Operating Systems Final Exam Ch. 5,6,7,8

Search strategy

A search strategy is an organised structure of key terms used to search a database. The search strategy combines the key concepts of your search question in order to retrieve accurate results.

directories

Also referred to as folders; they are used for organizing and storing computer files.

Physical storage allocation

Contiguous Storage. One of the ways data is saved on the disk is through contiguous storage or allocation. In this method, files are saved next to each other in available continuous spaces or data blocks.

Avoidance

Deadlock avoidance algorithms try not to allocate resources to a process if it will make the system in an unsafe state. ... An edge from a process to resource is a request edge and an edge from a resource to process is an allocation edge.

WAIT and SIGNAL

System calls to the OS

LOOK

The LOOK algorithm is the same as the SCAN algorithm in that it also honors requests on both sweep direction of the disk head, however, this algorithm "Looks" ahead to see if there are any requests pending in the direction of head movement.

Volume

The amount of space an object takes up

I/O Subsystem

a collection of modules within the operating system that controls all I/O requests.

Database File

collection of related records

Inter-block gap (IBG)

the area or space separating consecutive blocks of data or consecutive physical records on an external storage medium.

Sequential record organization

the organization of records in a specific sequence. Records in a sequential file must be processed one after another.

Parallel processing

the processing of program instructions by dividing them among multiple processors with the objective of running a program in less time. ... An early form of parallel processing allowed the interleaved execution of both programs together.

Symmetric

the processing of programs by multiple processors that share a common operating system and memory. In symmetric (or "tightly coupled") multiprocessing, the processors share memory and the I/O bus or data path. A single copy of the operating system is in charge of all the processors.

Transfer time

the time for the entire sector to pass under the read/write head and have its contents read into or written from memory.

____ semaphores are used in the producer and consumer problem.

three

Deadlock is a system-wide tangle of resource requests that begins when two or more jobs are put on hold, each waiting for a vital resource to become available.

true

The common element in all synchronization schemes is to allow a process to finish work on a critical region of the program before other processes have access to it.

true

When multiprocessing takes place at the thread level, a high degree of synchronization is required to disassemble each process.

true

Master file directory

used to keep track of each users directory, and must be maintained when users are added to or removed from the system. A separate directory is generally needed for system ( executable ) files.

RAID

usually refers to a redundant array of independent disks. RAID storage uses multiple disks in order to provide fault tolerance, to improve overall performance, and to increase storage capacity in a system.

V(s) increment -signal

: Increments the value of semaphore variable by 1. After the increment, if the pre-increment value was negative (meaning there are processes waiting for a resource), it transfers a blocked process from the semaphore's waiting queue to the ready queue.

record

A collection of fields that appear as a row in a database or table.

file

A collection of related data stored on a lasting medium, such as a hard disk.

Concurrent Programming

A concurrent program has multiple threads of control. They may be executed as parallel processes. In all these cases, the basic principles of concurrent programming are the same. Operating System usually provides a logical abstraction for the underlying hardware, and concurrent programs are based on such abstractions.

Fixed-head

A direct access storage device, such as a disk or drum, that has a read/write head for each track. Since there is no access arm movement, access times are significantly improved.

process cooperation

A process is independent if it cannot affect other other process or be affected by it. Any process that does not share data with others is independent. Otherwise the process is cooperating. Cooperation is done to provide information sharing, computational speedups, modularity and convenience.

Blocking

A process that is blocked is one that is waiting for some event, such as a resource becoming available or the completion of an I/O operation. In a multitasking computer system, individual tasks, or threads of execution, must share the resources of the system.

search time (rotational delay)

A rotational delay is the amount of time between information requests and how long it takes the hard drive to move to the sector where the requested data is located. In other words, it is a time measurement, in ms (milliseconds), of how long before a rotating drive can transfer data.

Access Control List (ACL)

A set of permissions that is attached to an object.

Safe State

A state is safe if the system can allocate all resources requested by all processes ( up to their stated maximums ) without entering a deadlock state. ... If a safe sequence does not exist, then the system is in an unsafe state, which MAY lead to deadlock.

Movable-head

A type of disk drive in which read/write heads are moved over the surface of the disk, toward and away from the center, so that they are correctly positioned to read or write the desired information.

Directed Graphs

A wait-for graph in computer science is a directed graph used for deadlock detection in operating systems and relational database systems.

Access Control Matrix

An internally maintained table specifying which portions of the system users are permitted to access and what actions they can perform.

