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Operating Systemsknowledge~10 mins

System calls and their role in Operating Systems - Interactive Code Practice

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Practice - 5 Tasks
Answer the questions below
1fill in blank
easy

Complete the sentence to explain what a system call is.

Operating Systems
A system call is a [1] that allows a program to request a service from the operating system.
Drag options to blanks, or click blank then click option'
Avariable
Bfunction
Cfile
Drequest
Attempts:
3 left
💡 Hint
Common Mistakes
Confusing system calls with variables or files.
Thinking system calls are just functions within the program.
2fill in blank
medium

Complete the sentence to describe the role of system calls.

Operating Systems
System calls act as a bridge between [1] and the operating system.
Drag options to blanks, or click blank then click option'
Auser programs
Bmemory management
Cnetwork connections
Dhardware devices
Attempts:
3 left
💡 Hint
Common Mistakes
Thinking system calls connect hardware devices directly.
Confusing system calls with network or memory management only.
3fill in blank
hard

Fix the error in the sentence about system calls.

Operating Systems
System calls allow programs to access hardware [1] directly without any restrictions.
Drag options to blanks, or click blank then click option'
Aresources
Bdevices
Cinterfaces
Dmemory
Attempts:
3 left
💡 Hint
Common Mistakes
Assuming system calls give direct hardware access.
Confusing hardware resources with interfaces.
4fill in blank
hard

Fill both blanks to complete the explanation of system call benefits.

Operating Systems
System calls provide [1] to hardware and ensure [2] by managing access.
Drag options to blanks, or click blank then click option'
Acontrolled access
Bfast processing
Csecurity
Ddirect communication
Attempts:
3 left
💡 Hint
Common Mistakes
Choosing 'fast processing' instead of security.
Thinking system calls allow direct communication without control.
5fill in blank
hard

Fill all three blanks to describe how system calls work.

Operating Systems
When a program needs a service, it uses a [1] to send a [2] to the OS, which then [3] the request.
Drag options to blanks, or click blank then click option'
Asystem call
Bsignal
Cprocesses
Dmessage
Attempts:
3 left
💡 Hint
Common Mistakes
Using 'signal' instead of 'message' for communication.
Confusing 'processes' with 'signals' or 'messages'.

Practice

(1/5)
1. What is the main purpose of a system call in an operating system?
easy
A. To write code that runs only on specific hardware
B. To directly access hardware without OS intervention
C. To compile programs into machine code
D. To allow programs to request services from the operating system

Solution

  1. Step 1: Understand what system calls do

    System calls provide a way for programs to ask the operating system to perform tasks on their behalf, such as reading files or managing processes.

  2. Step 2: Compare options with this role

    Only To allow programs to request services from the operating system correctly describes this role. Other options describe unrelated actions like direct hardware access or compilation.

  3. Final Answer:

    To allow programs to request services from the operating system -> Option D

  4. Quick Check:

    System call = request OS service [OK]
Hint: System calls let programs ask OS for help [OK]
Common Mistakes:
  • Thinking system calls bypass the OS
  • Confusing system calls with compiling
  • Assuming system calls are hardware instructions
2. Which of the following is the correct way a program typically uses a system call?
easy
A. By calling a special function provided by the operating system
B. By directly writing machine code instructions
C. By modifying the operating system kernel
D. By sending signals to hardware devices

Solution

  1. Step 1: Identify how programs interact with system calls

    Programs use system calls by calling special functions (APIs) provided by the OS, which then perform the requested service.

  2. Step 2: Eliminate incorrect options

    Direct machine code writing or kernel modification is not how normal programs use system calls. Sending signals to hardware is also not the typical method.

  3. Final Answer:

    By calling a special function provided by the operating system -> Option A

  4. Quick Check:

    System call usage = OS function call [OK]
Hint: System calls are accessed via OS functions, not direct code [OK]
Common Mistakes:
  • Thinking programs write machine code for system calls
  • Believing programs modify the OS kernel directly
  • Confusing hardware signals with system calls
3. Consider this pseudocode using a system call to open a file:
fd = open_file("data.txt")
if fd == -1:
    print("Error opening file")
else:
    print("File opened successfully")

What will be printed if the file does not exist?
medium
A. No output
B. File opened successfully
C. Error opening file
D. System crash

Solution

  1. Step 1: Understand the system call behavior

    The open_file system call returns a file descriptor if successful, or -1 if it fails (e.g., file not found).

  2. Step 2: Follow the conditional logic

    If fd == -1, the program prints "Error opening file". Since the file does not exist, fd will be -1.

  3. Final Answer:

    Error opening file -> Option C

  4. Quick Check:

    File missing -> fd = -1 -> error message [OK]
Hint: Open returns -1 on failure, triggers error print [OK]
Common Mistakes:
  • Assuming file opens successfully even if missing
  • Expecting no output on failure
  • Thinking system calls cause crashes on errors
4. A program tries to read from a file using this code snippet:
bytes_read = read_file(fd, buffer, 100)
if bytes_read == 0:
    print("End of file reached")
elif bytes_read < 0:
    print("Read error")
else:
    print(f"Read {bytes_read} bytes")

But it always prints "Read error" even when the file exists. What is the likely problem?
medium
A. The print statement syntax is incorrect
B. The file descriptor fd is invalid or not opened properly
C. The file is empty
D. The buffer size is too large

Solution

  1. Step 1: Analyze the meaning of bytes_read < 0

    A negative return value from read_file indicates an error, often caused by an invalid file descriptor.

  2. Step 2: Check other options for plausibility

    Buffer size being large or file empty would not cause a read error. Print syntax errors cause compile/runtime errors, not read errors.

  3. Final Answer:

    The file descriptor fd is invalid or not opened properly -> Option B

  4. Quick Check:

    Read error -> invalid fd [OK]
Hint: Negative read means invalid file descriptor [OK]
Common Mistakes:
  • Blaming buffer size for read errors
  • Assuming empty file causes read error
  • Confusing print syntax with read errors
5. You want to write a program that creates a new file, writes data to it, and then closes it using system calls. Which sequence correctly represents these steps?
hard
A. Open file -> Write data -> Close file
B. Write data -> Open file -> Close file
C. Close file -> Open file -> Write data
D. Open file -> Close file -> Write data

Solution

  1. Step 1: Understand the logical order of file operations

    You must first open the file to get a handle, then write data to it, and finally close it to save and release resources.

  2. Step 2: Match the correct sequence

    Only Open file -> Write data -> Close file follows this logical order. Other options have steps in wrong order, which would cause errors or no effect.

  3. Final Answer:

    Open file -> Write data -> Close file -> Option A

  4. Quick Check:

    Open before write, close last [OK]
Hint: Always open before writing, close after done [OK]
Common Mistakes:
  • Trying to write before opening file
  • Closing file before writing
  • Skipping the close step