The writing Module. VII. Reading Exercises:

THE SPEAKING MODULE

After text activity

VII. Reading Exercises:

Exercise 1. Read and memorize using a dictionary:

Currently, accountable for, confusion, extra piece of hardware, impenetrable, contents, executing program, integrity, responsible, to perform, to load, requester

Exercise 2. Answer the questions:

1) What might one expect the supervisor program to maintain?

2) What does virtual processor implementation contain?

3) What protection mechanisms are described in the text?

4) What does each mechanism protect?

5) What program is part of all three protection mechanisms?

Exercise 4. Match the left part with the right:

1 So far, this virtual processor implementation contains	a) three protection mechanisms that we can associate with our abstractions.
2. For the first, the information being protected is the	b) forces all references to memory through the descriptor mechanism.
3. The guard is represented by the extra	c) distinct programs of Fig. 1.
4. The impenetrable wall with a door is the hardware that	d) piece of hardware that enforces the descriptor restriction.

II. Speaking Exercises:

Exercise 1. Define the terms using the suggested words and expressionsas in example:

Information science	Descriptor	Code	Binary code
discipline, deals with, processes, storing, transferring, information	piece stored data indicates how data stored	system, symbols, rules, used, expressing, information	code, digital, computers, based, binary, number, system, there are, two, possible, states, off and on, usually, symbolized, 0 and 1

EXAMPLE: Information science is a discipline that deals with the processes of storing and transferring information.

Exercise 2. Ask questions to the given answers:

1) Question: ___________________________________________?

Answer: When the privileged state bit is OFF, the index in this table of the program currently in control identifies exactly which program--and thus which virtual processor--is accountable for the activity of the real processor.

2) Question: ___________________________________________?

Answer: For protection to be complete, a virtual processor must not be able to change arbitrarily the values in the table of descriptors.

3) Question: ___________________________________________?

Answer: If we suppose the table to be stored inside the supervisor program, it will be inaccessible to the virtual processors.

Writing exercises:

Exercise 1. Fill in the gaps with the suggested words:

requester, not, first, identified, mechanism

The second ________protects the contents of the descriptor register. The wall, door, and guard are implemented in hardware, as with the ______mechanism. An executing program requesting to load the descriptor register is__________ by the privileged state bit. If this bit is OFF, indicating that the requester is a user program, then the guard does ______allow the register to be loaded. If this bit is ON, indicating that the______ is the supervisor program, then the guard does allow it.

Exercise 2. Compose a story on one of the topics (up to 100 words):

1) Different protection mechanisms

2) Authority check

Lesson 8

Дата добавления: 2015-08-31