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Section 1

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Alternative I/O Structures

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Mar 14, 2020

Cards (49)

Section 1

(49 cards)

Alternative I/O Structures

Front

After I/O starts, control returns to user program only upon I/O completion (Synchronous). After I/O starts, control returns to user program without waiting for I/O completion (Asynchronous).

Back

Advantages of parallelsystem

Front

Increased throughput - Economical - Increased reliability graceful degradation fail-soft systems

Back

Parallel Systems

Front

Multiprocessor systems with more than one CPU in close communication Tightly coupled System Loosely coupled system

Back

Diffrent views of what an OS is

Front

1. Resource allocator 2.Control program

Back

Common Functions of Interrupts

Front

• Provides hardware supported asynchronous communication between computer components • Interrupts transfers instruction execution to the interrupt service routine, generally through the interrupt vector, which contains the addresses of all the service routines. • Interrupt hardware architecture must save the address of the interrupted instruction. • Incoming interrupts are disabled or queued while another interrupt is being processed to prevent a lost interrupt. • A trap or an exception is a software-generated interrupt caused either by an error or a user request. • An operating system is interrupt driven.

Back

Dual-Mode

Front

Sharing system resources requires operating system to ensure that an incorrect program cannot cause other programs to execute incorrectly. Must ensure that a user program could never gain control of the computer in kernel mode two modes: 1.user mode 2.Kernel mode

Back

Direct Memory Acess

Front

• Used for high-speed I/O devices able to transmit information at close to memory speeds. • Device controller transfers blocks of data from buffer storage directly to main memory without CPU intervention. • Only one interrupt is generated per block of data transferred, rather than one interrupt per byte delivered to CPU.

Back

Main memory

Front

only large storage media that the CPU can access directly - usually volatile.

Back

Secondary storage

Front

extension of main memory that provides large nonvolatile storage capacity

Back

Storage Hierarchy

Front

- Speed - cost - volatility

Back

Protection Hardware

Front

• When executing in monitor mode, the operating system has unrestricted access to both monitor and user's memory. • The load instructions for the base and limit registers are privileged instructions.

Back

Resource allocator

Front

manages and allocates resources

Back

Spooling

Front

- Reads next job from card reader into a storage area on the disk (job queue). - Outputs printout of previous jobs from disk to one or more printers. - SPOOL == simultaneous peripheral operations on-line

Back

O/S Kernel

Front

the one program running at all times (all else being application programs and system utility programs)

Back

User mode

Front

execution done on behalf of a user

Back

Asymmetric Multiprocessing

Front

- "Slave" processors assigned a specific task by a "master" processor that schedules and allocates work - More common in extremely large systems

Back

Mode bit

Front

added to computer hardware to indicate the current mode: kernel (0) or user (1).

Back

I/O Protection

Front

Operating system must manage resources accessed through I/O that are not usually sharable and usually need to be dedicated to a process for a defined period of time. • All I/O instructions are privileged instructions to force user programs to send requests the operating system to perform any I/O operation. • Forces all user programs to "play by the rules" with respect to non-sharable, dedicated resources.

Back

System Call

Front

the method used by a process to request action by the operating system.

Back

Operating System goals

Front

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

Back

Job pool

Front

data structure that allows the OS to select which job to run next in order to increase CPU utilization

Back

Cache memory

Front

modest amount of fast access storage that hardware uses to make main memory access more efficient

Back

System and application programs

Front

define the ways in which the system resources are used to solve the computing problems of the users (compilers, database systems, video games, business programs)

Back

I/O devices

Front

keyboards, mice, display screens, small printers.

Back

Kernel Mode

Front

execution done on behalf of operating system.

Back

Hardware

Front

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

Back

Hardware Supported Memory Protection

Front

Must provide memory protection at least for the interrupt vector and the interrupt service routines. • Normally want to provide memory protection for all users • Memory outside the defined range is protected. • In order to have memory protection, add two hardware registers that determine the range of legal addresses a program may access: 1.base register 2.Limit register

Back

limit register

Front

contains the size of the range

Back

Operating System

Front

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

Back

CPU Protection

Front

Timer - interrupts computer after specified period to ensure operating system maintains control. - Timer is implemented in hardware logic - Timer is decremented every clock tick. - When timer reaches the value 0, an interrupt occurs. • Timer commonly used to implement time sharing. • Timer can also used to compute the current time. • Load-timer is a privileged instruction.

Back

Control Cards

Front

Special cards that tell the resident monitor which programs to run Special characters distinguish control cards from data or program cards First us of OS commands

Back

Computer System Componets

Front

1.Hardware 2.Operating System 3. System and application programs 4.Users

Back

Symmetric Multiprocessing

Front

- Each processor independently executes a task and uses the same operating system. - Many processes can run at once without performance deterioration. - Most modern operating systems support SMP

Back

Simple Batch Systems

Front

Employed a computer operator • User ≠ operator • Add a card reader for "high speed" input • Reduce setup time by batching similar jobs • Automatic job sequencing - automatically transfers control from one job to another. First rudimentary operating system. • Resident "monitor"

Back

Operating system

Front

controls and coordinates the use of the hardware among the various application programs for the various users.

Back

Off-Line I/O Operations

Front

Attempt to attain higher efficiency Moves data on cards or paper tape to magnetic tape using a machine programmed only for that purpose Move data on magnetic tape to cards, paper tape or printed pages using a machine programmed only for that purpose

Back

OS features needed for Multiprogramming

Front

1.I/O routine supplied by the system 2.Memory management 3.CPU scheduling Allocation of devices to jobs

Back

Caching

Front

copying information into faster storage system; main memory can be viewed as a cache for secondary storage. Requires a cache management policy. This requires data that is simultaneously stored in more than one level to be consistent. • Term also for use of high-speed memory to hold recentlyaccessed data. • High-speed memory caching introduces another level in storage hierarchy

Back

register

Front

small, but fast access areas of storage, that a CPU can access directly

Back

Interrupt Handling

Front

• The operating system preserves the state of the CPU by storing registers and the program counter. • Determines which type of interrupt has occurred: - polling - vectored interrupt system • Separate segments of code determine what action should be taken for each type of interrupt

Back

Storage Structure

Front

1.Main memory 2.Registers 3.Cache memory 4.Seconfary storage

Back

Loosely coupled system

Front

independent computers share work through message passing

Back

Tightly coupled system

Front

processors share memory and a clock; communication usually takes place through the shared memory

Back

Base Register

Front

holds the smallest legal physical memory address

Back

Control program

Front

controls the execution of user programs and operations of I/O devices.

Back

Hardware-based Protection

Front

Computer system hardware can be designed to support the protection capabilities required by the operating system. • In fact, protection could not be implemented adequately in O/S software alone - but must have hardware support.

Back

Personal computers

Front

Computer system dedicated to a single user User convenience and responsiveness Could adopt technology developed for larger operating systems

Back

Computer-System Operation-I/O

Front

• I/O devices and the CPU can execute concurrently. • Each device controller is in charge of a particular device type. • Each device controller has a local buffer. • CPU moves data from/to main memory to/from controller buffers • I/O is from the device to local buffer of controller. • Device controller informs CPU that it has finished its operation by causing an hardware interrupt.

Back

How Does O/S Maintain I/O Control?

Front

System Call

Back