Os Sistemas Operacionais

1. (20 points: 2 each)

TRUE OR FALSE

1. UNIX was originally designed as a single-user OS  TRUE 
2. OS/360 was delivered on time and with few bugs. FALSE

OS/360 was years late and hundreds of bugs were found.

1. Timesharing was not feasible before the development of file systems. TRUE 
2. A user interface interacts with the OS though the program interface. TRUE
3. Command languages do not provide conditional and loop structures, since they would have no use. FALSE

These structures are important in scripts and CLI programs

1. A system call is often implemented as a type of interrupt. TRUE 
2. Some OSs provide ID numbers for processes, but every system requires processes to have names. FALSE

Process IDs are always used.  Names are optional.

1. A process must always be in the ready state before changing to the running state. TRUE 
2. A drawback of shortest-job-first scheduling is that it may make long jobs wait forever. TRUE 
3. When scheduling with feedback queues, highly interactive processes should be assigned high priorities and short time quanta. TRUE 
4. A file is an example of a physical resource. FALSE 
5. Windows system administrators generally can do everything they need to do using the graphic user interface only. FALSE
6. Timesharing was not feasible before the development of file systems. TRUE 
7. A process must always be in the ready state before changing to the running state. TRUE
8. First-Come, First-Served scheduling provides the shortest average waiting time. FALSE
9. In a typical computing system disk interrupts occur more often than any other type. FALSE
10. Some OSs provide ID numbers for processes, but every system requires processes to have names. FALSE 
11. One important responsibility of a system call instruction is to put the hardware in privileged mode. TRUE
12. MS-DOS was written from scratch by Bill Gates.
13. If an OS supports virtual timers, the number of virtual timers equals the number of physical clocks. FALSE 
14. A file is an example of a physical resource. FALSE 

A file is a logical resource.

1. The first operating systems were developed in the 1950s. TRUE
2. MS-DOS was written from scratch by Bill Gates. FALSE

Gates purchased the OS from Seattle Computer Products.

1. OS/360 was delivered on time and with few bugs. FALSE
2. Shortest job first scheduling provides the shortest possible average waiting times. TRUE
3. When a running process makes a request for resources, it is placed in the suspended state. FALSE

The process is initially placed in the blocked state.

1. In an interactive system, if context switching had no cost, it would be desirable to switch running processes infinitely often. TRUE 
2. When scheduling interactive processes using feedback queues, a process doing a long computation will be given a low priority and a short time quantum. FALSE 

High priority, short TQ.

1. In all OSs in common use today, processes have character string names. FALSE
2. In a typical computing system disk interrupts occur more often than any other type. FALSE

Timer interrupts are the most frequent.

1. (20 points: 4 each)

Explain briefly each of the following terms.

1. Logical resource

A resource that is information rather than a physical object.  Examples are files, data structures, processes.

1. Keyword arguments

Command Language arguments that are identified by a string name, for example, SOURCE=FILE1.  Contrasts with positional arguments.

1. Aging

 A technique used to avoid starvation of low-priority processes in a priority-based scheduler.  Periodically the priority of all processes in the queue is raised.  Eventually the long-waiting processes will have a high enough priority to be scheduled.

1. Aging

A strategy for avoiding “starvation” (indefinite delay of low-priority processes) in a priority-based scheduler such as SJF.  Periodically, the priority of all processes is raised.  Eventually, long-waiting processes will have their priority raised enough that they will be scheduled.

1. 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.

1. 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.

1. 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.

1. 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.

1. Physical resource

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

1. Logical resource

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

1. 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.