Understand I/O in Computer System - Coggle Diagram
Understand I/O in Computer System
Every transfer is an output from one device and an input into another.
Devices such as keyboards and mouses are input-only devices while devices such as printers are output-only.A writable CD-ROM is both an input and an output device.
The term I/O is used to describe any program,operation or device that transfers data to or from a computer and to or from a peripheral device.
I/O MODULE FUNCTION
Acts as an interface with the CPU and memory via the system bus or central switch.
Acts as an interface with one or more peripheral devices by tailored data links.
INPUT/OUTPUT DATA TRANSFER
Asynchronous Serial Transfer
Each character transmitter consists of start bit,character bits,and stop bits.
The first bit is called the star bit.It is always a 0 and isused to indicate the beginning of a character.
Asynchronous serial Transmission is character oriented.
The last bit called the stop bitis always a 1.In asynchronous transmission,binary information is sentonly when it is available and the line remain sidle when there is no information to be transmitted.
Asynchronous Communication Interface
The most significant aspect of a synchronous communications is variable bit rate,or that the transmitter and receiver clock generators do not have to be exactly synchronized.
Is the transmission of data without the use of an external clock signal,where data can be transmitted continuously rather than in a steady stream.
CHARACTERISTIC OF ISOLATED AND MEMORY MAPPED I/O
The processor and the I/O device have different memory located to each other.
Memory mapped I/O is one where the processor and the I/O device share the same memory location(memory).
Isolated I/O uses a special class of CPU instructions specifically for performing I/O.This is generally found on i intel microprocessors,specifically the IN and OUT instructions which can read and write one to four bytes(outb,outw,outl)to an I/O device.
Is the method of transferring data between theCPU and a peripheral such as a network adapter or an ATA storage device.
In general,programmed I/O happens when software running ontheR CPU uses instructions that access I/O address space to perform data transfers to or from an I/O device.
Programmed I/O refers to using input and output instructions to transfer data between memory and the registers on a peripheral interface
The best known example of a PC device that uses programmed I/O is the ATA interface.
Data are exchanged between the CPU and the I/O module.
When CPU issues a command to I/O module,it must wait until I/O operation is complete.
If the CPU is faster than I/O module,there is wastage of CPUtime.
Simple to implement
CPU is tied up for the duration of the transfer while doing are latively simple task
he process or does not have to repeatedly check the I/O module status.
No repeated CPU checking of device
I/O module interrupts when ready
Over comes CPU waiting
Over comes the process or having to wait long periods of time for I/O modules.
DIRECT MEMORY ACCES
Sometimes,CPU may not be fast enough to keep up with the peripheral.
In this casea special-purpose processor called a DMA controller(DMAC)can be used to transfer data between memory and I/O devices.
Direct Memory Accessis a method of transferring data between peripherals and memory without using theCPU.
DIRECT MEMORY ACCESS CONTROLLER(DMAC)
DMAC generates address,data and control signals to transfer data between memory and I/O devices.
The DMA controller periodically takes over control of the system bus from the CPU.
DIRECT MEMORY ACCESS
DMA–th I/O controller has the ability to transfer data directly to/from the memory without involving the processor
The I/O DMA controller manages the entire transfer(possibly thousand of bytes in length),arbitrating for the bus
When the DMA transfer is complete,the I/O controller interrupts the process or to let it know that the transfer is complete
The process or initiates the DMA transfer by supplying the I/O device address,the operation to be performed,the memory address destination/source,the number of bytes to transfer
There may be multiple DMA devices in one system
Processor and I/O controllers contend for bus cycles and for memory
For high-band width devices(like disks)interrupt-driven I/O would consume a lot of processor cycles