The title of this article represents a small amount of literary license in that I have borrowed on the recollections and knowledge of other people in its preparation, with special credit due to Art McAninch, Jr.. Art is a great repository of Model I hardware, software and lore, and is really the man to talk to about the Model I.
The Model I was Radio Shack's first venture into computer manufacturing. It was not their first offering in the market place. Indeed, I have an old catalog of theirs which predates the RSC-x series of catalogs, and it lists some S-100 stuff! But the Model I (it did not originally have a model number, it was just the TRS-80 Computer) was my first desk top machine, and like other first loves, it sticks in my memory.
I bought mine with the LARGE memory, 16K, if you please, as opposed to the standard 4K which normally came with the Level I! I believe that cost me an extra $100 when I bought it. It was the Level 1 version because that's what the store had on hand and I was anxious to get it home and play with it. I upgraded to Level 2 at a later date (for another $100).
What is the difference between the Level 1 and Level 2 ROM's? The Level 1 ROM was a 4K ROM which contained the cassette operating system (OS) and a version of BASIC known in that era as Palo Alto Tiny BASIC, written by a gentleman named Wang, I understand. The Palo Alto BASIC was very limited in size, and could only accommodate TWO strings, A$ and B$. It also was very limited in variables, 26 being allowed, and those were the letters A-Z, of course. The OS was cassette only, and was not a DOS. That came later. Tiny BASIC was delightful in one respect; most commands could be abbreviated to a single letter. You sure could write tight code with it!
Level I was a marvel of simplicity and terseness. It only had two diagnostics, which were WHAT? and SORRY. WHAT? meant you had a syntax error, and SORRY was sort of a catchall, which could mean almost anything.
The Level 2 ROM was a 12K set of 1, 2, or 3 chips (there were several versions of the Level 2 chip set) which was still a cassette OS, (by Microsoft) but which had built in "hooks" for a future DOS to connect to. Level 2 allowed far more variable names for both numeric and string variables, and you could do a lot more with it. Unfortunately, you now had to spell out all the commands; ? for PRINT was the only remaining single letter command abbreviation. Also, L? would not work in place of LPRINT; (I tried). But you could still pack BASIC statements with no spaces between symbols. That was the era when we learned how to pack BASIC so tightly it became unreadable! A write-only language, you might say! I remember several people wrote some clever utilities which would unpack and print out any BASIC listing in elegant and readable form, even a program which could not otherwise be easily analyzed.
For a while, a trick was popular which involved having both Level 1 and 2 available in the same machine, selected by a toggle switch. The idea was clever, but it was difficult to implement because of the varied physical configuration of the level 2 ROMs and because of the additional power required. The switch selected an enable line of one or the other ROM(s), giving either Level 1 or 2 operation. Shifting on the fly was not permissible; the machine would bomb. A reboot was necessary in order to achieve operation in the other BASIC.
The power supply for a Model I was a small black cube, about 3" on an edge which plugged into the power strip and had a trailing cord which plugged into the keyboard or EI. The cube was factory sealed with solvent, and could only be opened with a sharp knife or a hacksaw. When a power supply died, the knowledgeable owners knew to open it up by whatever means to gain access to the small fuse soldered inside! Never before have I seen a fuse hidden inside a piece of equipment such that it was not reasonably replaceable. Two of my power supplies are presently taped together because of this "undocumented feature".
As originally designed, the Model I keyboard had +5 Volts available on one pin of its 40 line bus. I never knew why it was there, but in theory you could use this 5 volts to power some outboard accessory. However, RS soon decided this feature was a liability, as you could easily overload the power supply serving the keyboard. Thereafter, whenever your Model I keyboard went into a RS Computer Center for modification, repair, upgrade or whatever, the technician always cut the 5 volt source to this pin, and grounded the pin instead.
