| 36-pin Centronics connector on a printer |
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Early personal computer printers used an RS232 serial interface. These printers were essentially teleprinters without a keyboard; they could receive and print but could not transmit. They migrated to personal computers from the mainframe world. The connector was usually a 25-pin D-sub connector. The serial port is described in the chapter on serial ports.
In the early 1970s, Centronics developed a low-cost printer. This was a dot-matrix printer with a parallel interface. The parallel interface was less expensive to produce than the serial interface that was standard at the time. The Centronics parallel printer interface, later standardized as IEEE 1284, became the standard printer interface for early personal computers.
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The standard parallel interface is described in the chapter on the Parallel Port.
Before personal computer networks became commonplace, users often connected printers to switch boxes that connected a single printer to several computers. Some of these printer switches were operated manually while others automatically sensed when a computer needed the printer and switched accordingly. Some had printer buffers that could store one printer's print job while another computer used the printer.
Most printers for personal computers now use the USB interface described in the chapter on the Universal Serial Bus.
In the early days of personal computer networking, printers could be used over a network if attached to a print server. A print server is any computer with a printer attached and shares that printer over the network. Some print servers were self-contained modules.
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Printers with embedded print server software (essentially a built-in computer that shares the printer) have an Ethernet port to connect to the network. The print server and port may be a plug-in module.
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As a network computer, a built-in or self-contained print server is configured with all the necessary network parameters (IP address, subnet mask, etc.). A printer's built-in print server may be configured via the front panel on the printer. Self-contained print servers were often configured using a built-in web server that presented a web page with which the user could interact.
Most modern printers connect to a network using WiFi. A printer's WiFi interface is configured like any computer's WiFi interface.
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Early printers worked only in real time; they printed each character as presented on the printer port. Since early operating systems were not multitasking, the computer could do nothing else while printing.
Print buffers that stored print jobs while they printed them were soon developed. These were connected between the computer and the printer. The print buffer quickly received and stored the print job, making the computer available for other tasks.
Only the earliest printers lacked internal print buffers; even some could buffer a single line of characters. Operating systems also soon came with print management software that buffered print jobs in the computer if necessary. Modern printers can hold many print jobs in their print buffers and communicate with computers so users can easily manage the buffers.
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