编程和中断启动的I / O之间的区别

先决条件– I / O接口(中断和DMA模式)
CPU和I / O设备之间的数据传输可以采用多种模式进行。这是三种可能的模式：

1. 编程的I / O
2. 中断启动的I / O
3. 直接内存访问(DMA)

在本文中，我们将仅讨论前两种模式。

1.编程的I / O：
在这种模式下，数据传输由计算机程序中编写的指令启动。需要输入指令将数据从设备存储到CPU，并且需要存储指令将数据从CPU传输到设备。通过此模式进行的数据传输需要CPU不断监视外围设备，并且一旦传输开始就监视新传输的可能性。因此，CPU保持循环状态，直到I / O设备指示它准备好进行数据传输为止。因此，编程的I / O是一个耗时的过程，它会使处理器不必要地保持繁忙，并导致CPU周期的浪费。
这可以通过使用中断工具来克服。这构成了中断启动的I / O的基础。

2.中断启动的I / O：
当数据可用并且接口准备好进行数据传输时，此模式使用中断工具和特殊命令来通知接口发出中断命令。同时，CPU继续执行其他任务，无需检查该标志。设置标志后，将通知接口并启动中断。该中断导致CPU偏离其对I / O传输的响应。 CPU通过将来自程序计数器(PC)的返回地址存储到存储器堆栈中来响应该信号，然后跳转到处理I / O请求的服务。传输完成后，CPU返回到它正在执行的上一个任务。服务的分支地址可以通过两种方式选择，即向量中断和非向量中断。在向量中断中，中断源将分支信息提供给CPU，而在非向量中断的情况下，分支地址被分配到内存中的固定位置。

编程和中断启动的I / O之间的区别：

Programmed I/O	Interrupt Initiated I/O
Data transfer is initiated by the means of instructions stored in the computer program. Whenever there is a request for I/O transfer the instructions are executed from the program.	The I/O transfer is initiated by the interrupt command issued to the CPU.
The CPU stays in the loop to know if the device is ready for transfer and has to continuously monitor the peripheral device.	There is no need for the CPU to stay in the loop as the interrupt command interrupts the CPU when the device is ready for data transfer.
This leads to the wastage of CPU cycles as CPU remains busy needlessly and thus the efficiency of system gets reduced.	The CPU cycles are not wasted as CPU continues with other work during this time and hence this method is more efficient.
CPU cannot do any work until the transfer is complete as it has to stay in the loop to continuously monitor the peripheral device.	CPU can do any other work until it is interrupted by the command indicating the readiness of device for data transfer
Its module is treated as a slow module.	Its module is faster than programmed I/O module.
It is quite easy to program and understand.	It can be tricky and complicated to understand if one uses low level language.
The performance of the system is severely degraded.	The performance of the system is enhanced to some extent.