The parallel port technology history is an important part of personal computing. Before USB became the standard way to connect peripherals, parallel ports were widely used to connect computers with printers and other external devices. Their ability to transfer several bits simultaneously made them useful for fast communication with peripherals during the early development of personal computers.
From the introduction of printer interfaces in the 1970s to the standardization of IEEE 1284 and the eventual rise of USB, parallel ports went through several important stages. Understanding this history provides a useful look at how computer connectivity evolved.
The Origins of Parallel Ports
The origins of parallel ports can be traced to the 1970s and the development of printer interfaces by Centronics. The company introduced a parallel interface for its printers that could transfer multiple bits at the same time.
Unlike a serial connection, which sends data one bit after another, a parallel connection uses multiple data lines. An early parallel printer interface commonly transferred eight bits simultaneously, making it well suited to computer-to-printer communication.
The technology became increasingly popular as dot-matrix printers and personal computers became more common.
Parallel Ports and the IBM PC
A major development in the parallel port technology history occurred in 1981 with the introduction of the original IBM PC.
IBM included a parallel printer interface based on the Centronics design. On the computer side, IBM commonly used a 25-pin D-sub connector, while printers generally used a larger 36-pin Centronics connector.
The interface became associated with the term LPT, short for Line Printer. LPT1 was commonly used as the first parallel-port designation on PCs.
This helped make parallel printer connections a familiar part of personal computing.
How Parallel Ports Worked
Traditional parallel ports used several groups of electrical lines for communication. The most important were the data lines, status lines, and control lines.
The eight primary data lines allowed a byte to be transmitted at once. Control and status signals were used to coordinate communication between the computer and peripheral.
This communication method was particularly useful for printers because the computer could send character and formatting information while the printer used status signals to indicate whether it was ready to receive more data.
Parallel Ports Become More Versatile
Although parallel ports were initially designed mainly for printers, their capabilities eventually expanded.
Manufacturers began developing devices that could use the parallel interface for purposes other than printing. Some scanners, external storage devices, networking accessories, and specialized hardware used parallel connections.
This increased flexibility also exposed a problem: different manufacturers sometimes implemented parallel communication differently. A standardized approach was needed to improve compatibility and performance.
The Development of Bidirectional Communication
Early parallel interfaces were primarily designed around communication from the computer to a printer. Later versions introduced better support for communication in both directions.
Bidirectional operation allowed peripherals to send information back to the computer. This was important for devices that needed to exchange larger amounts of information rather than simply receive printer data.
These developments helped transform the parallel port from a relatively simple printer connection into a more general-purpose peripheral interface.
EPP and ECP Modes
Two important developments were Enhanced Parallel Port (EPP) and Extended Capability Port (ECP).
EPP was designed to provide faster communication with peripherals and was useful for devices that required more interactive data transfer.
ECP introduced additional capabilities and was particularly useful for high-speed peripheral communication. These modes helped extend the useful life of parallel-port technology as computer peripherals became more sophisticated.
IEEE 1284 Standard
One of the most important milestones in the parallel port technology history was the introduction of IEEE 1284 in 1994.
The IEEE 1284 standard established specifications for parallel communication between computers and peripherals. It defined several operating modes and helped improve compatibility between hardware from different manufacturers.
The standard included traditional compatibility operation as well as more advanced modes such as EPP and ECP.
IEEE 1284 therefore represented an important attempt to bring greater consistency to a technology that had previously developed through several manufacturer-specific implementations.
Parallel Ports Beyond Printers
During their peak popularity, parallel ports were used for more than conventional printers.
Some external storage products used parallel connections because computers already had the interface available. Other examples included scanners, removable drives, network adapters, and specialized industrial equipment.
Parallel ports also became popular among hobbyists and hardware developers because individual pins could be accessed directly for controlling or communicating with external electronics.
This made the interface useful for experimentation and simple hardware projects.
Why Parallel Ports Declined
Despite their usefulness, parallel ports eventually faced strong competition from newer technologies.
USB offered several advantages. It required fewer physical connections, supported a wide range of devices, and made connecting and disconnecting peripherals easier. USB also provided a more flexible architecture for modern computers.
Network technologies also reduced the importance of direct printer connections. Printers could increasingly communicate with computers over Ethernet and, later, wireless networks.
As a result, computer manufacturers gradually stopped including traditional parallel ports.
Parallel Ports in Modern Systems
Traditional parallel ports are now considered legacy interfaces. Most modern desktop and laptop computers do not include them as standard equipment.
However, parallel ports have not completely disappeared. They can still be encountered in older computers, industrial machines, laboratory equipment, manufacturing systems, and specialized hardware.
Adapters and expansion cards can also provide parallel-port connectivity when older equipment needs to be connected to a newer computer.
Parallel Port vs. USB
The transition from parallel ports to USB represents a broader change in computer hardware design.
| Feature | Parallel Port | USB |
|---|---|---|
| Original major use | Printers | Many peripherals |
| Data communication | Multiple lines simultaneously | Serial communication |
| Common PC connector | DB-25 | Various USB connectors |
| Bidirectional support | Added in later standards | Built into the design |
| Hot swapping | Limited | Supported |
| Modern popularity | Mostly legacy | Widely used |
USB eventually became the more common solution for connecting peripherals because of its flexibility and ease of use.
The Legacy of Parallel Port Technology
The parallel port technology history demonstrates how computer interfaces evolve when new requirements emerge. The technology began as a practical way to connect computers to printers and later developed faster and bidirectional communication modes.
Although parallel ports have largely disappeared from consumer computers, they played an important role in the development of personal computing. Their legacy can still be seen in older hardware and specialized systems that continue to depend on them.
The move from parallel ports to USB and network connectivity also illustrates a broader trend in technology: interfaces tend to disappear from everyday use when newer standards offer greater flexibility, convenience, and compatibility.
Conclusion
The history of parallel ports spans several decades of computer development. Starting with printer interfaces in the 1970s, the technology became widely associated with IBM-compatible PCs during the 1980s and gained additional capabilities through bidirectional communication, EPP, ECP, and IEEE 1284 standardization.
Although USB and network technologies eventually replaced parallel ports in most modern computers, the interface remains an important part of computing history. It helped establish a common method for connecting PCs with printers and other peripherals during an important period in the evolution of personal computers.
