The Tandy Model 100 gets a boost from this quick and easy to use interface, says Geof Wheelwright

Since the introduction of the lap portable, its main drawbacks have been lack of memory and the size of the screen display. Tandy, however, has come up with a solution that is available now for its Model 100. It's a disk/video interface that gives you both 40- and 80-column composite video/TV output as well as one 5.25" disk drive and room for an optional second drive.

The interface is a big white box that comes packed in the obligatory styrofoam and cardboard casing. When you get the casing off, you'll find a manual, a disk with the Model 100 'Operating System' on it and the disk/video unit itself.

Before you get going, you'll need to do two things; first, put an electrical plug on the disk/video interface, and second, make sure your Model 100 has the 'B' ROM chip fitted. This ROM is important in that it contains the necessary disk and video interface commands.

Tandy isn't charging anything for the 'B' ROM chips to upgrade existing Model 100s, but it requires the upgrade to be carried out by a dealer service representative - who must charge you a fiver for his time.

Anyway, once you've spent your fiver and put on the plug you're ready to hook up the interface. It attaches via a 40-pin lead that's about as sturdy as an old Apple II joystick connector.

The Apple II joystick connector was famous - or infamous - for its constant pin-bending activities, which inevitably resulted in yet another trip to the service department or the purchase of yet another lead. Given that you would probably want to be able to hook and unhook your disk/video interface quite freely, it doesn't make much sense to use a fragile 40-pin connector as the linking point.

It wouldn't have been hard to have a wedge-shaped adaptor (like the one on Sinclair Spectrum Interface 1) that hooked on the back of the Model 100, giving it some much-needed height and a good typing tilt as well as providing a sturdy amphenol plug that could be plugged and unplugged without any problem.

The interface comes with a single manual which is nice and chatty, in true Tandy/American style.

The manual consists of four sections. The first tells you how to set the system up and provides a number of pretty pictures. Part two describes all of the new commands available to run the disk system. The third section comprises an in-depth analysis of the disk format, showing exactly how it is laid out.

The final section is basically a set of appendices detailing the technical aspects and containing tables of ASCII and error codes. Overall, the manual covers virtually everything you might need to know about the system.

If, by any chance, you need to know more, Tandy also have a service manual available. This covers every technical detail you could possibly want - from taking the disk drive to pieces to the electronic circuitry and the signals it produces.

The design of the disk/video interface is consistent with the Model 100: simple to use and limited in its power.

Once you've connected things up, just stick the Operating System diskette in the top drive (there is only one drive on the basic interface, but an optional second drive - which fits below the first in the same box - is available) and switch on both your monitor and the interface.

Then you turn on the Model 100 and you're ready to go. The disk is immediately available to you for storage, but you have to give a command from Basic to use the monitor. The commands SCREEN 1,0 or SCREEN 1,1 (depending on whether or not you want the bottom line of the screen taken up by prompts) will transfer all subsequent information to the screen and will cause the monitor - rather than the LCD - to be the boot-up display from that point onwards.

It's worth pointing out that although everything in Basic, Text, Telecom, Schedule and Address appears on the monitor, the main 'menu' at power-up still appears in the LCD, turning it into a sort of microscreen from which programs and files are selected.

As you're not likely to be switching quickly between files too often, having the main menu on the LCD is not a great drawback.

Changing from the 40- to 80-column display is also pretty easy. It's a statement from Basic in the form: WIDTH 80 for 80 columns or WIDTH 40 for 40 columns. The 80-column display does add a good deal to the powerful word processor built into the Model 100. Text, the simple name given to the word processor on the Model 100, NEC PC-8201 and Olivetti M10, has the capacity for string-searching, variable width printing, block moves and deletes, automatic word wrap and full screen editing.

The disk drive is relatively quick - but so it should be, given the comparatively small amounts of data being shoved back and forth between the disk and the Model 100's limited 32K memory. The single-sided, double-density drive offers about 170K of formatted storage.

Aside from my quibble with the connector my only other reservation about the device is the price. At £599 including VAT the interface is a little on the pricey side. But then, Tandy has never been about low prices; instead making things easy to use and offering excellent service, back-up and dealer support for its products at a competitive price.

The great thing about the interface is that it's quick to hook up and very easy to use. So it's a trade-off between convenience and price. A less convenient way of doing the same thing at a lower price would be to get a BBC Micro with disk drive and write routines that send information to and from the Model 100 through the RS-232 port in order to make use of the Beeb's disk drive and scren.

LFILES
Displays the filenames on the disk

SCREEN
Assigns the console to a specified device

WIDTH
Sets the screen width

DISKO$
Writes a string to the specified sector

DISKI$
Gets a string from the specified sector

LOC
Gets the current record number

When the new Kyocera breed of LAPPIES (Largely Available Portable Processing In Every Sense) computers were first released in their respective Tandy Model 100, NEC PC-8201 and Olivetti M10 configurations, I was charmed by their size, power and ease of use.

I also hoped that these portables would grow up and be able - when necessary - to take more memory, use disks and run a cathode ray tube screen display.

The NEC machine pretty much solved the memory question with its bank-switching system that allowed up to three banks of 32K to be accessed in turn. One of those memory banks comes in the form of an optional 32K memory cartridge which can be plugged in the left-hand side of the machine.

A 32K memory cartridge, however, is not a disk - it doesn't act much like one (and at more than £150 a time, it certainly doesn't cost much like one) - and the Kyocera LCD screens are still only 40 columns wide by 8 lines.

NEC was rumoured to have a solution that involved a plug-in disk interface/ROM/80-column video outlet that not only gives you access to a full 80-column display from your portable, but also the use of a 5.25" disk drive and the CP/M business operating system on a chip. That solution still have not appeared in this country.

Tandy, however, has come up with the goods, although the system still lacks a standard Operating System. It is possible that some enterprising entrepreneur will come up with a CP/M system that will work with the Model 100 making a lot more software available.