The Model I also had only upper case symbols in its screen display, as RS did not anticipate anyone doing word processing on it. In order to save about 10 cents per machine, they omitted the static memory chip for bit 6 of the screen memory, and did a little peculiar logical arithmetic which finally sent an address into the character generator ROM and caused it to output an upper case character whether you typed upper or lower case into it. This bit of logic was the cause of some strange errors in BASIC. For example, if you accidentally input a lower case version of some letters, the resulting internal representation was not per the rules of BASIC and would cause SYNTAX ERROR to appear; yet the line looked OK! As I remember, the "@" sign was one of the trouble makers.
Several solutions were developed for the problem of the missing lower case. Remember, the character generator contained the lower case character set, it just couldn't be accessed by the original firmware. The most popular fix was to add a 1 bit X 1024 static memory chip (a 2102) piggy backed on top of one of the seven original static memory chips. One trace cut and two jumpers were required to complete this fix. This fix became known generically as the "Electric Pencil" fix, because Electric Pencil users needed the lower case capability, and they showed in their manual how the customer could do it.
Unfortunately this fix gave rise to the notorious "flying a". For some reason, the character generator ROMs used by Radio Shack had the lower case "a" stored in such a way that the "a" was one or two scan lines too high on the screen. This did not affect the printed output, of course, but it sure looked funny on the screen until you got used to it! One of the apochryphal stories about this "feature" was that supposedly some other customer ordered a large batch of character generator ROM's and the ROM manufacturer located the "a" incorrectly. Radio Shack then was alleged to have bought the batch of defective ROM's "real cheap" and worked out the upper case only routine so the ROM's were usable. Who knows the truth?
However, simply adding a static memory chip revealed what else Radio shack had been doing to the firmware. With the additional memory chip installed, the firmware now called for control characters from the character generator and the machine now produced gibberish at boot time, and required a software routine to produce valid letters.
This lower case fix of adding a static RAM chip became the de facto standard, and the designers of after-market operating systems all included some logic to detect whether the machine had the extra RAM chip or not, and would handle screen displays correctly. Except Radio Shack, who had to do the fix differently! They did something else to the circuitry, I don't remember what, which made their software a little different than the aftermarket software. The aftermarket people then had to incorporate another wrinkle to detect the Radio Shack fix and apply the necessary logic to it.
Yet another lower case fix was offered by The Electronic Closet, 8187 N.E. Blakely Court W., Bainbridge Island, Washington, 98110; they are still in business and offer a substitute ROM to go with the added static memory chip. Their character generator has an extra set of lower case letters in it, one where ASCII code expects it, and another which replaces the control characters! With this setup, you can have lower case in cassette operation and all disk software works properly also. The only problem is you can't have control characters on the screen even if you try. There aren't any! They also offer other features, including custom ROM's and a selectable alternate character set, such as Greek or French or whatever.
Another problem with the Model I was the lack of a CONTROL key. Electric Pencil by Michael Schrayer (which was ported over from the CP/M world) needed a CONTROL key. The same page in the manual which showed how to add the memory chip for lower case also showed how to add the missing control key. The keyboard matrix allowed for the key, it simply wasn't there. The fix was to install any available momentary contact push switch somewhere on the keyboard and attach it electrically to the empty position in the matrix. You should have seen the modifications which sprouted on the Model I's owned by the more adventurous! This particular fix was obviated when Michael Schrayer rewrote Electric pencil to use the CLEAR key as a CONTROL key. This also became a de facto standard. Any programmer who needed a CONTROL key and who did not need the CLEAR key simply programmed the CLEAR key to be interpreted as the missing CONTROL key.
