I work with a number of true Road Warriors. These are the guys (mostly) that travel enough to claim Executive Frequent Flyer status. While just about every management person I know in World Wide Widgets has a desk top personal computer, these guys use laptop computers exclusively. They are on the road so much that they need to have their stuff available both at home and on the road. In their office, their laptops slip into a docking station, which sprouts a keyboard, monitor, sometimes its own disk, and connections to the company LAN, printers, and communications. But the heart of the system is still the same laptop that they carried to Siberia or West Virginia last week.
Last December I wrote about my experiences in purchasing a personal laptop for my Bonnie to use (see www.icehouse.net/demattia). We finally have one, and no, it was not the IBM Thinkpad that I had expected to get, but one with a more Asian brandname. Long story, wrong place. Anyhow, as I mentioned in that story, there are some significant differences between the $5000 Grand Prix laptops that have docking stations, active matrix screens, and 64MB memory banks, and the $2000 jogging path unit that we bought. Starting with, we don't have a docking station.
And our needs are different, too. This is not our only computer, since I have my desktop in my office, and the laptop is for Bonnie to use in her business, and maybe for us to take with us on a trip to the lake to stay in touch with the world. I already had a printer, a black and white Laserjet. With this system, we also bought a color printer, an HP Deskjet. She has no need to access my printer (since hers prints black and white as easily as it prints color), but I would like to use hers, from time to time (since mine does not do color).
And, we would like to somehow share data. One can always use sneakernet, and carry a floppy back and forth between the two systems, but this gets awkward when you have a file that is larger than what will fit on one floppy.
The perfect answer for all these problems would be to use a network. Chris Finley and others have written quite a bit in these pages on how to install a peer to peer network in a small office or home office environment. But we cannot always guarantee that the laptop will be there all the time -- after all, it is designed to be portable. And when the laptop goes away, you lose the use of the printer that is attached to it, if the two computers are networked. And, while network cards and wires and such are not real expensive, it is just one more silly thing to have to worry about and work with. So I decided to solve these problems with pre-network technology.
And I decided to solve these problems separately. I was surprised that there were no simple, off the shelf answers for these problems, since more and more people surely have this situation of a laptop and a home computer wanting to share a common device.
The first problem, that of dual access to the new color printer from two PCs, can be dealt with by using a DB25 AB Switch box. I ran a straight through 25 pin Male / Male cable from the printer port on my desktop computer to one plug on this box, and another similar cable from the printer port on the laptop to the box, and then a DB25 / Centronix cable to the printer from the output port of the box. By throwing a big switch (labeled A and B) on the box I can connect either computer to the printer. Total cost was $20 for the box, and about $10 apiece for the Male / Male cables. I already had the Centronix cable for the printer.
Perhaps at this point I should talk a little about cables. The plugs in the back of a typical PC computer consists of various flavors of male (pins out) and female (holes) plugs. There are all sorts and varieties, to allow you to connect modems, VGA monitors, joysticks, and serial and parallel communications cables, and to just cause general confusion when you are setting things up. Generally the communications plugs are sort of "D" shaped connectors arranged with two rows of pins or holes, with either 9 or 25 pins available.
The DB9 ports, and the male DB25 ports, are usually for serial communications lines, like for mouses and modems. The line printer port is usually a female DB25 port. What is kind of interesting about this, is the printer side of this is a 36 pin male Centronix plug. Somewhere along the wire, 25 pins on one end generate 36 pins on the other. I really do not know or particularly care why this is, since it all seems to work. (In fact, I later learned that it only uses 17 of the 25 (or 36) pins!).
When I first started in this business, computers that had printers were rare, because printers cost so much. And part of the reason was the interface from the printer to the computer. These were usually very specialized and very large circuit boards were designed expressly for a specific printer and a specific computer. In the early 70's, we bought our first computer that came with a then new Centronix printer, and its now famous Centronix interface. The Centronix printer was a desk top device that had a then unique multi pin print head that scanned over the paper and formed the characters as it wiped the paper. I believe it printed 165 characters / second. And of course it connected to your computer with this simple little plug. It was quite revolutionary for the times, dropped printer prices by almost an order of magnitude, and for a while they literally owned the printer market for minicomputers. And I haven't a clue if the company still exists anywhere; I have not heard of them as a printer company for a long time, even though their interface lives on to this day, and I can't find any evidence of them on the Web. Why IBM decided to use a DB25 plug on the original IBM PC rather than a female Centronix plug escapes me, but it was probably a cost saver.
