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Keyboard/Monitor, Disk Drive
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External Devices, ▪I/O operations are accomplished through a wide, collection of external devices ., ▪that provide a means of exchanging data between, the external environment and the computer., ▪An external device attaches to the computer by a, link to an I/O module
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External Devices, ▪The link is used to exchange control, status, and data, between the I/O module and the externaldevice, , ▪An external device connected to an I/O module is often, referred to as a, peripheral device or, simply, a peripheral
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External Devices, ▪ External devices can be classified into three categories:, • Human readable: Suitable for communicating with the computer, , user ,ex : monitor, printer, • Machine readable: Suitable for communicating with equipment, , ex: magnetic disk, sensor, • Communication:, , • Suitable for communicating with remote, , devices, ex: modem
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Structure, , ▪The interface to the I/O module is in the form of, control, data, and status signals., ▪Control signals determine the function that the device will, perform, such as send data to the I/O module (INPUT or, READ), accept data from the I/O module(OUTPUT, or WRITE), report status, or perform some control, function particular to the device (e.g., position a disk, head).
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Structure, ▪ Data are in the form of a set of bits to be sent to or, received from the I/O module., ▪ Status signals indicate the state of the device., ▪ Examples are READY/NOT-READY to show whether, the device is ready for data transfer.
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Structure, ▪Control logic associated with the device controls, the device’s, operation in response to direction from the I/O, module., ▪The transducer converts data from electrical to, other forms of energy during output and from, other forms to electrical during input., ▪Typically, a buffer is associated with the, transducer to temporarily hold data being, transferred between the I/O module and the, external environment
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Keyboard/Monitor, ▪The most common means of computer/user interaction is, , a keyboard/monitor arrangement., ▪ The user provides input through the keyboard., ▪This input is then transmitted to the computer and may also, be displayed on the monitor., ▪ In addition,the monitor displays data provided by the, computer., , ▪The basic unit of exchange is the character., ▪Associated with each character is a 7 or 8bits lengthcode.
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Keyboard/Monitor, , ▪The most commonly used text code is the International, Reference Alphabet(IRA)., , ▪ Each character in this code is represented by a unique 7-bit, binary code, ▪ 128 different characters can be represented., , ▪Characters are of two types: printable andcontrol., ▪Printable characters are the alphabetic, numeric, and special, characters that can be printed on paper or displayed on a, screen., ▪Control characters :controlling the printing or, displaying of characters; ex carriage return.
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Working, ▪For keyboard input, when the user depresses a key, this, generates an electronic signal that is interpreted by the, transducer in the keyboard and translated into the bit, pattern of the corresponding IRA code., ▪This bit pattern is then transmitted to the I/O, module in the computer.
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Working, ▪ At the computer, the text can be stored in the sameIRA code., ▪On output, IRA code characters are transmitted to an external, device from the I/O module., , ▪The transducer at the device interprets this code and sends the, required electronic signals to the output device either to display the, indicated character or perform the requested controlfunction.
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Disk, Drive, ▪A disk drive is adevice implementing, a disk storage mechanism., ▪A disk drive contains electronics for exchanging data, control,, and status signals with an I/O module plus the, electronics for controlling the, disk read/write mechanism., , ▪In a fixed-head disk, the transducer is, capable of converting between the, magnetic patterns on the moving disk, surface and bits in the device’s buffer, ▪A moving-head disk must also be able to cause the disk, arm to move radially in and out across the disk’s surface
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THANKS……..