The Model I was notorious for bouncing key contacts. The actual keys on the keyboard actuate tiny switch contacts underneath the keycaps. If the tiny contacts bounce excessively, the keyboard scanner software may interpret this as multiple presses of the key and put multiple images on the screen. Some keyboards were far worse than other. Three different fixes were available. One was to attempt cleaning and adjustment of the contacts. In the original keyboard, the keycap could be pulled straight up and off, exposing the contacts to the tender ministrations of the owner or his friend. Sometimes cleaning and/or bending of the contacts improved matters, sometimes things got worse. Very iffy. The second fix was to modify the scanner software so that it would wait longer to decide if the key was closed or not. RS offered a software fix for the Level I Model I in the form of the KBFIX tape cassette program. This loaded in and replaced the scanner in ROM and did help the situation. I don't remember what they did for Level II. Disk systems included the improved scanner as part of the DOS. The real fix came later as a new keyboard, made by ALPS and known to us by that name. The keys were shaped differently, which allowed easy external identification, and the keycaps were no longer removable. The ALPS keyswitch was quite different internally and was a vast improvement over the original. The Model III and later machines got the ALPS keyboards from the beginning.
Unreliable cassette operation was a problem with the original version of the Model I. The machine appeared to be critically sensitive to the playback level of the cassette when loading files.
One of the aftermarket devices offered was the Data Dubber, about a $50 item which was supposed to clean up the waveforms and allow easier loading of cassette files. I know they sold a lot of these, but I don't know how successful they were in improving loading. I am sure they were on the wrong design track in tackling the problem, as the real problem was a timing problem in the ROM.
After a year or two of complaints, RS announced the solution to the problem and a fix. The problem was a bad assumption made when the ROM was designed. The fix compensated for (but did not cure) the bad design and was designated the XRX board. It was a small board, about 2" x 2" with a couple of chips on it, a few wires to be soldered to the keyboard, and a couple of trace cuts. I had it added to my machine, and the improvement was magical. From a delicate adjustment of the volume control, operation went to almost no concern at all about the volume setting. I just left it at midscale thereafter and never had to touch it again. Radio shack would install this fix for free if you complained loudly enough. This was fixed in software in some of the later Model I ROM's, those that showed "MEM SIZE" on the screen at boot up, as opposed to "MEMORY SIZE".
Originally RS supplied a CTR-41 cassette recorder with the Model I. Later they changed to a CTR-80 machine. And then the troubles began! Owners besieged RS with complaints that the recorder was damaging prerecorded tapes. RS refused to believe this was possible. Finally the truth came out. If the recorder's STOP button was actuated in the middle of a playback sequence, the signals on the tape would be garbled. But how was this possible? When the STOP button was actuated, the motor current was interrupted, and an inductive kick was generated which somehow fed back to the record/playback head which put a glitch on the tape. But why didn't the CTR-41 do the same thing? And what could be done to cure the problem? I don't know all the answers here, but evidently the internal circuitry of the CTR-41 was sufficiently different that the inductive kick of the motor did not reach the record head. As for the cure, I don't know what that was, either, but anyone who had the problem could take his CTR-80 to RS, who would wave their magic wand over the internals and make the CTR-80 stop messing up the tapes.
The pink pearl treatment was another trick discovered to keep the Model I working adequately well. The original problem was penny pinching by Radio Shack. The edge card connectors of the keyboard and the expansion interface (EI) were originally tinned with lead/tin alloy solder instead of the more professional gold plating. This worked fine initially, but eventually and gradually the lead would oxidize, which caused the edge connector to become plated with lead oxide instead of solder. The lead oxide was a semiconductor, and would interact with the 5 volt signals to cause strange values to appear on the buses, with disastrous results. Usually, the machine would simply cease operating (freezeup or lockup), necessitating a RESET to regain control. Spontaneous reboots were also commonplace. Someone discovered the Pink Pearl pencil eraser would clean the coating of lead oxide off the edge connectors, and everything would work OK again for a month or two. This became a ritual with Model I owners. Then along came EAP Co of Keller Texas. This outfit discovered a source of male edge connectors which could be soldered over the deficient solder tinned edge connectors, and which in turn had gold plated fingers. With these connectors installed, the spontaneous reboots and freezeups went away. EAP is still in business today, if you need the connectors.
