Operating Systems Concepts Chapters 1-4

Another set of OS functions exists for ensuring the efficient operation of the system itself via resource sharing

Resource Allocation, Accounting, Protection, and Security

A modern general-purpose computer system consists of what?

one or more CPUs and a number of device controllers connected through a common bus that provides access to shared memory

User goals

operating system should be convenient to use, easy to learn, reliable, safe, and fast

System goals

operating system should be easy to design, implement, and maintain, as well as flexible, reliable, error-free, and efficient

The parent process may wait for termination of a child process by using the ______ system call.

wait()

When does a program become a process?

when an executable file is loaded into memory

Direct Memory Access (DMA)

After setting up buffers, pointers, and counters for the I/O device, the device controller transfers an entire block of data directly to or from its own buffer storage to memory, with no intervention by the CPU. Only one interrupt is generated per block, to tell the device driver that the operation has completed, rather than the one interrupt per byte generated for low-speed devices. While the device controller is performing these operations, the CPU is available to accomplish other work.

I/O-bound process

spends more time doing I/O than computations, many short CPU bursts

Process

A program in execution

What is an Operating System?

A program that acts as an intermediary between a user of a computer and the computer hardware

Shared memory

A region of memory that is shared by cooperating processes is established. Processes can then exchange information by reading and writing to data to the shared region.

Timesharing

CPU switches jobs so frequently that users can interact with each job while it is running, creating interactive computing

fault tolerant Systems

Can suffer a failure of any single component and still continue operation

When a process creates a new process, there are also two address-space possibilities for the new process:

Child duplicate of parent; Child has a new program loaded into it

Reasons a parent might end a child process:

Child has exceeded allocated resources; Task assigned to child is no longer required; The parent is exiting and the operating systems does not allow a child to continue if its parent terminates

Two ways for users to interface with the operating system:

Command-line interface, or command, Graphical user interface (GUI)

Message passing

Communication takes place by means of messages exchanged between the cooperating processes

Interrupt Vector

Contains the addresses of all the interrupt service routines

An operating system is a control program

Controls execution of programs to prevent errors and improper use of computer

Asymmetric Multiprocessing

Each processor is assigned a specific task. A boss processor controls the system; the other processors either look to the boss for instruction or have predefined tasks.

Symmetric Multiprocessing (SMP)

Each processor performs all tasks within the operating system. Processors are peers.

Benefits of Microkernel System Structure

Easier to extend a microkernel, Easier to port the operating system to new architectures, More reliable (less code is running in kernel mode), More secure

Operating system goals:

Execute user programs and make solving user problems easier, Make the computer system convenient to use, Use the computer hardware in an efficient manner

System Program Categories

File management, Status information, File modification, Programming language support, Program loading and execution, Communications, Background services

Multiprocessors systems (parallel systems, multicore systems)

Have two or more processors in close communication, sharing the computer bus and sometimes the clock, memory and peripheral devices

Resource Utilization

How various hardware and software resources are shared

Cascading Termination

If a process terminates, then all its children must also be terminated

Where is a new process put initially?

In the ready queue

Advantages of multiprocessor systems

Increased throughput (more processors = more work done in less time), Economy of scale (cost less than multiple single-processor systems, because they share peripherals mass storage, and power supplies), Increased reliability (failure of one processor will not halt the system, only slow it down)

Multiprogramming

Increases CPU utilization by organizing jobs (code and data) so that the CPU always has one to execute

Caching

Information in use copied from slower to faster storage temporarily

Reasons for cooperating processes:

Information sharing, Computation speedup, Modularity, Convenience

Bootstrap program

Initializes all aspects of the system, loads OS kernel and starts execution.

Running Process

Instructions are being executed

Clustered Systems

Like multiprocessor systems, but are composed of two or more systems joined together

Privileged instructions

Machine instructions that may cause harm and can only be executed in kernel mode

An operating system is a resource allocator

Manages all resources and decides between conflicting requests for fair and efficient resource use

What is the difference between policy and mechanism?

Mechanisms determine how to do something, policies decide what will be done

Microkernel System Structure

Moves as much from the kernel into user space

The differences between multiprocessor system and clustered system

Multiprocessor systems are closely coupled- multiple processors share the same memory. Clustered systems are loosely coupled- the multiple clusters each have their own memory but share the same storage

Process states

New, Running, Waiting, Ready, Terminated

Asymmetric Clustering

One machine is hot-standby mode while the other is running the applications. The hot-standby host machine does nothing but monitor the active server. If that server fails, the hot-standby host becomes the active server.

When a process creates a new process, two possibilities for execution exist

Parent and children execute concurrently; Parent waits until children terminate

Three resource sharing options for parent and children processes

Parent and children share all resources; Children share subset of parent's resources; Parent and child share no resources

Process Termination

Process executes last statement and then asks the operating system to delete it using the exit() system call.

