Chapter 6

Question 1

One form of multiprocessing, a situation in which two or more processors operate in unison

Answer 1

parallel processing

Question 2

There are two primary benefits to parallel processing systems: _________________ and ________________.

Answer 2

increased reliability and faster processing

Question 3

Increased flexibility brings increased complexity, however, and two major challenges remain: _________________________

Answer 3

1. how to connect the processors into configurations
2. how to orchestrate their interaction

Question 4

Three typical configurations are:

Answer 4

master/slave configuration
loosely coupled configuration
symmetric configuration

Question 5

a single-processor system with additional slave processors, each of which is managed by the primary master processor

Answer 5

master/slave configuration

Question 6

advantage and disadvantage of master/slave configuration

Answer 6

advantage: simplicity

disadvantage:

• Its reliability is no higher than for a single-processor system because if the master processor fails, the entire system fails.
• It can lead to poor use of resources because if a slave processor should become free while the master processor is busy, the slave must wait until the master becomes free and can assign more work to it.
• It increases the number of interrupts because all slave processors must interrupt the master processor every time they need operating system intervention, such as for I/O requests. This creates long queues at the master processor level when there are many processors and many interrupts.

Question 7

each processor controls its own resources—its own files, access to memory, and its own I/O devices—and that means that each processor maintains its own commands and I/O management tables.

Answer 7

loosely coupled configuration

Question 8

advantage and disadvantage of loosely coupled configuration

Answer 8

advantage: not prone to catastrophic system failures because even when a single processor fails, the others can continue to work independently

disadvantage: difficult to detect when a processor has failed

Question 9

The symmetric configuration has four advantages over loosely coupled configuration:

Answer 9

• It’s more reliable.
• It uses resources effectively.
• It can balance loads well.
• It can degrade gracefully in the event of a failure.

Question 10

disadvantage of symmetric configuration

Answer 10

the most difficult configuration to implement because the processes must be well synchronized to avoid the problems of races and deadlocks

Question 11

other term for symmetric configuration

Answer 11

tightly coupled

Question 12

In a __________________, processor scheduling is decentralized.

Answer 12

symmetric configuration

Question 13

algorithms to resolve conflicts between processors

Answer 13

process synchronization

Question 14

What steps must each processor perform when Processor 1 and Processor 2 finish their current jobs at the same time?

Answer 14

1. Consult the list of jobs to see which one should be run next.
2. Retrieve the job for execution.
3. Increment the READY list to the next job.
4. Execute it.

Question 15

it is a critical section and its execution must be handled as a unit.

Answer 15

critical region

Question 16

explain lock-andkey arrangement

Answer 16

Before a process can work on a critical region, it must get the key. And once it has the key, all other processes are locked out until it finishes, unlocks the entry to the critical region, and returns the key so that another process can get the key and begin work.

Question 17

lock-and-key arrangement consists of two actions

Answer 17

(1) the process must first see if the key is available

(2) if it is available, the process must pick it up and put it in the lock to make it unavailable to all other processes.

Question 18

Several locking mechanisms have been developed, including:

Answer 18

test-and-set
WAIT and SIGNAL
semaphores

Question 19

_______ is a single, indivisible machine instruction known simply as TS and was introduced by IBM for its multiprocessing System 360/370 computers.

Answer 19

Test-and-set

Question 20

two drawbacks of test and set

Answer 20

1. when many processes are waiting to enter a critical region, starvation could occur because the processes gain access in an arbitrary fashion
2. the waiting processes remain in unproductive, resource-consuming wait loops, requiring context switching. (also known as busy waiting)

Question 21

is a modification of test-and-set that’s designed to remove busy waiting.

Answer 21

WAIT and SIGNAL

Question 22

two operations added in WAIT and SIGNAL

Answer 22

WAIT and SIGNAL

Question 23

A _______ is a non-negative integer variable that’s used as a binary signal, a flag.

Answer 23

semaphore

Question 24

In an operating system, a semaphore performs a similar function: It signals if and when a resource is free and can be used by a process. Dijkstra (1965) introduced two operations to overcome the process synchronization problem we’ve discussed. Dijkstra called them P and V, and that’s how they’re known today.

what does P and V stand for

Answer 24

The P stands for the Dutch word proberen (to test)

The V stands for verhogen (to increment).

