CPSC 100, Fall 1997:
Answers to Quiz #5

This is the fifth quiz from the course Computer Science 100: Principles of Computer Science, taught by David Eck. The answers that are included here are sample answers only. There might be many other answers to a given problem that would also receive full credit. See the home page for the text, The Most Complex Machine, for more information about the course.

Question 1: What is an operating system? What are some of the things that an operating system does?

Answer: The operating system is the software that is required for the basic operation of a computer. It is considered part of the system itself, and not an add-on like an application program. It includes the device drivers that the CPU uses to communicate with and control other devices. It provides subroutines for performing common tasks; these subroutines are available to be called by application programs. It controls allocation of space in memory and on disk drives. It starts up other programs, and in the case of a multitasking system, it is responsible for switching from one program to another. (Some people include the user interface as part of the operating system, but others consider the interface to be a specialized application program.)

Question 2: An expansion slot can be used to add a new hardware device to a computer system. Explain what this means, how it works, and what it has to do with the system bus.

Answer: The bus is a set of wires that connects the CPU to other devices, so that the CPU can communicate with those devices and control them. An expansion slot provides a way for a new device to be "plugged into" the bus. In this way, any device that is designed to be plugged into the expansion slot can be added to the system. The system does not have to be explicitly designed to support that device. (Of course, besides plugging the device physically into the system, you probably have to add a device driver to the operating system. Otherwise, the CPU won't know how to communicate with the device.)

Question 3: Briefly explain the startup process that a computer goes through when it is first turned on. Why is a "startup process" necessary in the first place?

Answer: When a computer is turned off, most of its memory (the "dynamic RAM") is erased. However, part of the memory consists of ROM (read-only memory), which stores information permanently, even when the power is off. The ROM contains a simple "boot" program that begins the process of rebuilding the contents of the memory and configuring all the hardware devices. At the end of the process, device drivers have been loaded, the operating system is running, and the whole system is ready to be used.

Question 4: Interrupts are one method of communication between the CPU and other devices. Give at least two examples of how interrupts might be used. (What device sends the interrupt? Why? What kind of information is sent?)

Answer: For example:

Question 5: Define the term microprocessor.

Answer: A microprocessor is a complete CPU on a single integrated circuit chip.

David Eck, 27 October 1997