The process control block contains many pieces of information associated with a specific process:

Process state, program counter, CPU registers, CPU-scheduling information, Accounting information, I/O status information

System Calls

Provide an interface to the services made available by an operating system

Where is the bootstrap program stored?

ROM or EEPROM

System-call Interface

Serves as the link to system calls made available by the operating system

Device Queues

Set of processes waiting for an I/O device. Each device has its own device queue

Two models of interprocess communication

Shared memory; message passing

Various ways to structure and operating system

Simple structure (MS-DOS), More complex (UNIX), Layered (an abstraction), Microkernel (Mach)

Application programming interface (API)

Specifies a set of functions that are available to an application programmer, including the parameter that are passed to each function and the return values the programmer can expect

Memory Controller

Synchronizes access to the memory to ensure orderly access to shared memory

Stack

Temporary data

What is included in a process?

Text section, Current activity, Stack, Data section, Heap

Graceful Degradation

The ability to continue providing service proportional to the level of surviving hardware

Two approaches to implementing a command interpreter

The command interpreter itself contains the code to execute the command or it implements most commands through system programs (The command interpreter does not understand the command in any way; it merely uses the command to identify a file to be loaded into memory and executed)

I/O operation

The device driver loads the appropriate registers within the device controller. The device controller, in turn, examines the contents of these registers to determine what action to take (such as "read a character from the keyboard "). The controller starts the transfer of data from the device to its local buffer. Once the transfer of data is complete, the device controller informs the device driver via an interrupt that it has finished its operation. The device driver then returns control to the operating system, possibly returning the data or a pointer to the data if the operation was a read.

Loadable Kernel Modules

The kernel has a set of core components and links in additional services via modules, either at boot time or during run time

Kernel

The one program running at all times on the computer

Layered Approach

The operating system is divided into a number of layers (levels), each built on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface.

Once a process is allocated the CPU and is executing, one of several events could occur:

The process could issue an I/O request and then be placed in an I/O queue. The process could create a new child process and wait for the child's termination. The process could be removed forcibly from the CPU, as a result of an interrupt, and be put back in the ready queue.

Waiting process

The process is waiting for some event to occur

Ready Process

The process is waiting to be assigned to a processor

Text Section

The program code

Current activity

The value of the program counter and the contents of the processor registers

Symmetric Clustering

Two or more hosts are running applications and monitoring each other

Device Driver

Understands the device controller and provides the rest of the operating system with a uniform interface to the device

One set of operating-system services provides functions that are helpful to the user:

User Interface, Program Execution, I/O Operations, File-System Manipulation, Communications, Error Detection

What are the two separate modes of operation?

User mode (1) and kernel mode (0)

Context Switch

a state save of the current state of the CPU, be it in kernel or user mode, and then a state restore to resume operations

Parent may terminate the execution of children processes using the _______ system call

abort()

Dual-mode operation

allows OS to protect itself and other system components

Cooperating process

can affect or be affected by the execution of another process

Independent process

cannot affect or be affected by the execution of another process

Heap

contains memory dynamically allocated during run-time

fork() system call

creates new process

Application Programs

define the ways in which the system resources are used to solve the computing problems of the users (Word processors, compilers, web browsers, database systems, video games)

parallelization

divides a program into separate components that run in parallel on individual computers in the cluster

What do users want from an operating system?

ease of use, and performance

Interrupt Service Routine

examines the interrupt and determines how to handle it

Data section

global variables

Three general methods used to pass parameters to the OS

pass the parameters in registers, Parameters stored in a block, or table in memory, and address of block passed as a parameter in a register, Parameters placed, or pushed, onto the stack by the program and popped off the stack by the operating system

Types of System Calls

process control, file management, device management, information maintenance, communications, protection

System programs

provide a convenient environment for program development and execution

Hardware

provides basic computing resources (CPU, memory, I/O devices)

Device controller

responsible for moving the data between the peripheral devices that it controls and its local buffer storage

Process scheduler

selects among available processes for next execution on CPU

Job Queue

set of all processes in the system

Ready Queue

set of all processes residing in main memory, ready and waiting to execute

On systems with multiple command interpreters to choose from, the interpreters are known as __________.

shells

Interrupt

signals the occurrence of an event from either hardware or sofware

Trap or Exception

software-generated interrupt caused either by an error or a user request

CPU-bound process

spends more time doing computations; few very long CPU bursts

When an interrupt occurs, the system needs to save...

the current context of the process running on the CPU so that it can restore that context when its processing is done

An interrupt transfer control to ___________________.

the interrupt service routine

What is the main function of the command interpreter

to get and execute the next user-specified command

What does the Operating System control and coordinate?

use of hardware among various applications and users

exec() system call

used after a fork() to replace the process' memory space with a new program