This set of Advanced Microprocessors Questions and Answers focuses on “Protected Virtual Address Mode (PVAM) -2”.
1. Which of the following is a type of system segment descriptor?
a) system descriptor
b) gate descriptor
c) system descriptor and gate descriptor
d) none of the mentioned
View Answer
Explanation: The system segment descriptors are of seven types. The types 1 to 3 are called system descriptors and the types 4 to 7 are called gate descriptors.
2. Which of the following is a type of gate descriptor?
a) call gate
b) task gate
c) interrupt gate
d) all of the mentioned
View Answer
Explanation: The gate descriptors are of four types namely, call gate, task gate, interrupt gate and trap gate.
3. The gate descriptor contains the information of
a) destination of control transfer
b) stack manipulations
c) privilege level
d) all of the mentioned
View Answer
Explanation: The gate descriptor contains the information regarding the destination of control transfer, required stack manipulations, privilege level and its type.
4. The gate that is used to alter the privilege levels is
a) call gate
b) task gate
c) interrupt gate
d) trap gate
View Answer
Explanation: Call gates are used to alter the privilege levels.
5. The gate that is used to specify a corresponding service routine is
a) call gate and trap gate
b) task gate and interrupt gate
c) interrupt gate and trap gate
d) task gate and trap gate
View Answer
Explanation: Interrupt gates and trap gates are used to specify corresponding service routines.
6. The gate that is used to switch from one task to another is
a) trap gate
b) task gate
c) task gate and trap gate
d) none of the mentioned
View Answer
Explanation: Task gate is used to switch from one task to another.
7. The gate that uses word count field is
a) trap gate
b) task gate
c) interrupt gate
d) call gate
View Answer
Explanation: The word count field is only used by a call gate descriptor, to indicate the number of bytes to be transferred from the stack of the calling routine to the stack of the called routine.
8. The memory that maintains the most frequently required data for execution, in a high speed memory is called
a) virtual memory
b) physical memory
c) cache memory
d) ROM (read only memory)
View Answer
Explanation: To minimize the time required for fetching the frequently required descriptor information, from the main memory, cache memory is used in which the most frequently required data for execution is stored.
9. The selector field consists of
a) requested privilege level (RPL)
b) table indicator
c) index
d) all of the mentioned
View Answer
Explanation: In the protected mode, the contents of the segment registers are known as selectors. The selector field consists of three fields namely, RPL, table indicator (TI) and index.
10. If table indicator, TI=0, then the descriptor table selected is
a) local descriptor table
b) global descriptor table
c) local and global descriptor table
d) none of the mentioned
View Answer
Explanation: The type of descriptor table is global if TI=0 and local if TI=1.
11. The instruction that is executed at privilege level zero (0) is
a) LDT
b) LGDT and LLDT
c) GDT
d) None of the mentioned
View Answer
Explanation: The LGDT and LLDT instructions are privileged, and may be executed only at privilege level 0.
12. The instruction that loads a selector which refers to a local descriptor table, containing the base address and limit for LDT is
a) LGT
b) GDT
c) LGDT
d) LLDT
View Answer
Explanation: The LLDT instruction loads a selector, which refers to a local descriptor table, containing the base address, and limit for LDT.
13. The descriptor that is used to store task gates, interrupt gates and trap gates is
a) system descriptor table
b) gate descriptor table
c) interrupt descriptor table
d) none of the mentioned
View Answer
Explanation: The 80286 has a third type of descriptor table known as interrupt descriptor table, which is used to store task gates, interrupt gates and trap gates.
14. The number of interrupt descriptors that the interrupt descriptor table (IDT) handles is
a) 16
b) 64
c) 128
d) 256
View Answer
Explanation: The IDT is able to handle upto 256 interrupt descriptors.
15. The number of bytes required for an interrupt in an IDT is
a) 2
b) 4
c) 6
d) 8
View Answer
Explanation: Six bytes are required for each interrupt in an interrupt descriptor table.
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