Record Format

Any method of encoding audio and/or video signals on a storage medium.

Mutual Exclusion

At least one resource must be held in a non-shareable mode. Otherwise, the processes would not be prevented from using the resource when necessary.

In parallel computations, mutual exclusion is achieved automatically because each operation is handled in order, one at a time.

False

Levels in a file management system

File attributes File operations File access permission File systems

File names

Files should be stored in named folders with appropriate file names that will make it easy to find files.

Which of the following is the first step in reducing a directed graph to eliminate deadlock?

Find a process that is currently using a resource and not waiting for one.

P(s) test- wait

If the value of semaphore variable is not negative, decrement it by 1. If the semaphore variable is now negative, the process executing wait is blocked (i.e., added to the semaphore's queue) until the value is greater or equal to 1. Otherwise, the process continues execution, having used a unit of the resource.

SCAN

In this algorithm, the disk arm moves into a particular direction till the end, satisfying all the requests coming in its path,and then it turns backand moves in the reverse direction satisfying requests coming in its path.

Fill in the missing event that causes deadlock in a database. There are two processes (P1 and P2), each of which needs to update two records (R1 and R2) and the following sequence leads to a deadlock: P1 accesses R1 and locks it. P2 accesses R2 and locks it. ____ P2 requests R1, which is locked by P1.

P1 requests R2, which is locked by P2.

Physical File Organization

Physical files contain the actual data that is stored on the system, and a description of how data is to be presented to or received from a program. They contain only one record format, and one or more members. Records in database files can be externally or program-described.

variable-length records

Records whose length is not determined in advance. Each record is allocated the space that it needs to store the information it holds. See also the definition for "fixed-length record".

fixed-length records

Records whose size is determined in advance. All such records in a file have the same length. See also the definition for "variable-length records".

Resource Holding

Resources cannot be removed from the processes are used to completion or released voluntarily by the process holding it. The processes in the system form a circular list or chain where each process in the list is waiting for a resource held by the next process in the list.

Capability lists

Rows of the access matrix

Access methods

Sequential Access: records must be retrieved in order. Direct Access: records can be retrieved in any order.

SSTF

Shortest seek time first, is a form of SJF but may cause starvation of some requests.

seek time

The time it takes for a read/write head to move to a specific data track; one of the delays associated with reading or writing data on a computer disk drive.

When using the WAIT and SIGNAL operations, ____ sets the process's process control block to the blocked state and links it to the queue of processes waiting to enter this particular critical region.

WAIT

Volume configuration

With volume configuration, each volume in the system is given a name. The file manager writes this name and other descriptive information or the first sector of the outermost track of the disk pack.

Inter-record gap (IRG)

a break between data records on hard drive and magnetic tape to prevent data overwrites. Interrecord gaps are also used as a marker for the end of data.

Critical region

a code segment that accesses shared variables and has to be executed as an atomic action.

data file

a computer file which stores data to be used by a computer application or system, including input and output data. A data file usually does not contain instructions or code to be executed (that is, a computer program).

Extents

a contiguous area of storage reserved for a file in a file system, represented as a range of block numbers. A file can consist of zero or more extents; one file fragment requires one extent.

Sequential access media

a group of elements (such as data in a memory array or a disk file or on magnetic tape data storage) is accessed in a predetermined, ordered sequence. Sequential access is sometimes the only way of accessing the data, for example if it is on a tape.

Master/Slave

a model of communication where one device or process has unidirectional control over one or more other devices. In some systems a master is selected from a group of eligible devices, with the other devices acting in the role of slaves.

Seek Strategy

a predetermined policy used by the I/O device handler to optimize seek times

Recovery

a process of salvaging (retrieving) inaccessible, lost, corrupted, ... The most common data recovery scenario involves an operating system failure, malfunction of a storage device, logical failure of storage devices, ...

Mutex

a program object that is created so that multiple program thread can take turns sharing the same resource, such as access to a file.

No Preemption

a resource can be released only voluntarily by the process holding it.

Direct access storage devices (DASD)

a secondary storage device in which "each physical record has a discrete location and a unique address".

deadlock

a situation in which two computer programs sharing the same resource are effectively preventing each other from accessing the resource, resulting in both programs ceasing to function.

lock

a synchronization mechanism for enforcing limits on access to a resource in an environment where there are many threads of execution. A lock is designed to enforce a mutual exclusion concurrency control policy.

