Parts Of a Computer parts of a computer

The first thing is the I / O needs unity, to see what the printer at the moment. The program that the pressure has gone and asked for time has no idea if the printer can print, or even if a printer! Or care - until I / O unit to clarify.

The I / O sends a request to the printer status via activation of a line of application on the output cable. Field lines of data or data that identifies them as a question of status. Provided there isa printer there, and it is switched on (can be switched off for maintenance), it activates the signal received a response on the basis of the printer.

Maybe the printer paper, or the operator is replacing the band. Most of the time the printer waits passively for a job or printing a previous job, that the I / O management. The logic of the printer determines this state, because some flip-flop is set, as it passes through its activities will be. TheseThe conditions are the input wires through the command line application was received by the gated I / O unit.

For example, a switch to turn on the printer when the paper runs out. This sentence is a flip-flop "No Paper". A signal from the signal 'request was generated' status from I / O allows the signal of 'Paper Out', on cable input data are gated as one of "data bits". The state is the I / O through an entrance, triggered by the generatedrequest for initial state.

The "no paper" po ', along with all other status bits, a status register, where it can be verified by the CPU are gated. A message from the operating system can be sent to the operator to inform him of the situation, if they need an intervention by the operator.

Assuming that everything went well for the printer, we can begin to send data. A typical line printer print 160 columns across the page, so we need to transfer data at 160 characters. Depending on the wordDimensions in this system, we are the first 4 to transmit, for example in the log buffer in the printer. Change the control signal, the request may be, and the data port to the output cable. A similar process of logical printer ports these 4 characters in the right position in the buffer. Since the buffer is full, the other 4 characters are desired. I / O, after updating its data and address are registered, it sends the next 4

This process continues until the print buffer is full,what a line for printing. The print command is given, and the hammers to strike the print ribbon to paper as the correct character goes under the hammer. On a drum printer, for example, the characters are arranged in staggered rows of 160 of each character drum. When a series of "A" is under the hammer, a hammer is activated whenever you receive "A character" in the buffer corresponding print. A revolution of the drum enables the entire line will be printed.

The paperalong a series of space and the next row can be moved will be printed. While the paper is required, is sent to be printed in the next line of characters. There are a lot of time for this predictable, since the data are transmitted electronically, in microseconds, while paper is moved mechanically, in milliseconds millisecond = 1000 microseconds ().

This printing process is completed, the buffer I / O is a zero, and returns the operating system that has completed the task. This isdone by an interrupt to the operating system displays a status word in the work area reserved completed successfully. If there is a problem with the work of I / O that goes from the printer in the status word is to get the operating system writes.

The operating system can now share the next print job to the printer as before the handshake, everything that has happened and what needs to happen would be informed.

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