Take This CompTIA A+ Essentials Quiz On IRQ Assignments!

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Questions: 14 | Attempts: 1,855 | Updated: Mar 19, 2023

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This CompTIA A+ Essentials quiz has been made to see whether you are completely prepared for the real exam. This practice test will help you pass by familiarizing you with the material and the ensuring that you know the structure. This quiz has been made to test your knowledge about the IRQ(Interrupt Request Line)
assignments in modern PCs. Read the questions carefully and answer. So, let's try out this quiz. Good Luck!

Questions and Answers

1.

Which IRQ is assigned to the system timer?
- A.
  
  IRQ 1
- B.
  
  IRQ 7
- C.
  
  IRQ 8
- D.
  
  IRQ 0
Correct Answer
D. IRQ 0

Explanation
IRQ 0 is used for the system timer. IRQ 8 is the Real-Time Clock.

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2.

What IRQ is used by the keyboard?
- A.
  
  IRQ 2
- B.
  
  IRQ 3
- C.
  
  IRQ 1
- D.
  
  IRQ 6
Correct Answer
C. IRQ 1

Explanation
The correct answer is IRQ 1. The keyboard uses IRQ 1 as its interrupt request line. IRQ stands for Interrupt Request and it is a signal sent to the processor to request attention or to interrupt its current operation. The keyboard sends an interrupt signal to the processor when a key is pressed, and this signal is assigned to IRQ 1.

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3.

Which IRQ is used to "cascade" higher-numbered interrupt requests to the higher-priority IRQ 2?
- A.
  
  IRQ 9
- B.
  
  IRQ 8
- C.
  
  IRQ 10
- D.
  
  IRQ 7
Correct Answer
A. IRQ 9

Explanation
Early in PC development, only IRQs 0-7 existed; lower numbers were assigned higher priority. When additional IRQs were needed, IRQ 2 was modified to accept signals from IRQs 8-15, to allow higher-numbered IRQs to obtain a higher priority.

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4.

Which IRQ is assigned to COM2/COM4?
- A.
  
  IRQ 4
- B.
  
  IRQ 3
- C.
  
  IRQ 5
- D.
  
  IRQ 1
Correct Answer
B. IRQ 3

Explanation
Com (usually serial) ports 2 and 4 use IRQ 3. IRQ 4 is used by the other two (COM1/COM3).

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5.

IRQ 4 is used by what device?
- A.
  
  COM2/COM4
- B.
  
  COM1/COM3
- C.
  
  LPT1
- D.
  
  No specific device is assigned; this IRQ handles cascaded signals from IRQs 8-15.
Correct Answer
B. COM1/COM3

Explanation
Com ports 1 and 3 use IRQ 4. COM2/COM4 use IRQ 3, the lower-numbered (and higher priority) interrupt request.

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6.

IRQ 5 is used by what device?
- A.
  
  COM1/COM3
- B.
  
  Primary IDE controller
- C.
  
  LPT1
- D.
  
  LPT2
Correct Answer
D. LPT2

Explanation
IRQ 5 is used by the LPT2 device. IRQ stands for Interrupt Request and it is used by devices to request the attention of the CPU. LPT2 refers to the second parallel port on a computer, which is used for connecting printers and other parallel devices. Therefore, the correct answer is LPT2 as it correctly identifies the device that uses IRQ 5.

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7.

Which IRQ is assigned to the floppy disk controller?
- A.
  
  IRQ 8
- B.
  
  IRQ 6
- C.
  
  IRQ 4
- D.
  
  IRQ 2
Correct Answer
B. IRQ 6

Explanation
The correct answer is IRQ 6. IRQ stands for Interrupt Request and it is a signal sent by a hardware device to the CPU to request attention. In the case of the floppy disk controller, it is assigned IRQ 6. This means that when the floppy disk controller needs to communicate with the CPU, it will send an interrupt request on IRQ 6.

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8.

Choose which IRQs are assigned to printer (LPT) ports:
- A.
  
  IRQ 1
- B.
  
  IRQ4
- C.
  
  IRQ 7
- D.
  
  IRQ 6
- E.
  
