1930/316
OPERATING SYSTEMS
July 2015
Time: 3 hours
THE KENYA NATIONAL EXAMINATIONS COUNCIL
CRAFT CERTIFICATE IN INFORMATION TECHNOLOGY
MODULE I
OPERATING SYSTEMS
3 hours
INSTRUCTIONS TO CANDIDATES
This paper consists of TWO sections: A and B.
Answer all the questions in section A and any TWO questions from section B in the answer booklet provided.
Candidates should answer the questions in English.
SECTION A (40 marks)
Answer ALL the questions in this section.
Outline four features of a real-time operating system.
Deterministic response times.
Multi-tasking capabilities.
Priority scheduling.
Minimal latency.
Tom uses sequential method to organize files in his computer. Outline four challenges he is likely to encounter.
Difficulty in file retrieval.
Increased time to access specific files.
Inefficient space utilization.
Complexity in managing large numbers of files.
Sarah installed drivers for new computer hardware. Explain two reasons for this installation.
Ensures compatibility between hardware and the operating system.
Allows the operating system to communicate with the hardware effectively.
Explain two circumstances that could lead to the use of the long-term scheduler in a computer system.
When the system is under heavy load and needs to control the degree of multiprogramming.
When deciding which jobs should be admitted to the ready queue based on available system resources.
Explain each of the following terms as used in operating systems:
(i) Kernel
The core part of an operating system that manages system resources and communication between hardware and software.
(ii) Interrupt
A signal to the processor indicating that an event needs immediate attention, pausing the current processes to handle the event.
A computer system uses dynamic partitioning in its memory management. Explain two advantages of this type of partitioning.
Reduces memory wastage as partitions can adjust to the size of the process.
Improves system efficiency by allowing multiple processes to occupy memory simultaneously.
Outline four challenges of the First-Come First-Served (FCFS) process scheduling algorithm.
Long average waiting time.
Convoy effect where short processes wait behind long ones.
Poor response time for interactive users.
No prioritization, leading to inefficiency in process handling.
Differentiate between CLOOK and C-SCAN disk scheduling algorithms.
CLOOK: The disk arm moves only as far as the last request in one direction and then jumps back to the beginning of the queue.
C-SCAN: The disk arm moves in one direction, servicing requests, and then returns to the beginning without servicing any requests on the way back.
Explain each of the following terms as used in file protection:
(i) Access control
Mechanisms that restrict access to files based on user permissions.
(ii) Audit trail
A record that shows who accessed a file and what operations were performed.
Jane installed an operating system software in a new computer. Outline four advantages of this software.
Provides a user interface for interaction with the computer.
Manages hardware resources efficiently.
Enables the execution of application programs.
Offers security features to protect system data.
SECTION B (60 marks)
Answer any TWO questions from this section.
(a) Outline four advantages of paging as used in memory management.
Eliminates the need for contiguous allocation of physical memory.
Reduces external fragmentation.
Simplifies the management of memory by the operating system.
Allows for efficient use of available memory.
(b) A computer system uses linked file allocation technique. Explain three limitations of this technique.
Slower access time due to the need to traverse the file links.
Difficulty in direct access as each block must be read sequentially.
Increased chance of losing file data if one block’s link is corrupted.
(c) With the aid of a diagram, describe the three types of user accounts.
Administrator: Full control over the system, including system settings and user management.
Standard User: Limited access with permission to use installed applications and files.
Guest User: Minimal access, typically used for temporary users with no personalization.
(a) Outline three components of a hard disk drive.
Platter: The magnetic surface where data is stored.
Read/Write Head: The component that reads data from or writes data to the platter.
Spindle: The axis that rotates the platters.
(b) Caroline requests two processors in her office (core 2 duo, 2048KB, 500GB, 2048KB and core 2 quad, 4096KB, 1000GB, 4096KB). Explain how the two processors are allocated to the available memory using each of the following partition allocation methods:
(i) Best fit
Allocates the smallest partition that can accommodate the requested memory, minimizing wasted space.
(ii) First fit
Allocates the first available partition that is large enough to accommodate the requested memory.
(c) A memory access time of a hard disk is 5ms. Explain three factors that would determine the hard disk access time.
Seek time: The time taken for the read/write head to move to the correct track.
Rotational latency: The delay waiting for the disk platter to rotate to the correct sector.
Data transfer rate: The speed at which data is read from or written to the disk.
(a) Define the term batch format as used in operating systems.
A method where jobs are collected into a batch and processed without user interaction.
(b) Outline three characteristics of a good scheduling algorithm.
Fairness in allocating resources to processes.
Efficiency in resource utilization.
Predictability in the order and timing of process execution.
(c) Explain two circumstances when batch operating systems would be appropriate.
When processing large volumes of data without the need for immediate output.
In environments where similar jobs are processed repeatedly, reducing the need for user interaction.
(d) A technical institute uses client/server operating system model.
(i) With the aid of diagrams, describe this structure.
A client/server model involves clients requesting services from a central server, which processes the requests and sends back responses.
[Diagram would depict clients connected to a central server.]
(ii) Outline two advantages of this model.
Centralized management of resources and data.
Easier to maintain and update software on the server.
(a) Explain each of the following directory structures:
(i) Single level
All files are stored in a single directory, making organization simple but difficult to manage as the number of files grows.
(ii) Tree
Files are organized in a hierarchy with directories and subdirectories, allowing for better organization and easier navigation.
(b) Differentiate between cooperative and priority scheduling algorithms.
Cooperative Scheduling: Processes voluntarily yield control to allow other processes to run.
Priority Scheduling: Processes are assigned a priority, and the scheduler selects the process with the highest priority to run next.
(c) A virus has infected the partition part of a computer system. Describe two functions of this section.
Partition Table Management: Manages the division of a disk into partitions, each of which can be treated as a separate disk.
Boot Management: Stores boot loader code and information necessary to start the operating system.
(d) A technician detected a deadlock in a computer during troubleshooting. Outline three measures that could be used to recover from this deadlock.
Process Termination: Killing one or more processes involved in the deadlock.
Resource Preemption: Forcibly taking resources from some processes and reallocating them.
Rollback: Reverting processes to an earlier safe state.
(a) Alice created a zip file in her computer system. Outline four attributes that this file could possess.
File Size: The compressed size of the zip file.
File Name: The name of the zip file.
Compression Method: The algorithm used to compress the contents.
File Path: The directory location where the zip file is stored.
(b) Explain two functions of a shell component in a computer system.
Command Interpretation: Takes user input as commands and interprets them for execution by the operating system.
Script Execution: Allows the execution of sequences of commands (scripts) to automate tasks.