OPERATING SYSTEMS November 2018
Time: 3 hours
THE KENYA NATIONAL EXAMINATIONS COUNCIL
DIPLOMA IN INFORMATION COMMUNICATION TECHNOLOGY
MODULE I
OPERATING SYSTEMS
INSTRUCTIONS TO CANDIDATES:
This paper consists of EIGHT sections. Answer ANY FIVE of the questions in the answer booklet provided. Candidates should answer all questions in English.
1.
a) Explain one function of a memory management unit (MMU).
ANSWER: The Memory Management Unit (MMU) handles the translation of logical memory addresses to physical addresses, ensuring that programs are correctly executed within their allocated memory space.
b) Differentiate between logical and physical memory addresses.
ANSWER: Logical memory addresses are references generated by a program, while physical memory addresses are actual locations in the computer’s hardware memory.
c) A typical operating system is bound to be upgraded over time for a number of reasons. Outline two reasons for this.
ANSWER:
- To patch security vulnerabilities and improve system security.
- To introduce new features and enhancements to improve performance and user experience.
d) John was required to design a file system for a specific application. Outline three factors he should consider when designing the system.
ANSWER:
- Efficiency in storing and retrieving files.
- Data integrity and reliability of file operations.
- Scalability to accommodate future data growth.
2.
a) Outline three process states as used in operating systems.
ANSWER:
- Ready: The process is waiting to be assigned to the CPU for execution.
- Running: The process is currently being executed by the CPU.
- Blocked: The process is waiting for some event (e.g., I/O completion) to proceed.
b) Modern operating systems use various techniques to limit memory wastage. Explain two such techniques.
ANSWER:
- Paging: Dividing memory into fixed-size pages to reduce fragmentation.
- Segmentation: Dividing memory into segments based on the logical divisions of programs.
c) Processors are designed to allow multi-tasking. Outline the factors that the processor must manage in doing so.
ANSWER:
- Allocation of CPU time to multiple tasks (scheduling).
- Efficient context switching between processes.
- Prioritization and handling of interrupts and system calls.
3.
a) Explain four objectives of memory management in an operating system.
ANSWER:
- To provide a convenient abstraction for programming memory.
- To allocate and deallocate memory as needed by processes.
- To protect memory used by one process from being accessed by another.
- To ensure efficient use of the available memory.
b) Differentiate between a CD controller (CTLD) and a Disk Encryption (DE) controller.
ANSWER:
- CD Controller (CTLD): Manages data transfer between a computer and a CD-ROM drive.
- Disk Encryption (DE) Controller: Ensures that the data stored on a disk is encrypted for security purposes.
c) Modern operating systems can use time-based memory prioritizing. Explain two limitations of this memory management technique that can lead to inefficiencies.
ANSWER:
- Overhead in tracking the usage time of memory segments.
- Inaccurate prioritization if memory access patterns change rapidly.
5.
a) List three requirements for a memory management scheme.
ANSWER:
- It must support the protection of processes’ memory spaces.
- It should ensure efficient utilization of memory.
- It must facilitate fast memory allocation and deallocation.
b) Deduce how memory allocation using lists of several continuous blocks could lead to wastage.
ANSWER: Memory allocation using continuous blocks can lead to fragmentation, where small blocks of unused memory are left, making it difficult to allocate large chunks of memory.
c) Distributed Deadlock Detection Algorithms are more commonly used in distributed operating systems. Explain two strengths that could be inherited from centralized approaches.
ANSWER:
- Simplified coordination for detecting and resolving deadlocks.
- Reduced communication overhead between system nodes.
d) An authentication process consists of two steps. Explain these two steps and their importance.
ANSWER:
- Identification: The process of providing credentials (e.g., username).
- Verification: Validating the credentials provided (e.g., password check). Both are critical for ensuring secure access to system resources.
7.
a) Differentiate between access and read-only as used in file operations.
ANSWER:
- Access: Refers to the ability to open or interact with a file.
- Read-only: The ability to view or read a file but not modify its contents.
b) A lecturer described input buffering as done on the OSI model. Outline two techniques used to achieve this and how the second method outshines the first.
ANSWER:
- Single buffering: The system uses a single buffer to hold data before processing.
- Double buffering: Utilizes two buffers to hold data, allowing one to be filled while the other is being processed, thus improving efficiency.
c) Differentiate between Aaron and machine I/O operations.
ANSWER: Aaron I/O is theoretical and does not exist in standard terminology. Machine I/O refers to input/output operations directly handled by the hardware.
8.
a) Define the term I/O and its relevance in operating systems.
ANSWER:
- I/O (Input/Output): Refers to the communication between a computer system and external devices, such as keyboards, screens, and storage devices. It is essential for interacting with hardware components and performing tasks like reading or writing data.
b) There are several file descriptors systems that do not support simple file operations. Outline three examples of these file operations.
ANSWER:
- Seek: Moving the read/write pointer within a file.
- Open: Accessing a file for reading or writing.
- Close: Terminating the connection to a file after an operation is completed