Coprocessor I/O When the processor is being used to control I/O and move the data，there is a loss of processor efficiency．[8] Thus the idea naturally arises to use a second processor or coprocessor for I/O．The autonomous coprocessor first appeared in the IBM 709 in 1959，and it performed all the I/O tasks and freed the main processor for its tasks．Fig．1-16 shows a coprocessor connecting an I/O device to the system bus．Control and status information is passed between the processor and the coprocessor by means of paths similar to those of programmed I/O．The processor sends a command to the coprocessor that autonomously performs the 1/O operation．
t9 r+ J! I$ C$ T% F4 m The introduction of a coprocessor makes this configuration a multiprocessor．The problems of any multiprocessor must be addressed with coprocessor I/O．These problems include software synchronization，hardware synchronization，memory protection，and memory coherency．
- }) p9 z$ y; \ N2 P, L/ Z3 U
There are two general types of these coprocessors：programmed I/O channel and direct memory access（DMA）． / K; M7 D/ Q8 n1 E( c
. n0 A3 ~8 r% A
p4 Q' h! J7 q1 i. S I/O devices
* g# l$ W/ r" M' d １）INTERACTIVE INPUT
: P2 }4 {5 s0 l2 L7 Q0 g2 ^$ u The idea of interactive input is to capture information directly into computers and get responses from computers as the input occurs．This happens when you type on a seyboard and immediately see the results of your work on a screen．It is so called as“screen-dependent”．
: R( W) }1 g& e$ V# ?% j* d9 I
Keyboard entry may be too slow or awkward for some jobs，but the keyboard can be bypassed by using one of a number of other interactive devices．Most of today’ s microcomputers，for example，include a mouse or a trackball that lets you use natural arm or hand motions to move the cursor．
7 A7 a' W/ Q2 s; i g5 Q" n
Some screens themselves accept interactive input：The touch screen looks like a normal computer screen，but it can detect the point at which you touch it．
9 p O2 Z N; Y+ x0 T# Q
Technical applications such as graphic arts，mapping，and engineering often require specialized input methods．Perhaps the most natural tools are the light pen and the graphics tablet or digitizer．
& F% s/ m9 K% b2 G( q ２）DIRECT INPUT5 z, D5 U! V* ]
In an information system，the greatest majority of delays，errors，and problems occur during the input phase．To attack the problem，a number of methods have been developed to increase speed，accuracy，and reliability of input．Collectively，these techniques have been referred to as source data automation．Scanning，voice input，and sensor input are three types of direct input．
( l9 e6 c2 f: h# [4 O' QScanners，also called optical scanners，are devices that read printed material so that it can he put in computer- readable form without your having to retype，redraw，reprint，or re-photograph the material．
( N) r7 V0 J% U" a; K+ Z
３）SPEECH RECOGNITION2 w& P$ ]! u$ }
Speech-recognition or voice-input devices accept spoken words through a microphone and change the sounds into computer-readable signals．
9 i+ W. ^; [' ]! Q) C, [& a0 N8 P ４）SENSOR INPUT
- t1 e1 A7 J8 Q/ | Home computer users may link their systems to thermometers，light detectors，and motion detectors to help control energy use and deter vandalism．Input from these detectors is called sensor input．Sensor input is used widely with microcomputers in factories and in scientific and medical laboratories，too．
. | u# v4 y) r! G9 ~) G, j; r ５）DISPLAY OUTPUTS5 w1 x5 D! C4 A4 S2 Q& R5 |
The most common output device is the monitor，a cathode-ray tube（CRT）that is basically a television tube adapted to present text，data，or images generated by computers．High-quality color monitors receive three separate color signals（red，green，and blue）and thus are called RGB color monitors．The clarity or sharpness of the display is termed resolution．The resolution of a monitor indicates the number of image points，or pixels（picture elements），on its screen．
