Parallel port what it is and what it is for

Everyone with a computer or computer equipment should have heard of the parallel port and the serial port at some time. In this article we will extend the operation and use of the first, although it is actually extinct due to lower performance and compatibility. What type do you think is the IDE or PATA port of HDDs, and USB? Well now we will see.

Index of contents

What is the parallel port

The parallel port is a type of interface present in computers and other computer and electronic equipment that allows us to connect different types of peripherals. This communication interface is carried out through different types of ports, with a certain number of contacts or cables.

The name it receives is due to its operation, which is done by sending a series of bits at a time and in the form of packets. If we take this to a physical level, what we would have is a cable for each bit that is sent, thus forming the data bus. For example, if we wanted to send 8 bits at a time, we would need an 8-wire bus. In addition, a series of control bits are used that will travel in both directions on separate tracks in order to synchronize the connection between the peripheral and the host, and also ground cables.

Also through the type of connector we can deduce that it is a parallel port interface, since they are usually connectors of considerable size and with a multitude of pins arranged in a horizontal or vertical line.

Parallel port source: Centronics

Centronics is arguably the most representative parallel port and until recently could be found on personal computer motherboards, but far from the only one.

DB25

The beginnings were indeed in the printers and the need to transfer ASCII code to the device so that the print head would print the character in question. When a serial port was used, the bits were sent one by one and the printer had to wait for the complete code to join them again. So a way was created to pass the entire ASCII code using 8 bidirectional pins, along with others for control and ground. Due to its relationship with the Centronics printer, the port was renamed by the same name, launching in 1970.

The parallel port was developed together with the DOS and Unix operating systems, the main ones of that time, and still today in their internal code they name the parallel ports in the same way.

In the case of DOS systems they are called LPT1, LPT2, etc. meaning Line Print Terminal. And in the case of Unix, they were called, and they are called / dev / lp0, lp1, etc.

Subsequent implementations

In addition to the Centronics port, major manufacturers were rolling out new, higher-speed versions due to the evolution of peripherals.

DB25

DB25 pins

Later IBM did the same with its series of printers, although in this case the connector happened to have no less than 36 pins, being called DB25. A port that the manufacturer tried to use for other peripherals, although without much success, reaching a speed of between 40 and 60 KB / s.

Bi-tronics

In 1992 HP invented the Bi-Tronics system for its LaserJet 4, an interface that increased the capacity of previous parallel connectors.

EPP and ECP

EPP port on ISA card

Later, higher capacity ports would appear, such as the EPP (Enhanced Pasrallel Port), which operated almost at the speed of the ISA bus. This had a great impact for being used in network adapters, external storage units or scanners. Its speed could reach 2 MB / s. Then Microsft developed the ECP (Extended Capability Port), a port designed to be used in high performance printers.

Until finally the interface was standardized by means of the IEEE 1284 norm. The capacity was extended with cables that allowed connecting up to 8 devices. And so its use expanded more and more until it reached Zip storage units , hard drives, printers, and other devices continued to use it.

Newer PC parallel port types

These are the few ports that have remained in effect years ago on personal computers. Everything else is already a serial port.

SDI

IDE bus

It stands for Integrated Drive Electronics, and it's really not the interface but the name of the cable it was extended with. The interface is called ATA, P-ATA or PATA (Parallel Advanced Technologies Attachment), it is a standard of connection interfaces for mass storage devices and optical and magnetic disk readers. ATA is the derivative of the full name of the ATAPI standard.

This interface was developed by Western Digital, and obviously the first teams that implemented it were the IBM, and later in the Dell and Commodore. Control of the interface was initially carried out by a dedicated chip, which would then be integrated into the chipset or south bridge of the boards. This was done thanks to the DMA (Direct Memory Access) technology that allowed access to the system memory without depending on the CPU, so it was another chip that was in charge of tasks that were releasing the CPU load.

This interface in its first versions had cables with 40 connectors, but with the appearance of the UDMA / 66 mode the number was doubled to no less than 80. The introduction of these 40 cables was not to carry more data, but they had the function of ground, thus reducing the effects of capacitive coupling between neighboring cables.

