Classic Computer Magazine Archive COMPUTE! ISSUE 42 / NOVEMBER 1983 / PAGE 40

Adding Peripherals

Building A Home Computer System

Ottis Cowper, Technical Editor

Taken together, peripherals can end up costing more than your computer, so making the right purchases is a must. What brand should you buy? What "extras" are needed? Will you need software just to operate your peripheral? This article helps define the more critical issues involved.

Computer enthusiasts often brag about their "systems," adding an aura of sophistication to their home setups. These systems usually consist of a basic microcomputer surrounded by an assortment of peripherals. Essentially, a peripheral is anything you plug into your computer.

Without even realizing it, you started adding peripherals and building your system as soon as you bought your computer. Your first peripheral was most likely a TV or video monitor, and the next was probably a cassette tape unit to load and store programs or a joystick to use with your favorite game. From there, the list of possible peripheral devices goes on and on: printers, disk drives, modems, memory expansion cartridges, light pens, speech synthesizers, plotters, etc.

It's up to you to decide which peripherals you need: a disk drive for serious word processing, a color monitor for really sharp video displays, a modem for telecommunications. The economics of the situation should dictate the amount of time you spend comparing the available models of the item you want.

If you have been shopping for any of these items, one thing you've realized, is that it's not at all unusual for a peripheral device to cost quite a bit more than the computer to which it is attached. It might take you a while to get adjusted to the idea of hooking a $600 printer up to your $100 computer. But the overriding issue is compatibility: Will the peripheral you want work with your computer system? It's easy to see that you should choose your peripherals carefully.

Which Brand Is Best?

The obvious way to guarantee that the peripheral devices you buy will work in your system is to buy them from the same company that made your computer. Another source is the alternate "third party" suppliers and many of them offer truly innovative designs.

Most home computer peripherals are someone else's product wearing a new name. The computer company buys the hardware in huge quantities from the original manufacturer and then puts on its own brand label. In many cases, a similar product is also available directly from the original maker.

The key to whether a product is a better buy from the original manufacturer or the reseller can lie in whether the reseller just slapped on a logo or whether the product was modified to optimize its performance in conjunction with a particular computer. This isn't usually something that is obvious. One way to check is to see if the peripheral supports any of the computer's special features. For example, Commodore computers have a set of built-in graphics characters which are directly accessible from the keyboard. Commodore sells a printer made by another company, but modified to print the special characters. Similar printers are available under other brand names, but the others either will not print the graphics characters or will print them only if you pay extra for an additional ROM chip and install the chip in your printer.

Read The Fine Print

Price should not be your sole concern when deciding what peripheral to buy. An important factor to consider is ease of interfacing. Again using printers as an example, a $300 printer that requires a $75 interface module to be used with your system is not a better buy than a $350 model that would plug in directly. Moreover, all interfaces are not created equal.

We recently saw an interface which could be used to connect the VIC-20 to a popular brand of dot matrix printer. We assumed at first that using the interface was simply a matter of plugging one cable from the interface into the computer and another cable into the printer. It was only when we read the fine print in the instruction manual that we discovered we had to go inside the printer and solder in a wire to provide power for the interface. Such a modification would certainly void any warranty on the printer, and should not be undertaken thoughtlessly. This is the kind of detail that you need to investigate thoroughly before you buy any peripheral that doesn't plug directly into your system.

You should also check to see if any special cables are required to connect the peripheral to your computer or to the necessary interface. Many buyers have been dismayed to arrive home with a new peripheral only to discover that a special cable is required to hook it up to their system. They can get even more dismayed when they discover that the manufacturer wants $35 for the necessary cable. Owners with some soldering experience may be able to save some money by building the cable themselves if they can find the necessary connectors, but, again, it's really not a job for beginners so you should make sure that all necessary cables are included with the peripheral.

The Software Issue

Yet another item to consider is support software. Some peripherals require no special software; others are useless without it. For example, the same light pen can be used interchangeably on an Atari, VIC, or 64. However, without software to read the light pen and convert the value for the light pen position to an equivalent screen location for your particular machine, the pen doesn't do you much good.

If you're not a sufficiently advanced programmer to write your own support software, you should be sure that programs for your computer model are included with the hardware. This is especially true for complex peripherals like speech synthesizers and plotters. If you don't get software for your computer with the device, you can face possibly spending quite a bit of time developing your own.

Lack Of Standardization

There are few standards for home computer peripherals. Much of the lack of standardization is the result of the various companies following different design philosophies. For example, the mechanical workings of all 5-¼ inch floppy disk drives are essentially identical, but drive units for particular computers are not at all interchangeable. Using the same basic hardware, a Commodore drive stores data on the diskette in 683 256-byte sectors; a TRS-80 Color Computer drive creates 630 256-byte sectors; an Apple II drive, 560 256-byte sectors; and a Texas Instruments drive, 360 256-byte sectors. An Atari drive uses 720 sectors, but each sector is only 128 bytes long. The Commodore writes the directory on track 18 of the disk, the Apple and TRS-80 on track 17, and the TI on track 0. This not only makes the disk drives incompatible, but also means that disks written by one brand cannot be read by another. Each manufacturer has strong arguments why the particular method it chose is the best, and no one seems willing to compromise in the name of compatibility.


A few attempts at standardization have been made. For example, a company called Centronics was one of the first major suppliers of computer printers. Centronics used a parallel interface scheme in which data was sent to the printer one byte at a time. Companies which entered the market later used Centronics' connection so that their printers could be easily attached to computers set up for Centronics printers. So this connection scheme, with its 36-pin plug, became the de facto standard, and Centronics parallel interfaces are now available for most home computers.

A more formal standard has been established for serial data communications. The standard, called RS-232, calls for a set of wires including a transmitted data line, a received data line, and a collection of "handshaking" signal lines to regulate data transfer. Moreover, a particular type of plug called a DB25 is almost always used on RS-232 data lines, and each pin on this plug has been assigned a particular RS-232 signal. So if you have an RS-232 port on your computer, you can interface without problems to an RS-232 peripheral, right?

Unfortunately, it's not always that simple. The RS-232 standard defines a set of signal lines, but fails to specify what shall be considered a valid signal on those lines. Some RS-232 systems use +12 volts and -12 volts as the two signal levels, some use +5 volts and -5 volts, and a few others use +5 and 0 volts. For example, the VIC-20 and Commodore 64 have the ROM software built in to support RS-232 communications through the user port on the computer, but you still must plug an interface module into the user port to increase the output voltage levels before you can use most non-Commodore RS-232 devices. You should be aware of this before purchasing any RS-232 "standard" equipment.

At some point in the future, one company may come to so dominate a sufficiently large share of the home computer market that it determines the standard for everyone. Some are predicting that IBM's new home computer, due to be released soon, will become the archetype. The Japanese are reportedly attempting to develop a set of standards to reduce incompatibility problems in their new generation of home computers in the hope that they will come to be the standard. For now, the name of the game is caveat emptor, let the buyer beware. For any given computer there is much more incompatible than compatible equipment available.