ITEC 274 Midterm

ASCII

(American Standard Code for Information Interchange) is a code for representing 128 English characters as numbers, with each letter assigned a number 0 to 127

File

- a collection of data or information stored in a computer must be in a file. There are many different types of files store different types of information.

Virtual memory

A system with ____ divides programs into parts and keep them in secondary storage, bringing each part into memory only as it is needed.

overhead

By compacting and relocating, the operating system optimizes the use of memory and thus improves throughput. However, it also requires more ____ than the other memory allocation schemes.

Binary

Computers are based on ____, wis comprised of 0 and 1, which explains common numbers like 2, 4, 8, 16, 32, 64, 128, 256, etc.

Swapped

In demand paging, pages are ____ between main memory and secondary storage.

working set

In demand paging, the collection of pages residing in memory that can be accessed directly without incurring a page fault is called the

thrashing

In demand paging, when an excessive number of pages are moved back and forth between main memory and secondary storage, it is called

random access memory

Main memory is also known as

User Interface

The ____ determines how one interacts with a computer sysytem and is often very different from one operating system to the next, sometimes even between different versions of the same operating system.

interrupt

The most common mechanism for implementing multiprogramming was the introduction of the ____ concept, whereby the CPU was notified of events needing operating systems services.

internal fragmentation

The phenomenon of less-than-complete use of memory space in a fixed partition is called ____.

Memory compaction

The process of collecting fragments of available memory space into contiguous blocks by relocating programs and data in a computer's memory.

deallocation

The release of memory space by the operating system.

Software

a collection of programs used to perform certain tasks. They fall into three main categories: operating system programs, compilers and assemblers, and application programs

Server

a node that provides to client's various network services such as file retrieval, printing, or database access services.

Network

a system of interconnected computer systems and peripheral devices that exchange information with one another

Client

a user node that requests and makes use of various network services. A workstation requesting the contents of a file from a file server is a client of the file server.

Virtualization

allows separate partitions of a single server to support different operating systems.

Demand paging and thrashing

an excessive number of pages are moved back and forth between main memory and secondary storage.

External Fragmentation

consists of fragments of free memory between blocks of allocated memory.

Two main categories of files on a computer

data file that is stored, and program that is executable

Virtual memory

divides programs into parts and keeps them in secondary storage, bringing each part into memory only as it is needed. It effectively removes restrictions on maximum program size.

Circular wait

each process is waiting for another to voluntarily release so at least one can continue (each person involved in the impasse is waiting for another to voluntarily release the step so at lease one can continue and get to their destination)

Virtual Memory

effectively removes restrictions on maximum program size.

Unicode

is a 16 bit coding scheme that is capable of representing more than 65,000 characters / symbols.

Disk drive

is a device which allows a computer to read from and write on to computer disks

Folder

is an icon on a computer screen that can be used to access a directory containing related files or documents.

Main memory

is where the data and instructions of a computer must reside to be processed.

No preemption

lack of temporary reallocation of resources (each step is dedicated to the climber; it is allocated to the holder for as long as needed)

The primary advantage of storing programs in noncontiguous locations is that

main memory is used more efficiently

Resource holding

not releasing the resource; waiting for other job to retreat

Compaction

of memory is performed by the operating system to reclaim fragmented sections of the memory space.

deadlock

refers to a specific condition/problem in multiprocessing enviroment when two or more processes are each waiting for another to release a resource, or more than two processes are waiting for resources in a circular chain.

Demand paging and working set

the collection of pages residing in the memory that can be accessed directly without incurring a page fault.

Hardware

the physical machine and its components, including main memory, I/O devices, I/O channels, direct access storage devices, and the central processing unit.

Information technology

the study or use of systems for storing, retrieving, and sending information. Information systems is formal, sociotechnical, organizational systems designed to collect, process, store, and distribute information.

Understanding of Deadlock, Livelock, Starvation

• A problem occurring when the resources needed by some jobs to finish execution are being held by other jobs, which in turn, are waiting for other resources to become available. Deadlock neither process is blocked or waiting; they are both in a continuous state of change. • A locked system whereby two or more processes continually block the forward progress of the others without making any forward progress itself. • The result of a conservative allocation of resources in which a single job is prevented from execution because it's kept waiting for resources that never become available.

Concurrent Programming

• A programming technique that allows a single processor to simultaneously execute multiple sets of instructions. (Multitasking)

Multiprogramming

• A single processor can run several programs found in the main memory, that all share the same CPU. • The Processor is allocated to each job or each process for a time period and then Deallocated at the appropriate moment, which is a delicate task.

Spooling

• A technique developed to speed I/O by collecting in a disk file either input received from slow input devices or output going to slow output devices such as printers. • Spooling minimizes the waiting done by the processes performing the I/O.

Understanding of core portion of an operating system or kernel

• CPU, RAM, I/O device • Kernal: The name for the core portion of an operating system • Needs CORRECTION

Real-time system

• Computing systems used in time-critical environments that require guaranteed response times, such as in navigation, rapid transit, and industrial control systems.

Scheduling Algorithms

• First-come, first-served (FCFS): Nonpreemptive, The job is handled based on it's arrival time. The earlier it arrives, the earlier it is served. Uses FIFO queue. Good for batch systems, but unacceptable in interactive systems because of unpredictable turnaround time • Shortest job next (SJN): Nonpreemptive, the Job is handled based on the length of the CPU cycle time. Good for batch systems, but not good in interactive systems. • Priority scheduling: Nonpreemptive: preferential treatment for important jobs, the highest priority programs processed first. No interrupts until CPU cycles are completed or natural wait occurs. Processor Scheduler manages multiple READY queues. • The shortest remaining time (SRT): Preemptive version of SJN, The Processor is allocated to the job closest to completion, it's Preemptive if the newer job has a shorter completion time.

Starvation avoidance strategies

• Implement algorithm tracking to see how long each job has been waiting for resources, and once starvation is detected block new jobs until starving jobs are satisfied.

Cache memory

• Intermediary between main memory and the special purpose registers, which are the domain of the CPU.

User Interface

• It is a portion of the operating system that users interact with directly

Definition of firmware

• It is used to indicate a program that is permanently held in ROM, as opposed to being held in secondary storage.

Operating System & main fucntions

• It's the chief software component of a computer system, responsible for managing memory, processor(s), devices, files. and providing a user interface. The operating system consists of four subsystems: process management, memory management, input/output management, and file management.

Concepts of three tables for tracking pages: Job Table (JT), Page Map Table (PMT), and Memory Map Table (MMT)

• Job Table (JT): information for each active job such as job size, and memory location (jobs PMT) • Page Map Table (PMT): Information for each table such as Page number (beginning with page 0), and memory address. • Memory Map Table (MMT): Entry for each page such as location, and free/busy status.

Job and Process States, HOLD, READY, WAITING, RUNNING, FINISHED

• Job accepted -Put on HOLD and placed in queue • Job state changes from HOLD to READY -Indicates job waiting for CPU • Job state changes from READY to RUNNING -When selected for CPU and processing • Job state changes from RUNNING to WAITING -Requires unavailable resources: moves back to READY status • Job state changes to FINISHED -Job completed (successfully or unsuccessfully)

Levels of Multiprocessing. Multiprocessing occurs at three levels (Job level, Process level, Thread level)

• Job level: Each job has its own processor, and all processes and threads are run by that same processor. • Process Level: Unrelated processes, regardless of job, can be aligned to available processors. • Thread level: Threads, regardless of job and process, can be assigned to available processors.

Single-user system and job are processing

• Jobs are processed sequentially. Interrupt and reason for it • It was used to implement multiprogramming. When an interrupt occurs the CPU is notified of events needing the operating systems services. • Calls for help, activates higher priority program.

Definition of Main memory

• Main memory refers to physical memory that is internal to the computer. The word main is used to distinguish it from external mass storage devices such as disk drives. Other terms used to mean main memory include RAM and primary storage. The computer can manipulate only data that is in the main memory. The memory unit that works directly with the CPU, and in which the data and instructions must reside in order to be processed. Also known as Random Access Memory.

Understanding of the five subsystem managers

• Memory manager, Processor Manager, Device Manager, File Manager, User interface, Network Manager

Multiprogramming environment

• Multiple processes competing to be run by a single CPU. It requires a fair and efficient CPU allocation for each job.

Few Examples of Deadlock

• Nonsharable/non-preemptable resources that are allocated to jobs requiring same type of resources, and Resource types that are locked by competing jobs.

Mutual exclusion

• One of the four conditions that result in a deadlock in which only one process is allowed to have access to a resource. ONE to ONE

Page Replacement Policies and Concepts (FIFO) policy and (LRU) policy

• Page Replacement Policies and Concepts: An algorithm used by virtual memory systems to decide which page or segment to remove from main memory when a page frame is needed and memory is full. • (FIFO) First-In-First-Out policy: The Best page to remove is the page that's been in memory longest. • (LRU) Least-Recently-Used policy: The Best page to remove is the page that was least recently accessed.

General understanding of the Evolution of virtual memory (Paged, demand paging, segmented, segmented/demand paging)

• Paging is a memory management scheme that eliminates the need for contiguous allocation of physical memory. • In Segmented Paging, the main memory is divided into variable size segments which are further divided into fixed-size pages. • Demand paging is a type of swapping in which pages of data are not copied from disk to RAM until they are needed. Pages are swapped between main directory and secondary storage.

Compaction of memory

• Performed by the operating system to reclaim fragmented sections of the memory space. • Optimizes memory use and improves throughout, but it requires more overhead • Timing: When a certain memory percentage is busy, when there are waiting for jobs, and after a prescribed time period has elapsed

Definitions of Processor (CPU), Program (job), Process (task), and Thread

• Performs calculations and executes programs. It makes a job active. • Inactive unit, a file stored on a disk, or a Unit of work submitted by the user. • An Active entity that requires resources (processor, special registers, etc.) to perform a function. Executable program single instance. A job that has been divided into multiple processes. • A Portion of a process that runs independently. You can only address one at a time.

Definition of Multiprogramming and requirements

• Processor allocated to each job or each process for a time period • Deallocated at appropriate moment: delicate task

Fixed partitions

• Requires contiguous loading of the entire program • Multiprogramming • Main memory is partitioned • Each partition has one job • Partitions were static: reconfiguration requires system shut down • Protecting each job's memory size • Matching job size with partition size

Multicore technology

• Several processors placed on a single chip.

Understanding of the four types of memory allocation schemes

• Single-user systems: You can only load one thing at a time even if you have extra RAM. If your file is much larger than your RAM, then it will not allow you to load it. • Fixed Partitions: Main memory is divided into partitions with one partition = one job. Allows multiprogramming. • Dynamic Partitions: Partition sizes are determined by the first jobs loaded in. If you want to change them you need to reset your computer. • Relocatable Dynamic Partitions: The memory manager relocates programs, all of the fragmented blocks are compacted to create one memory block large enough to accommodate some or all waiting jobs.

Device driver

• Software that contains the detailed instructions required to start the device, allocate it to a job, use the device driver correctly, and deallocate it when appropriate.

Understanding of Processor Manager and its two submanagers (Job Scheduler and Process Scheduler)

• The Processor Manager is a compose of at least 2 submanagers (JS and PS) • Job Scheduler: Higher-level scheduler. Each job passes through a hierarchy of managers, the first one it encounters is the Job scheduler. It selects a job from the queue, places it in the process queue, and decides on the job initiation criteria. JH • Process Scheduler: Lower-level scheduler. It's in charge of Process scheduling responsibilities, process scheduling is based on certain criteria, and determines execution steps. PL

Cloud computing

• The practice of using Internet-connected resources to perform processing, storage, or other operations. It is important because it allows operating systems to accommodate remote access to system resources and provides increased security for these transactions.

Page Swapping process

• The process of moving a page out of main memory and into secondary storage so that another page can be moved into memory in its place.

What Is Parallel Processing? What Are the Benefits of Parallel Processing?

• The process of operating two or more CPUs executing instructions simultaneously. • Increased reliability • More than one CPU, If one processor fails, others take over: must be designed into the system • Faster processing and Instructions processed in parallel can process two or more at a time.

Threads and Concurrent Programming

• Threads are a smaller unit within a process. • It Minimizes overhead • Overhead is the swapping process between main memory and secondary storage. • Each active process thread shares data area and resources allocated to its process.

Understanding of the three dynamic partition system cases in Deallocation

• Three dynamic partition system cases in Deallocation; Case 1: adjacent to another free block, Case 2: between two free blocks, and Case 3: isolated from other free blocks.

First-fit memory allocation and Best-fit memory allocation

• the very first space found that is large enough and available, is the space the computer is going to fit the incoming job into. (1st found) • looks at the size of the incoming job, then it is going to look at each partition to see if it has enough capacity and if it's available, then it will look at the possible wasted space that would be created by placing that job in that partition. It will then place the incoming job into the partition that will create the least amount of wasted space. (Intelligence 1st found)

Internal fragmentation and external fragmentation

•A situation in which a fixed partition is only partially used by the program. The remaining space within the partition is unavailable to any other job and is therefore wasted. • A situation in which the allocation of memory creates unusable fragments of free memory between blocks of busy, or allocated, memory.

Memory Overhead & Manager

•Any combination of excess or indirect computation time, memory, bandwidth, or other resources that are required to perform a specific task. •The section of the operating system responsible for controlling the use of memory. It checks the validity of each request for memory space and, if it is a legal request it allocates the amount of memory needed to execute the job.