Internet. It works by examining incoming and outgoing packets against a set of security rules, allowing safe traffic to pass while blocking unauthorised or malicious traffic. In this way it acts as a protective barrier that prevents intruders and harmful data from reaching the protected system.
(a)(ii) Two methods used in protecting the computer system:
- Installing and updating anti-virus software to detect, quarantine and remove malicious programs.
- Using passwords and user authentication (strong passwords, PINs or biometrics) to restrict access to authorised users only.
Other acceptable methods: using a firewall, regular data backup, encryption of data, keeping the operating system patched/updated, physically securing the hardware.
(b) Stages of the System Development Life Cycle (SDLC):
(i) Feasibility study: This is the early investigation stage that examines whether the proposed system is worth developing. The analyst studies the existing system and assesses the project in terms of technical feasibility (can it be built with available technology?), economic feasibility (do the benefits justify the cost?), and operational feasibility (will users accept and use it?). The result is a feasibility report that recommends whether the project should proceed.
(ii) Design: At this stage the requirements gathered in earlier phases are translated into a detailed plan for the new system. The designer specifies the inputs, outputs, processes, user interfaces (screens and reports), file and database structures, and the hardware and software needed. Both the logical design (what the system will do) and the physical design (how it will be built) are produced as a blueprint for the programmers.
(iii) Maintenance: This is the ongoing stage after the system has been installed and is in use. It involves correcting errors (bugs) discovered during operation, adapting the system to changes in the environment or organisation, and improving or upgrading it to meet new requirements. Maintenance keeps the system accurate, reliable and useful throughout its working life.
Détails de la réponse
(a)(i) What is a firewall?
A firewall is a hardware device, software program, or a combination of both that monitors and controls the flow of data (network traffic) between a computer or private network and an external network such as the Internet. It works by examining incoming and outgoing packets against a set of security rules, allowing safe traffic to pass while blocking unauthorised or malicious traffic. In this way it acts as a protective barrier that prevents intruders and harmful data from reaching the protected system.
(a)(ii) Two methods used in protecting the computer system:
- Installing and updating anti-virus software to detect, quarantine and remove malicious programs.
- Using passwords and user authentication (strong passwords, PINs or biometrics) to restrict access to authorised users only.
Other acceptable methods: using a firewall, regular data backup, encryption of data, keeping the operating system patched/updated, physically securing the hardware.
(b) Stages of the System Development Life Cycle (SDLC):
(i) Feasibility study: This is the early investigation stage that examines whether the proposed system is worth developing. The analyst studies the existing system and assesses the project in terms of technical feasibility (can it be built with available technology?), economic feasibility (do the benefits justify the cost?), and operational feasibility (will users accept and use it?). The result is a feasibility report that recommends whether the project should proceed.
(ii) Design: At this stage the requirements gathered in earlier phases are translated into a detailed plan for the new system. The designer specifies the inputs, outputs, processes, user interfaces (screens and reports), file and database structures, and the hardware and software needed. Both the logical design (what the system will do) and the physical design (how it will be built) are produced as a blueprint for the programmers.
(iii) Maintenance: This is the ongoing stage after the system has been installed and is in use. It involves correcting errors (bugs) discovered during operation, adapting the system to changes in the environment or organisation, and improving or upgrading it to meet new requirements. Maintenance keeps the system accurate, reliable and useful throughout its working life.