The P and V operations do just that: They test and increment.

Question 25

The name traditionally given to this semaphore in the literature which is necessary to avoid having two operations attempt to execute at the same time.

Answer 25

mutex, stands for MUTual EXclusion

Question 26

The classic problem of producers and consumers is:

Answer 26

one in which one process produces some data that another process consumes later

Question 27

The classic problem of readers and writers is:

Answer 27

arises when two types of process need to access a shared resource such as a file or database

Question 28

The state of the system can be summarized by four counters initialized to 0:

Answer 28

* Number of readers who have requested a resource and haven’t yet released it (R1 = 0) * Number of readers who are using a resource and haven’t yet released it (R2 = 0) * Number of writers who have requested a resource and haven’t yet released it (W1 = 0) * Number of writers who are using a resource and haven’t yet released it (W2 = 0)

Question 29

Producers and Consumers Algorithm

Answer 29

empty: = n full: = 0 mutex: = 1 COBEGIN repeat until no more data PRODUCER repeat until buffer is empty CONSUMER COEND

Question 30

having a programmer explicitly state which instructions can be executed in parallel

Answer 30

explicit parallelism

Question 31

The automatic detection by the compiler of instructions that can be performed in parallel

Answer 31

implicit parallelism

Question 32

heavyweight processs have the following characteristics:

Answer 32

* They pass through several states from their initial entry into the computer system to their completion: ready, running, waiting, delayed, and blocked. * They require space in main memory where they reside during their execution. * From time to time they require other resources such as data

Question 33

Contents of Thread Control Block

Answer 33

Thread identification Thread state CPU information: Program counter Register contents Thread priority Pointer to process that created this thread Pointers to all other threads created by this thread

Question 34

what 4 cases can concurrent programming be applied?

Answer 34

Case 1: Array Operations Case 2: Matrix Multiplication Case 3: Searching Databases Case 4: Sorting or Merging Files

Question 35

what are the three levels of multiprocessing?

Answer 35

- Job level - Process level - Thread level

Question 36

what kind of arrangement was process synchronization sometimes implemented as?

Answer 36

lock-and-key arrangement

Question 37

these two are implemented using semaphores and both require mutual exclusion and synchronization

Answer 37

producers and consumers readers and writers

Question 38

In the last chapter, we discussed deadlocks. Describe in your own words why mutual exclusion is necessary for multiprogramming systems.

Answer 38

Mutual exclusion is necessary in multiprogramming systems to make sure that only one process uses a shared resource (like a file or printer) at a time. Without it, two or more processes might try to use or change the same resource at once, causing errors, data corruption, or even system crashes. It helps keep processes organized and prevents chaos.

Question 39

There are occasions when several processes work directly together to complete a common task. Two famous examples are the problems of ____________________________. Each case requires both mutual exclusion and synchronization, and each is implemented by using semaphores.

Answer 39

producers and consumers and of readers and writers

Question 40

Order of operations steps:

Answer 40

1. Perform all calculations in parentheses 2. Calculate all exponents 3. Perform all multiplication and division 4. Perform the addition and subtraction For each step, go from left to right.

Question 41

Advantage of test and set

Answer 41

Simple procedure to implement; work well for a small number of processes

Question 42

Three important features of optical disc (chapter 7 ni xD)

Answer 42

Sustained data transfer rate Average access time Cache size

Question 43

Limitations of flash memory

Answer 43

1. The bits can be erased only by applying the flash to a large block of memory 2. With each flash erasure, the block becomes less stable

Question 44

Describe the programmer’s role when implementing explicit parallelism.

Answer 44

They are required to explicitly state which instructions are to be executed in parallel. The programmer is responsible for manually dividing tasks, managing threads or processes, synchronizing data, and ensuring proper communication between them.

Question 45

Describe the programmer’s role when implementing implicit parallelism.

Answer 45

The compiler or system automatically identifies and executes parallel tasks, so the programmer writes normal sequential code without handling parallelization details.