Contiguous Storage

a type of file storage in which all the information is stored in adjacent locations in a storage medium

Noncontiguous storage

a type of file storage in which the information is stored in nonadjacent locations in a storage medium

Loosely Coupled System

a type of multiprocessing where the individual processors are configured with their own memory and are capable of executing user and operating system instructions independent of each other. This type of architecture paves the way for parallel processing.

Semaphore

a variable or abstract data type used to control access to a common resource by multiple processes in a concurrent system such as a multitasking operating system. ... That system eventually became known as THE multiprogramming system.

Indexed sequential record organization

a way of organizing data in a direct access storage device. An index is created to show where the data records are stored. Any data record can be retrieved by consulting the index first.

Indexed Storage

allows direct record access, every file has own index block, supports sequential and direct access, does NOt necesarly improve storage space use.

Rotational ordering

an algorithm used to reorder record requests within tracks to optimize search time.

Test and Set

an instruction used to write 1 (set) to a memory location and return its old value as a single atomic (i.e., non-interruptible) operation.

first come first served (FCFS)

an operating system process scheduling algorithm and a network routing management mechanism that automatically executes queued requests and processes by the order of their arrival.

COEND

command used with COBEGIN to indicate to a multiprocessing compiler the end of a section where instructions can be processed concurrently

COBEGIN

command used with COEND to indicate to multiprocessing compiler the beginning of a section where instructions can be processed concurrently

Program file

contains instructions that allow the computer to perform various functions executed by the user.

A ____ of processing must be handled as a single unit.

critical region

lossless data compression

data compression technique where the number of bits needed to store or transmit information is reduced and the original data can be completely reconstructed

lossy data compression

data compression technique where the number of bits needed to store or transmit information is reduced, but the original data cannot be reconstructed

Field

data that has several parts, known as a record, can be divided into fields. Relational databases arrange data as sets of database records, also called rows. Each record consists of several fields; the fields of all records form the columns. These are placeholders for data that might change.

Prevention

deadlock prevention algorithms are used in concurrent programming when multiple processes must acquire more than one shared resource. ... A deadlock prevention algorithm organizes resource usage by each process to ensure that at least one process is always able to get all the resources it needs.

Circular Wait

each process must be waiting for a resource which is being held by another process, which in turn is waiting for the first process to release the resource.

In general, operating systems must either choose avoidance or recovery as a strategy for dealing with deadlocks.

false

Direct record organization

files stored in a direct access storage device and organized to give users the flexibility of accessing any record at random, regardless of its position in the file.

Unsafe State

if there is no allocation sequence that allows the processes to finish executing, then the system is in an unsafe state.

file descriptor

information kept in the directory to describe a file or file extent.

Optical Disc Storage

is more like a record -same sized sectors from center to disc CLV(constant linear velocity) -more data than magnetics

Most current operating systems support the implementation of threads, or ____, which have become part of numerous application packages.

lightweight processes

____ is necessary in any computer system because some resources such as memory, CPU, and dedicated devices must be exclusively allocated to one user at a time.

mutual exclusion

starvation

normally caused by deadlock in that it causes a process to freeze. ... A possible solution to starvation is to use a scheduling algorithm with priority queue that also uses the aging technique. Aging is a technique of gradually increasing the priority of processes that wait in the system for a long time.

Deadlock Detection

process of actually determining that a deadlock exists and identifying the processes and resources involved in the deadlock. The basic idea is to check allocation against resource availability for all possible allocation sequences to determine if the system is in deadlocked state a.

Failure to lock database records before updating them may result in a ____ between processes.

race

Multiprocessing

refers to the use of two or more central processing units (CPU) within a single computer system. These multiple CPUs are in a close communication sharing the computer bus, memory and other peripheral devices. These systems are referred as tightly coupled systems.

Process synchronization

sharing system resources by processes in a such a way that, Concurrent access to shared data is handled thereby minimizing the chance of inconsistent data. Maintaining data consistency demands mechanisms to ensure synchronized execution of cooperating processes.

Subdirectories

smaller groupings of files within a directory

A problem with test-and-set is that when many processes are waiting to enter a critical region, ____ can occur because the processes gain access in an arbitrary fashion.

starvation

The ____ multiprocessing configuration is the most difficult to implement because the processes must be well synchronized to avoid races and deadlocks.

symmetric

Current byte address (CBA)

the address of the last byte read. It is used by the File Manager to access records in secondary storage and must be updated every time a record is accessed.

access time

the amount of time it takes the processor to read data, instructions, and information from memory