In this way we can find all these versions until the appearance of the Serial ATA ports:

Version	Speed	Commentary
ATA-1	8 MB / s	First version
ATA-2	16 MB / s	Add block transfer and DMA support
ATA-3	16 MB / s	Review of the previous
ATA-4	33 MB / s	It is called UDMA or Ultra DMA
ATA-5	66 MB / s	Or Ultra ATA-66 lowers the 90 ns latency barrier, staying at 60 ns.
ATA-6	100 MB / s	Or Ultra ATA-100 with a latency of 40 ns
ATA-7	133 MB / s	Or Ultra ATA-133 with a latency of 30 ns
ATA-8	166 MB / S	Or Ultra ATA-167 with a latency of 24 ns

Regarding the bus, it supports a total of two connected devices at the same time, one of them must be as a master and the other as a slave, since the controller must know how to identify which unit is the one that should receive the data at all times. This configuration will be done through a panel of jumpers that include the storage units and CD / DVD players.

PATA jumper settings

• Master: it will always have the device that has the operating system installed, something less is recommended. If there is only one unit connected, it must be a master. The pins to the left will be bridged. Slave: You always need a master to be able to function. The jumper will be removed to remain as a slave. Cable select: it is a function where the controller chooses which is master and which slave. The unit that is furthest from the cable will always be the master, while the one that connects to the central bus will be the slave. Capacity Limit - There is always another bridge with the ability to limit the drive's storage capacity to 40GB.

Currently this interface is no longer used as it has been completely replaced by the Serial ATA or SATA bus .

SCSI

SCSI port

The other connector with the greatest impact in this case more oriented to workstations and disk array is the SCSI bus (Small Computer System Interface). It is a parallel data transfer technology similar to PATA but less widespread than the previous one in general consumer equipment due to its higher cost of implementation.

It appeared in 1990, and it is still possible to see this type of system in servers or old Macintosh computers, high-performance computers and with high storage capacity to get to where the IDE was not capable, not speed, but capable of connecting units.

These are the versions of SCSI until its replacement by Serial Attached SCSI (SAS), its serial version:

Version	Speed	Commentary
SCSI 1	5 MB / s	It is an 8-bit bus with a 50-pin Centronics-type connector. Supports a maximum length of 6m and up to 8 connected devices
SCSI 2	Fast: 10 MB / S	An 8-bit bus with a 50-pin connector. Supports 3m length and up to 8 connected units
Wide: 10 MB / S	The bus doubles to 16 bits with its 68-pin connector. Supports a length of 3m and up to 16 connected devices
SCSI 3.1, SPI or Ultra SCSI	Ultra: 20MB / s	34-pin 16-bit connector and a maximum of 1.5 m. Supports 15 devices.
Ultra Wide: 40MB / s	68-pin 16-bit connector and a maximum of 1.5 m. Supports 15 devices.
Ultra 2: 80MB / s	68-pin 16-bit connector with a maximum length of 12 m. Supports 15 devices.

SCSI HDD

From SCSI 3.2 the interface started to operate on a serial bus, the following versions being 3.2 called FireWire, 3.2 called SSA and 3.4 called FC-AL, which would not have a place in this article.

An ideal interface for creating large RAID volumes on multiple levels. It does not need a drive configuration jumper and it was not compatible with PATA until the arrival of SAS on its part and SATA on the other.

Differences with the serial port

Serial - parallel converter

The big difference from the parallel port is that serial ports send two data as a serial bitstream, one behind the other over the same cable. The serial port standard is RS-232, one of the most widely used connectors in older equipment for connecting peripherals. that was replaced by the USB port mainly in Europe, while FireWire was extended in America by its use in Apple Macitosh.

In 1987, with the entry of IBM PCs, one of the first bidirectional serial ports was created, the PS / 2, an 8-bit port that can still be used today with old mice and keyboards, delivering a speed of between 80 and 300 KB / s, determining the arrival of serial ports for peripherals. Later the USB 1.0, 1.1, 2.0, etc would appear.

Conclusions on the parallel port

Currently the serial port is fully used for all peripheral and bus applications. This interface needs much less cables, making it more portable. It also allows the transport of energy to power devices, specifically from USB 2.0.

The equipment we currently have does not have parallel connections, and in them we can see high-speed USB ports, HDMI video ports , DisplayPort, DVI or AG P, and internal storage buses such as PCI or SATA. In them we have speeds of up to 2 GB / s in each PCI-Express version 4.0 lane .

If you want to continue with us, we recommend a few interesting tutorials:

Have you ever used IDE or SCSI? If you have questions about the subject, you can always ask us in the comment box. We hope you found it useful.