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a) Virus Detection: Identifies the presence of malware by scanning files and system areas for signatures matching known viruses.

b) Virus Removal: Eliminates the threat after detection by quarantining, repairing, or deleting infected files.

c) Virus Prevention: Proactive measures like real-time monitoring and firewalls to block infections before they occur.

a) External Priority: Specified by the user at the time of initiating the process (e.g., an urgent job).
b) Purchased Priority: Higher priority granted to users who pay a higher rate for faster processing.
c) Internal Priority: Determined by OS scheduling algorithms like Shortest Job First (SJF).
d) Time Slice: A small, fixed interval of time allotted to each process in a multitasking system.

File System: The method used by an OS to organize and track files on a disk.

Tape-based Systems: Sequential access type. Files are stored on physical reels. Simple but inefficient for searching specific data.

Disk-based Systems: Direct access through physical addresses. Divided into tracks and sectors. Uses a device directory for fast retrieval.

Visual Display Unit (VDU): A combination of a Keyboard (input) and Video Screen (output).

a) Dumb Terminal: Responsible only for basic input/output; it has no internal processing power.
b) Intelligent Terminal: Contains its own processor and memory; it can process data locally before sending it to the host.

GUI (Graphical User Interface): A visual way to interact with a computer using symbols like icons, menus, and windows rather than typing text commands. It uses a mouse to navigate, making the computer more user-friendly.

a) Menu Bar: Located at the top of a window; contains pull-down menus for program actions.
b) Title Bar: Displays the name of the program or document and helps identify windows.
c) Scroll Bar: Horizontal or vertical bars used to view information that is currently off-screen.

The three primary process states are:

• Running State: The CPU is currently executing the instructions of the process.
• Ready State: The process is loaded in memory and waiting for its turn to use the CPU.
• Blocked State: The process is waiting for an event (like I/O completion) and cannot proceed.

Security: The ability of an OS to enforce control over data storage and transport.

Elements of Security:

• Confidentiality: Information is not accessed in an unauthorized manner (Read control).
• Integrity: Information is not modified or deleted in an unauthorized manner (Write control).
• Availability: Information is available to authorized users at the right time.

1) Turnaround Time: Total time from job submission to its completion.
2) Waiting Time: Total time a job spends waiting in the ready queue.
3) Terminal Response Time: Time taken for a time-sharing system to respond to a user command.
4) Event Response Time: Time taken for a real-time system to respond to an external event.

1. Virus Detection: Uses checksums to check file integrity or memory-resident monitors to watch for suspicious I/O.
2. Virus Removal: Scans for known bit patterns (signatures) and deletes or repairs the infected code.
3. Virus Prevention: Practices like using legal software, frequent backups, and running real-time monitors.

Computer Virus: A program written to infect other programs; it cannot act independently.

Infection Methods:

• Append: Virus attaches its code to the end of a file.
• Replace: Virus replaces the original program code.
• Insert: Virus injected into the middle of a file.
• Redirect: Changes execution flow to the viral code.

Virtual Memory: A technique that allows the execution of processes that are larger than the physical RAM by using the disk as an extension.

Elements:

• Page Fault: Occurs when a required page is not in RAM, forcing a load from disk.
• Working Set: The collection of pages currently being used by a process in RAM.

System Call: An interface between a program and the OS.
Examples:

• Memory: Allocate/Free memory.
• Process: Read/Block process.
• Information: Create File/Directory.

Multi-user OS: Supports multiple users/processes at the same time (e.g., Mainframes).
Time-sharing OS: Uses CPU scheduling to provide each user a small time slice. The rapid switching makes it appear as if each user has a dedicated CPU.

Information Management (IM): It refers to a set of services that manage the organization, storage, and retrieval of data on various storage devices. It ensures data integrity and controlled access.

System Calls in IM:

• Create(): To create a new file or directory.
• Open(): To open an existing file for reading/writing.
• Read(): To fetch data from a file into a buffer.
• Write(): To transfer data from a buffer to a file.
• Close(): To close an opened file and release resources.

a) Track and Sector: A magnetic disk is divided into concentric circles called Tracks. Each track is further divided into smaller parts called Sectors, which are the basic units of data storage.

b) Seek Time: The time required to move the Read/Write head from its current position to the specific track where data is located.

c) Latency Time: (Also called Rotational Latency) The time taken by the desired sector to rotate and come under the Read/Write head after the head has reached the correct track.

System Call: It is the programmatic way in which a computer program requests a service from the kernel of the operating system.

Usage:

• Application programs (AP) do not have direct access to hardware.
• When an AP needs to perform a task like "Read File" or "Print", it executes a System Call.
• The OS then takes control, performs the privileged task, and returns the result back to the application.