Question 1
Which of the following statements about synchronous and asynchronous I/O is NOT true?
An ISR is invoked on completion of I/O in synchronous I/O but not in asynchronous I/O
In both synchronous and asynchronous I/O, an ISR (Interrupt Service Routine) is invoked after completion of the I/O
A process making a synchronous I/O call waits until I/O is complete, but a process making an asynchronous I/O call does not wait for completion of the I/O
In the case of synchronous I/O, the process waiting for the completion of I/O is woken up by the ISR that is invoked after the completion of I/O
       Operating-Systems       I/O-Handling       Gate-2008
Question 1 Explanation: 
Synchronous I/O mean that some flow of execution (such as a process or thread) is waiting for the operation to complete. Asynchronous I/O means that nothing is waiting for the operation to complete and the completion of the operation itself causes something to happen.
Synchronous I/O -- some execution vehicle (like a process or thread) that initiates the I/O also waits for the I/O to complete (and perhaps completes it). When the I/O completes, that same execution vehicle goes on to do something else, perhaps using the results of the I/O.
Asynchronous I/O -- no execution vehicle waits for the I/O to complete. When the I/O completes, whatever execution vehicle happens to complete the I/O may arrange for later things to happen.
Option B is not true, because both synchronous and asynchronous I/O, an ISR (Interrupt Service Routine) is not invoked after completion of the I/O.
Question 2

Normally user programs are prevented from handling I/O directly by I/O instructions in them. For CPUs having explicit I/O instructions, such I/O protection is ensured by having the I/O instructions privileged. In a CPU with memory mapped I/O, there is no explicit I/O instruction. Which one of the following is true for a CPU with memory mapped I/O?

I/O protection is ensured by operating system routine(s)
I/O protection is ensured by a hardware trap
I/O protection is ensured during system configuration
I/O protection is not possible
       Operating-Systems       I/O-Handling       Gate-2005
Question 2 Explanation: 
I/O protection can be ensured by operating system. Because all the user application are not modified by user mode. Those are sent to kernal mode as a system calls.
Question 3

What is the bit rate of a video terminal unit with 80 characters/line, 8 bits/character and horizontal sweep time of lOOµs (including 20 µs of retrace time)?

8 Mbps
6.4 Mbps
0.8 Mbps
0.64 Mbps
       Operating-Systems       I/O-Handling       Gate 2004-IT
Question 3 Explanation: 
Horizontal sweep time = 100µs
Total number of bits transmitted = 80 * 8 = 640 bits
Bit rate = (640 * 106)/100 = 6.4 Mbps
Question 4
Data transfer between a microprocessor and an I/O device is usually faster in memory-mapped-I/O scheme than in I/O-mapped - I/O scheme.  
       Computer-Organization       I/O-Handling       GATE-1987
Question 4 Explanation: 
Memory mapped I/0 runs faster than I/0 mapped I/O.
There are 4 questions to complete.
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