Os Sistemas Operacionais

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- Astonishment Factor

A characteristic of some user interface elements that causes the user to be “astonished” when the interface does something unexpected. One cause of this might be automatic command completion.

- Interrupt Vector

A storage location in the low addresses of memory used to contain information such as a handler address used to process a particular type of interrupt.

- Interrupt Vector

A small block of memory, usually at the lowest addresses, dedicated to handling a particular interrupt. The interrupt vector specifies where the handler is located and may provide storage for saving critical state information.

- Dispatcher

A component of a short term scheduler that is responsible solely for selecting the next process to run when the processor is free and performing the context switch. The process chosen is always the highest priority process that is in the ready state.

- Physical resource

A resource consisting of a physical object such as memory or the processor.

- Logical resource

A resource that does not correspond directly to a physical object. Examples include files, processes, messages, etc.

- Job Control Language

A language used to specify instructions to the OS for processing a batch job. The JCL was an early type of user interface.

- Fork and Exec

The two operations used to create a new process in Unix or Unix-based systems. Fork creates a clone of the original process, running the same code. Exec then optionally overlays one of the clones with a new program.

- Feedback queues

A system of scheduling queues for processes in the READY state in an interactive timesharing system. Processes becoming ready are placed in the highest priority queue and given a short time quantum. If they complete quickly, they are considered interactive and will return to high priority. If they compute for a long time, they will migrate to lower priority queues with longer time quanta.

- Re-entrant procedure

A procedure that is designed in such a manner that it may be interrupted by a call to another instance of itself without incorrect behavior. Such a procedure must operate on private variables and parameters only, and may not access global variables or cause side effects.

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(10 points)

An operating system is a manger of resources. Identify the two principal objectives of resource management, and give a brief example for each objective.

- Convenient use. An example is a file system, which makes it much more convenient to manage information on a storage device.

- Controlled sharing. An example is a device allocation routine, which ensures that only one process at a time is permitted to use a particular device.

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(10 points)

Match an OS from the list given to each of the descriptive phrases below. You may use the same name more than once. Here is the list:

SOS, SAGE, SABRE, ATLAS, OS/360, VMS, CTSS, MULTICS, T.H.E., UNIX, CP/M, SHARE OS, CTSS, , MS-DOS, WINDOWS

- Designed by IBM users = SOS

- Introduced the interrupt concept = ATLAS

First system to provide virtual memory = ATLAS

First OS with virtual memory = ATLAS

- The principal influence for the design of Unix = MULTICS

Principal influence on design of Unix = MULTICS

A highly secure OS = MULTICS

- The first popular OS for microcomputers = CP/M

- The first timesharing system = CTSS

- An OS written by a users group = SHARE OS

- Splits process creation into fork and exec operations = UNIX

- Principal influence on design of Windows NT = VMS

- First real-time operating system = SAGE

- Its design was greatly influenced by VMS = WINDOWS

- A huge OS delivered very late and full of bugs = OS/360

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(15 points: 5 each)

These questions concern the design of a user interface.

- Identify two tasks normally performed by a terminal handler.

Some examples, as found in the text, include echoing, line buffering, handling break characters, etc. A brief phrase is sufficient.

- A common way to confirm a “dangerous” action, such as deleting all files in a directory, is to ask a question such as “ARE YOU SURE (Y OR N)?” Explain a problem with this type of confirmation.

The biggest danger with this method is that users will grow overly used to it and type Y without thinking. If the action is truly drastic, it would be better to use a confirmation method that forces the user to stop and think for a moment.

- In spite of the popularity and attractiveness of Graphic User Interfaces (GUIs), Command Line Interfaces (CLIs) are often used. Give one reason for this.

- When communicating with a remote server, the CLI greatly reduces communication costs

- Scripting is easier

- More complex parameters and options can be specified simply

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(10 points)

Name each of the three levels of process scheduling, and identify the resource or resources scheduled by each level.

- High-level or long-term: