CH 10 OPERATING SYSTEMS
Single Contiguous Memory Management
-A logical address is simply an integer value relative to the starting point of the program -A physical address is a logical address added to the starting location of the program in main memory
Operating System
-Manages computer resources, such as memory and input/output devices -Provides an interface through which a human can interact with the computer -Allows an application program to interact with these other system resources
Resource Management
-Multiprogramming -Memory Management -Process -Process Management -CPU Scheduling
Process Management- Context Swtich
-Register values for the currently running process are stored into its PCB -Its PCB is moved to the list of the state into which it goes -Register values of the new process moving into the running state are loaded into the CPU -This exchange of register information is called a context switch
Memory Management
-Track where and how a program resides in memory -Convert logical addresses into actual addresses(physical)
Process Control Block (PCB)
A data structure used by the OS to manage information about a process, including: -Current value of the program counter -Values of all CPU registers for the process -Base and bound register values (or page tables) -Accounting information
Page
A fixed-size portion of a process that is stored into a memory frame (page and frame are same size)
Frame
A fixed-size portion of main memory that holds a process page
Process
A program in execution
PMM Base Register
A register that holds the beginning address of the current partition (the one that is running)
PMM Bounds Register
A register that holds the length of the current partition
Device Driver
A small program that "knows" the way a particular device expects to receive and deliver information
Real-Time System
A system in which response time is crucial given the nature of the application
Timesharing System
A system that allows multiple users to interact with a computer at the same time
Paged Memory Technique
A technique in which processes are divided into fixed-size pages and stored in memory frames when loaded
Physical Address
Actual address in main memory
Page Number
Address divided by the page size
First fit
Allocate program to the first partition big enough to hold it
Worst fit
Allocate program to the largest partition big enough to hold it
Best fit
Allocated program to the smallest partition big enough to hold it
Demand Paging
An extension of paged memory management in which pages are brought into memory on demand
"sharing nicely"
An operating system manages resources, and these resources are often shared in one way or another among programs that want to use them
CPU Scheduling-
Determining which process in memory is executed by the CPU at any given point
Partition Memory Management
Divided into partitions: -Fixed partitions Main memory is divided into a fixed number of partitions into which programs can be loaded -Dynamic partitions Partitions are created as needed to fit the programs waiting to be loaded
Round Robin
Each process runs for a specified time slice and moves from the running state to the ready state to await its next turn if not finished
CPU Scheduling Algorithms
First come first served Shortest job next Round Robin
Partition Selection Algorithms
First-fit Best-fit Worst-fit
Thrashing
Inefficient processing caused by constant page swaps
Paged Memory Management
Paged Memory Technique Frame Page Demand Paging Page Swap Virtual Memory Thrashing
Shortest Job Next
Process with shortest estimated running time in the ready state is moved into the running state first
First-Come, First-Served
Processes are moved to the CPU in the order in which they arrive in the running state
Logical Address
Reference to a stored value relative to the program making the reference
System Software
Software that manages a computer system at a fundamental level
Application Software
Software written to address specific needs—to solve problems in the real world
Software Categories
Systems Software and Applications Software
Page Swap
The act of bringing in a page from secondary memory, which often causes another page to be written back to secondary memory
Process Managament
The act of carefully tracking the progress of a process and all of its intermediate states
CPU Scheduling
The act of determining which process in the ready state should be moved to the running state -Many processes may be in the ready state -Only one process can be in the running state, making progress at any one time
Process Management
The act of managing the use of the CPU by individual processes
Turnaround Time
The amount of time between when a process arrives in the ready state the first time and when it exits the running state for the last time
Round Robin- Time Slice (Quantum)
The amount of time each process receives before being preempted and returned to the ready state to allow another process its turn
Nonpreemptive Scheduling
The currently executing process gives up the CPU voluntarily
Batch Processing
The first operating system was a human operator, who organized various jobs from multiple users into batches of jobs that needed the same resources.
Virtual Machine
The illusion created by a time-sharing system that each user has his/her own machine
Virtual Memory
The illusion that there are no restrictions on the size of a program because an entire process doesn't have to be in memory at the same time
Preemptive Scheduling
The operating system decides to favor another process, preempting the currently executing process
Memory Management
The process of keeping track of what programs are in memory and where in memory they reside
Offset
The remainder of the address divided by the page size
Multiprogramming
The technique of keeping multiple programs that compete for access to the CPU in main memory at the same time so that they can execute
Response Time
The time delay between receiving a stimulus and producing a response
Timesharing
Timesharing system and Virtual Machine
Single Contigous MM
has only the OS and one other program in memory at one time
Partition Memory Management
has the OS and any number of other programs in memory at one time