0 ?& l$ u% c/ F
The flat-panel displays used on portable computers are less bulky and require less power than CRT monitors．A common electronic imaging technique used in flat-panel displays is liquid-crystal display（LCD）．Two other flat-panel displays are the gas plasma display，which uses electric current to cause gases to glow，and the electro-luminescent display（ELD），which is similar to gas plasma but has layers of phosphor rather than gas．
1 S" y1 s0 z- x0 U
６）PRINTERS FOR DOCUMENT OUTPUTS
6 N$ ~' i4 _0 V+ d- n. r Document outputs are produced on printers and plotters，devices that produce images or text on paper．These outputs are known as printouts or hard copy．
+ N Z" ]1 B* p6 j+ l3 R% uPrinters and plotters are classified by several criteria，one of them is on impact and non-impact printing methods．
! U1 M0 O- o* {+ b9 t/ A: o
（１）IMPACT PRINTERS
/ a+ S: I8 M9 [! a
A common impact printer for microcomputers is，the dot-matrix printer，which works by striking pins in a print element against the ribbon and paper．The pins are formed into a matrix，and different combinations of pins in the matrix shape the character or image．
/ J( L$ B5 w; x% E6 `
（２）NONIMPACT PRINTERS
/ p/ H1 N" w8 q2 i6 c
Nonimpact printers use heat，laser，or spraying techniques to print characters and images．
" s6 X0 J0 {* I2 \3 ?2 i
The two major nonimpact technologies in use today are ink-jet and laser．
) O( @& T4 `/ d* C 协处理器I/O- ?+ C1 g! a( p
当处理器用于控制I/O和传送数据时，其效率下降。因而自然会想到用第二个处理器或协处理器去处理I/O。1959年在IBM 709机器上第一次使用自主协处理器，由该协处理器完成所有I/O任务，而让主处理器去完成它自己的任务。图1-l6显示了协处理器将I/O没备连接到系统总线的情况。通过类似于程序控制I/O那样的通道，在处理器和协处理器之间传送控制和状态信息。处理器向协处理器发送一个命令，由协处理器自主完成I/O*作。
% u' m" d9 K7 C# O7 t0 S& e# P 采用协处理器使这种配置成为多处理器结构。协处理器I/O也必然会有其他多处理器一样的问题。这些问题包括软件同步、硬件同步、存储器保护和存储器相关等。
) a; Q7 x5 i8 {$ {# x
协处理器有两大类型：程序控制I/O通道和直接存储器存取（DMA）。
4 ]: a+ [7 A" U& S
输入输出设备
: U% C2 s! [4 \0 n( z5 R l）交互性输入- f' F6 \% Q$ C0 K! V5 @2 ?( ^
交互性输入是指当向计算机输入时，获取直接输入计算机的信息，并从计算机得到响应。例如击键时，立即在屏幕上看到击键的结果。所以这又叫做依赖于屏幕型输入。
8 t2 } O$ y( l' p8 k 对于某些任务，键盘输入太慢太笨，可以不用键盘，转而采用很多其他交互性输入设备。例如，目前大多数微型计算机都配有鼠标或跟踪球，让手臂或手的自然运动去移动光标了。
: W2 I5 c. I! @% @# d' t2 T
某些屏幕本身接收交互性输入：触摸屏虽然看上去像普通的计算机屏幕，但可以检测到你触摸的那一点。
% C& c) J4 s4 _$ v, `
诸如图形术、地图绘制和工程之类的技术应用通常需要一些专门的输入方法，使用光笔和图形输入板或数字化仪这几种工具也许是最自然不过的事。
: L9 C# `& Y' K; A: O* o0 x
2）直接输入
" i" g8 ~/ L$ f2 A 在信息系统中，绝大多数延时、错误和问题发生在输入阶段。为解决这一问题，研究出了很多提高输入速度、精确度和可靠性的方法。这些方法可以通称为源数据自动化。扫描、语音输入和传感器输入是3种直接输入类型。
( x8 a1 i( j( Y0 |$ w' p 扫描仪，又称光学扫描仪，是一种用于读取印刷资料的设备，其能使这种资料以计算机可以识别的形式提交，而无须对这些信息再录入、重画、重印或重新照相。
2 l+ }6 i7 g% t: e D, Z 3）语音识别
' H% ~1 q, R0 Q9 @4 Z 语音识别（或话音）输入设备能通过传声器接收口述词语并将其转化为计算机可以识别的信号。
- P o8 \3 `! X 4）传感器输入
& {" o8 R% T+ R# ?; s: `9 O 家庭电脑用户可将他们的计算机系统与温度计、光探测器和运动探测器连接起来，以便控制能源的消耗和防止非法入侵。这些探测器输入的信息称为传感器输入，传感器输入也广泛用于工厂和科研、医疗部门的微型计算机上。
2 X7 x0 f* ]4 f# Q, G
5）显示输出$ q6 T6 Y6 D9 _- C2 y0 s1 j
最常用的输出设备要算监视器了，它是与电视机显像管基本相同的阴极射线管（CRT），经改制以适应显示由计算机产生的文本、数据或图像。高性能彩色监视器接收3种不同颜色的信号（红、绿或蓝），因而称之为RGB彩色监视器。监视器的清晰度，其术语叫做分辨率。监视器的分辨率指明屏幕上的图像点或像素（图像元素）的数量。
/ y& M6 V! S( `' y
用于便携式计算机上的平面监视器比CRT监视器体积小，耗电少。用于平面监视器的一种常用电子显像技术是液晶显示（LCD）。另外两种平面监视器是气体等离子监视器和电致发光监视器（ELD），前者用电流使气体发出辉光，后者与气体等离子体相似，但激发的是若干磷光体层而不是气体。
7 Z# F8 ~3 N" a
6）文本打印机$ ^0 ]* D2 }# }2 C5 z( K
文本是在打印机和绘图仪上输出的，这两种设备在纸上产生图像或文本。这种输出称为打印输出或硬复制。
+ v/ H+ e' J5 O3 k5 Q4 v. [3 U# g
打印机和绘图仪可按好几种方式分类，其中之一是按接触式或非接触式打印来分类。
; o. r- b' F! S3 L; O, E （1）接触式打印机。
% u/ R$ y3 O5 Q& g; ^ 微型计算机上常用的接触式打印机是点阵式打印机，其通过驱动装在打印头上的打印针对着色带和纸击打。多针构成一个阵列，阵列中针的不同组合形成了字符或图像。
" k4 c/ K4 s/ o8 v- t; n; ?
（2）非接触式打印机。
+ [+ {" s2 v6 z3 T9 ^! {6 k 非接触式打印机采用热、激光或喷墨技术来打印字符和图像。目前使用的非接触式打印技术主要有两种：喷墨和激光。
