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History, evolution and types of parallel ports
History
In 1981, IBM (International Business Machines) introduced the Personal Computer (PC). The parallel port (Standart Parallel Port SPP) was including in the first PC and it was added to this one like an alternative to the low yield of the serial port, to use it like controller of the dot matrix printers of high performance. This port had the capacity to transmit 8 bits of data simultaneously (of the PC to the printer), whereas the serial port did one by one. At the moment that the parallel port was presented/displayed, the point printers were the main external device that I connect myself to this one. When becoming extensively used, the parallel port got to be the answer to connect faster devices.
After this beginning, three great groups of problems appeared to the usuary developers and of this port: First, although this one had increased its speed considerably, there was change in the architecture or no performance. The Maxima speed of attainable transference kbyte /seg was in favor of the 150. and it was extremely software.intensive. Second, there was no a standard for the electrical interface. This caused many problems when it was wanted to guarantee the operation in multiple platforms. Finally, the design form that they gave him, limited the distance of external cables until a maximum of 1.8 meters. In 1991 there was a meeting of manufacturers so that a new standard for the intelligent control of printers through a network could be developed. These manufacturers, where they were including Lexmark, IBM, Texas Instruments and others, formed Network Printing Alliance (NPA), like an answer to these necessities.
From the introduction from the PC to the market, the parallel port has undergone several modifications to make it faster. Since the original port was unidirectional, the bidirectional port was created. The bidirectional port was introduced with the compatible PS/2. This it allows a communication of 8 bits in both directions. Something interesting to notice is that the original port had the possibility of being bidirectional making a connection between two pins of an electronic component that came including in this one. (In other words, the original port is bidirectional in basic design, but not in the operational design). Finally Enhanced Parallel Port (EPP) and Extended Capability Port have been created (ECP). These two last ones are to the standard port like the Pentium to the 286, in addition to being bidirectional.
Initially the parallel port was used for the communication with printers. At the moment it is used also to handle other peripheral like CD ROM, tapes of backup copy, hard disks, network cards, copy protectors, scanners, etc.
In the present time there are four types of parallel ports:
Standard parallel port (Standart Parallel Port SPP)
Parallel port PS/2 (bidirectional)
Enhanced Parallel Port (EPP)
Extended Capability Port (ECP)
In the following table is information synthesized of each one of these types of ports.
SPP | PS/2 | EPP | ECP | |
Date of Introduction | 1981 | 1987 | 1994 | 1994 |
Manufacturer | IBM | IBM | Intel, Xircom and Zenith Data Systems | Hewlett Packard and Microsoft |
Bidirectional | No | If | If | If |
DMA | No | No | No | If |
Speed | 150 Kbyte/seg. | 150 Kbytes/seg. | 2 Mbytes/seg. | 2 Mbytes/seg. |
Questions? pparalelo@hotmail.com
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