So, if you now look at the cord connecting your existing printer, no matter what kind it is, to your IBM clone computer (Macs are different, of course) you will see that it is DB25 male on one end, and a funny plug with a bar in the center (the female Centronix plug) on the other end.
To connect multiple printers to one computer, or multiple computers to one printer, you either need to connect and disconnect a lot of cables, or get a switch box -- something that lets you plug your two similar things in one end, so that the signal can be switched between them, and go out to the other thing on the other end. And these things invariably have all DB25 female plugs on them, which means that all the cables connecting to the box must have a DB25 male end on them.
Lucky us, the printer cable came that way. So, presuming that you want two computers to talk to one printer (such as was my case), you then have to find two more cables, with a full set of 25 untwisted lines in them (that is, Not a null modem arrangement), with DB25 male ends on each end. And stores all over Spokane have all these cables by the rack.
What is tough to find is the switch box. I only found these boxes in a few of the several stores I looked at. I found electronic switch boxes that ran from $25 to $85. I really could not see the difference between them, so I of course bought the $25 box. And when I got it home, found that it would not transmit the printer signals back to the computer. (Yes, I know, the $85 box probably would have). So, I switched to the manual box, at $20. And that works just fine.
You may note that my desktop printer still has a problem, in that its printer port is tied up to this switch box, to allow it to print to the new color printer. What about my Laserjet? I could have added another switch box and a couple more cables, but I solved that problem for another $14 by adding a second printer port to my desktop computer, and connecting the Laserjet to it. It turns out that a personal computer will support at least three printer ports. And while the addresses must be different, for some reason the IRQ numbers can all be the same, because the printer drivers appear not to use interrupts. I don't understand why not, but it all works.
So, my final problem was to find a way to send files back and forth between the two computers. The Laptop came bundled with a boatload of software, including something called Laplink. This product has been around for several years, and was first developed to use two computers' serial ports to send data to each other at the quite incredible speed of 115K bits per second. They have enhanced the product to use several other types of devices, like networks, Irda ports, and the parallel port.
Irda ports seem like a neat idea. These things come bundled in just about every laptop sold now a days, and can transmit information at 115Kpbs, 1Mbps, or 4Mbps using infrared pulses, just like your TV clicker uses to change the channels, except at a somewhat more rapid rate. They are a great little idea. The only problem is, your desktop probably did not come with one of these devices. I looked all over town to find one, and only came up with one location that did sell them (or even heard of them), and those people did not have a clue how to make it work. I searched the back issues of several computer magazines (using the internet, of course) and it appears that this device plugs into one of your serial ports. But it is difficult to tell, because of about 120 articles talking about them, 119 were about the laptop end, and only one talked about the desktop end. And the outside of the box in the store gave out no useful information, and I did not want to rip the box apart in the store just to get to the instruction book. It seems like a great idea, but maybe one whose time has not yet come. I did not want to risk $50 to just give it a whirl.
So, I decided to use my parallel ports, which Laplink said they would support. I proceeded to connect my printer ports together with my printer cables, and fired up the Laplink programs on both computers, and got squat response.
Laplink is supposed to present a dual file manager type screen on your computer, with one screen being files on your computer, and the other screen being the files on the remote computer. The idea is that you would drag and drop files from one screen to the other, and this would make the files transfer from one computer to the other. But all I got was a dialog box telling me that it could not find a remote computer. (This box appeared on both computers, by the way.) After a few hours of fiddling on this, I decided to read the manual, and on the very last page in the troubleshooting section it says "do Not use your printer cables, you have to use our special Laplink cables". Which of course they did not supply with the laptop. But which they would be happy to sell you for 70 bucks.
So, I wandered back to my switchbox / cable store, and asked them if they stocked Laplink cables, and they said sure, have one right here, Nine dollars cash! And that fixed the problem.
So now, my two computers can communicate with each other (by using the proper cable), or they can both (separately) talk to the color printer, all this without network adaptors, hubs, or software.
Having gone through all this effort, and written the article, I now believe that probably an in home network is the correct solution. Now, a year later, the hardware to network two home computers runs about $150. While that is more than what I paid for this setup, it is far more flexible. If I ever do this over, that is the way I would go.