Tandy Disk-Video Interface. (evaluation) David H. Ahl.

Although the Model 100 is great for travelling, the lack of a reasonable size display and limited storage capacity are severe drawbacks to using it as your main computer in the office or home. Now, Tandy has a solution. The Tandy Disk/Video Interface gives you both 40-and 80-column composite video output (for a monitor or TV set) and a single 5-1/4" disk drive (with room for an optional second drive). The disk with the Interface includes the operating system and Disk Basic. Approximately 170K is available for storage of user programs.

The Disk/Video Interface connects to the Model 100 by means of a 20" ribbon cable that terminates (at the Model 100 end) in a 40-pin DIP connector. As owners of Apple joysticks know from bitter experience, a DIP (dual inline package) connector has 40 easily-bent pins. (Our Interface arrived from the previous reviewer with 26 of the 40 pins mangled.) To minimize problems with the pins, Tandy includes a quick release adapter socket that plugs permanently into the female connector on the bottom of the Model 100. Nevertheless, we would have preferred an adapter that terminated in something other than a DIP connector, but perhaps size dictated the choice of connector.

Incidentally, if you have any ROM software installed in the bottom socket on the Model 100 (say Disk + from Portable Computer Support Group), it will not interfere with the use of the Disk/Video Interface as it uses a different socket.

This Disk/Video Interface comes with a 64-page manual consisting of four sections. The first provides general information on installation and use of the system. Part 2 describes all the new disk Basic commands. The third section describes the file structure and format of the floppy disks, while the last section is a set of appendices detailing the technical aspects of the system, error codes, and ASCII character tables. Firing Up

Once you have connected everything up and turned on the system, a message appears on the CRT indicating a correct startup. Interestingly, you still use the menu on the Model 100 to select what you wish to do.

Parameters such as screen width (40 or 80 columns) and function key labels on or off (on bottom line of screen) must be set from Basic. From then on, everything that you do from any program--Basic, Text, Telcom, Schedule, and Address--appears on the video display except, as mentioned, the main menu.

The operations of all the programs is exactly the same as with the LCD screen, except you see three to six times as much on the display. Files are saved in the normal way, except that to save to the disk, you must precede your file name with a 0: indicating disk drive 0.

The manual makes much ado about disk Basic, and indeed there are several additional commands for file access and the display, but it is hardly the much extended Basic that the manual implies. Additional file commands include OPEN, CLOSE, PRINT # (write to disk), INPUT # (read from disk), LINE INPUT # (read line of data), DSKO$, DSKI$ (write and read string in specified sector), LOC, LOF, and EOF.

Two video functions were added: CSRLIN (returns vertical coordinate of cursor) and POS (returns position of cursor). In addition, CHR$(27) can send to the video screen any of 20 control codes, including cursor up, cusor home, erase to end of line, insert line, clear display, reverse video, and move cursor to a specified location.

the disk with the system also includes two utility programs, FORMAT and BACKUP.

Compared to a state-of-the-art desktop computer, the disk drive is relatively slow, which is not surprising given that it doesn't use a true operating system. On the other hand, it doesn't seems slow at all because you are usually moving comparatively small amounts of data back and forth. Worth The Price?

The Disk/Video Interface is easy to install (despite our quibble with the DIP connector) and easy to use. It works well, and the documentation is very good.

However, the unit is priced at $799, and Tandy seems to be holding the price line. This seems quite expensive considering that you can buy an entire computer, disk drive, and monitor for about the same amount. However, that is probably not a fair comparison, and therein lies the rub: there is no directly comparable product.

If your main application is text editing, an alternative to the Disk/Video Interface is a disk load program like ones available from Kensington Microware and Portable Computer Support Group (PCSG). For example, Disk + from PCSG lets you save and load files back and forth between the Model 100 and a desktop computer through the RS-232 port. Those files can then be edited with a word processing package on the desktop machine. Complete with cable, it costs about $120. Many desktop computers, including the IBM PC (and clones), Epson QXz-10, and TRS-80 Model III and 4, are supported.

However, if your goal is to have your Model 100 serve as your primary computer both on the road and at home base or if the extended file capabilities of Basic are important, the Desk/Video Interface is a capable and worthwhile product.

Products: Tandy Disk-Video Interface (computer apparatus)