  IRQ 5
Correct Answer(s)
C. IRQ 7
E. IRQ 5

Explanation
The IRQs assigned to printer (LPT) ports are IRQ 7 and IRQ 5. These IRQs are commonly used for parallel ports, such as printer ports. IRQ 7 is typically used for the first parallel port (LPT1) and IRQ 5 is used for the second parallel port (LPT2). These IRQs are responsible for managing the communication between the printer and the computer, allowing data to be sent and received effectively.

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9.

IRQ 8 is used by what device?
- A.
  
  Real-time clock
- B.
  
  Secondary IDE controller
- C.
  
  Primary IDE controller
- D.
  
  System timer
Correct Answer
A. Real-time clock

Explanation
IRQ 8 is used by the real-time clock. The real-time clock is responsible for keeping track of the current time and date in a computer system. It is an essential component for various time-sensitive operations and functions. By utilizing IRQ 8, the real-time clock can interrupt the processor when it needs to update or synchronize the system time. This ensures accurate timekeeping and synchronization with other devices in the computer system.

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10.

Which IRQs are system-reserved and cannot be reassigned?
- A.
  
  IRQ 2
- B.
  
  IRQ 9
- C.
  
  IRQ 0
- D.
  
  IRQ 1
- E.
  
  IRQ 8
Correct Answer(s)
C. IRQ 0
D. IRQ 1

Explanation
The only IRQs that are actually reserved by the system are IRQ 0 (System timer) and IRQ 1 (keyboard). IRQ 2 "cascades" with IRQ 9, such that the system will see these as the same assignment; they are not, however, technically "reserved". IRQ 8 is used for the Real-Time Clock, but is not reserved either.

It is worth noting that IRQ 1 is always reserved for a keyboard, even if no keyboard is present or needed.

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11.

Which IRQs are typically free, by default, assuming all other default assignments are taken?
- A.
  
  IRQ 12
- B.
  
  IRQ 11
- C.
  
  IRQ 10
- D.
  
  IRQ 13
- E.
  
  IRQ 9
Correct Answer(s)
B. IRQ 11
C. IRQ 10
E. IRQ 9

Explanation
IRQ 9 is free, despite being "cascaded" to IRQ 2; it has no default assignment. IRQs 10 and 11 have no default assignment or other role at all.

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12.

Which device is typically assigned to IRQ 12?
- A.
  
  None; it is free, by default
- B.
  
  PS/2 mouse
- C.
  
  Primary IDE controller
- D.
  
  Keyboard
Correct Answer
B. PS/2 mouse

Explanation
Although IRQ 12 can be free if no PS/2 mouse is present, it is in use, by default, when a standard mouse is attached. USB mice do not occupy this interrupt, if installed.

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13.

Which device uses IRQ 13?
- A.
  
  Video interrupt handler
- B.
  
  Keyboard
- C.
  
  Math coprocessor
- D.
  
  Primary IDE controller
Correct Answer
C. Math coprocessor

Explanation
While IRQ 13 was used on legacy systems to control portions of the ISA bus, it is now used by the math coprocessor integrated into all modern CPUs.

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14.

Which IRQ is assigned to the secondary IDE controller?
- A.
  
  IRQ 17
- B.
  
  IRQ 16
- C.
  
  IRQ 15
- D.
  
  IRQ 14
Correct Answer
C. IRQ 15

Explanation
The correct answer is IRQ 15. IRQ stands for Interrupt Request and it is a signal sent to the processor to inform it that a device needs attention. The secondary IDE controller is responsible for connecting secondary IDE devices such as CD/DVD drives or additional hard drives. IRQ 15 is commonly assigned to the secondary IDE controller in order to enable communication between the controller and the processor.

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Take This CompTIA A+ Essentials Quiz On IRQ Assignments!

Which IRQ is assigned to the system timer?

What IRQ is used by the keyboard?

Which IRQ is used to "cascade" higher-numbered interrupt requests to the higher-priority IRQ 2?

Which IRQ is assigned to COM2/COM4?

IRQ 4 is used by what device?

IRQ 5 is used by what device?

Which IRQ is assigned to the floppy disk controller?

Choose which IRQs are assigned to printer (LPT) ports:

IRQ 8 is used by what device?

Which IRQs are system-reserved and cannot be reassigned?

Which IRQs are typically free, by default, assuming all other default assignments are taken?

Which device is typically assigned to IRQ 12?

Which device uses IRQ 13?

Which IRQ is assigned to the secondary IDE controller?