The Parallel Direct Connection is the second solution to transfer data from one computer to another. The cable
required is slightly more complicated as it has more wires that need to be connected, but the speeds you will get from it will make it well worth the time and effort required to make the cable.
Most people would know the parallel Direct Cables as "Laplink" cables. You get one when you buy the Laplink program or PCAnywhere, it's usually a yellow cable, but you'll be able to make your own by the time you finish reading this page.
Because of the variety of parallel (LPT) ports, four to be precise, but we use the same cable for everyone one of them. We will have a look at them all to make sure we cover everything.
Now, as far as speed's concerned, with a standard LPT port you're looking at around 40 to 60 Kbps whereas with the faster LPT ports you should expect something around one Mbps! Whichever way you see it, it's a huge improvement in comparison to the serial cable (Null modem cable).
Let's have a quick look at the way data is transferred over a parallel link, this will help us understand why it's also a lot faster than the serial method of transfer:
This diagram shows a parallel transfer. In serial transfer there is one block of data moved at a time, whereas with parallel and, more specifically in our example, there are four data blocks moved at a time. Parallel ports transmit data simultaneously over multiple lines and are therefore faster than serial.
If you're having difficulties understanding the diagram just think of a four lane highway, which is our parallel cable, where four cars at a time are moving whereas the serial cable is like a one lane highway with one car at a time moving. Hope that helps.
What does the parallel port (LPT) look like?
With new computers, you will always find the LPT port right above the two COM ports and it's usually color coded purple. No matter what type of LPT port you have, they all look the same, it's the electronic characteristics which changes amongst the for different types of LPT ports and that's transparent to everyone. All LPT ports are female DB-25 connectors.
So what are the different LPT ports?
Because it might seem a bit confusing at the beginning, I have included a bit more technical information on the various ports to help you understand more about them. To keep it simple, I have categorized and color coded them to show which ports match the table above:
4 bit ports
8 bit ports
Laplink cable is used to link two PCs with MSDOS 6.0 or later very effectively by using INTERSVR.EXE (on Host) and INTERLNK.EXE (on GUEST) PCs. But it can also be used to data-transfer at faster speed with DCC Feature of Win9x/Me/2000.
Let's now have a quick look at the pinouts of an LPT port:
The picture below clearly shows the pinouts of the required cable:
One wire should be attached to the metal body of the Male pins on both sides; this is also shown as the "metal body" on the diagram.
Now, because I understand how much trouble someone can fall into when trying to create a cable and get it to work properly, I have included the DirectParallel Connection Monitor Utility, for all the DCC users to troubleshoot and test DCC connection and cable on both computers. It provides detailed information about the connection, the cable being used for the connection, the I/O mode (4-bit, 8-bit, ECP, EPP), the parallel port types, I/O address, and IRQ.
And that pretty much finishes our discussion on Parallel Cable Connections!
Cabling tips for network professionals series
Lesson 1: Network history and fundamentals
Lesson 2: Straight-through UTP cables
Lesson 3: CAT5 UTP crossover cable
Lesson 4: 10Base-T/2/5/F/35 - Ethernet
Lesson 5: 100Base-(T) TX/T4/FX - Ethernet
Lesson 6: Fiber cable
Lesson 7: Direct cable connection
Lesson 8: Serial direct cable connection
Lesson 9: Parallel direct cable connection
Lesson 10: USB direct cable connection
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