Art McAninch reminded me of some other ingenious uses of the pink pearl erasers. Since the density doubler board plugs into the bottom of the expansion interface, there is a tendency for the doubler to work loose and fall out of its socket. A suitably carved pink pearl makes a useful spacer to hold the doubler in place. The RS-232 board had a different problem, and some people found a pink pearl was helpful there, also.
Those who bought a Model I without an expansion interface (EI) had several limitations to contend with. One was limited memory. The keyboard had either 4K or 16K (Max) of RAM. The other 32K was only available if you added the EI. Secondly, the floppy controller and the RS-232-C interfaces were in the EI, so you were limited to cassette operation only, and no Serial port if you lacked the EI. And finally, NO PRINTER. The printer interface was also in the EI. Of course when the cost of printers was $1000 and up, (the keyboard-only machine went for about that amount, also), most of us couldn't afford new printers. Therefore the lack of a printer port was just another minor complaint. But to their credit, RS did come out with a printer interface that plugged into the keyboard, so as printers came down in cost, the port (for about $100) could be made available. Of course the port consisted of only about 6 chips....
The original RS expansion interface was a problem. As long as you operated it only as a cassette system, it usually worked adequately. But when floppy disks came along, it shortcomings became evident. Apparently the root cause of trouble was bad signal timing on the bus brought about by poor design of the bus. RS originally blamed the trouble on "non-Radio Shack" memory chips installed by owners unwilling to pay their exorbitant price for chip sets.
When this explanation failed to explain all the observed troubles, they dug deeper. The next fix was a small additional cable between the keyboard and the expansion interface spliced by means of a small DIN connector. This too was only a patch, and the troubles continued.
The next fix was the addition of a special 40 line cable between the keyboard and the expansion interface, known as the "pregnant cable" because of the small black plastic enclosure in the middle of the cable which contained a couple of buffer chips. This fix had an unintended side effect. Since the pregnant cable required +5 volts, RS elected to change the function of a ground line between the pregnancy and the expansion interface. One of the ground wires was reassigned for use as a +5 volt wire. If, later on, an unmodified cable without the pregnancy was connected to such a modified expansion interface, it promptly blew the inaccessible fuse in the power supply serving the expansion interface!
The final fix to the bad expansion interface problem was a new expansion interface board design which got rid of the bad design features and which could be relied upon to work properly. Radio Shack did this, and even kept it physically compatible with the old board so it would fit in place of the previous bad board in the same case, thus avoiding the need for a new case.
Radio Shack strongly believed the customer should stay out of the internals of his computer, and so the Model I keyboard and the EI each had one of the enclosure screws covered up with a bit of sealing wax, or something similar. If you wanted warranty service and the wax was gone, you were out of luck. When they worked on it for you, they put a special sealing label over the screw head. I can remember waiting for my warranty to expire before I dared to cautiously open up my keyboard. That was in the beginning. Later, I seldom bothered to put the screws back in place; I just slapped the boards into the case and dropped the top cover on it, and that was that.
An interesting sidelight to this problem of the deficient EI was the creation of a new company known as LNW Inc. which was in the Orange County area of southern California. This company took note of the RS design problem, and resolved to design a new EI board of their own which would function properly. They succeeded and were a factor in the Model I arena for a couple of years. They built up several different Model I-like machines, the last of which was called the "Team" machine. I never knew where the name Team came from. Their machine had provision for color, alternate CPU's, and some other features. Unfortunately, they lacked sufficient capitalization, and they were effectively following RS, not leading. They finally folded.
Another quirk of the Model I was the floppy drives. The original drives were 35 track, single sided Shugart SA-400's at a shocking price. The floppy drive industry was just taking off at that time, and apparently originally thought 3 drives was aplenty for a machine. Radio Shack, to their credit, figured they should design for 4 drives.
Needing a 4th drive select line, they opted for unused line 32 in the ribbon cable. To simplify inventory stocking and to keep customer's icky fingers out of the drives, RS developed the "pulled teeth" concept for the ribbon cable which connected as a daisy chain to all 4 drives. The effect of this was that all four drives were addressed with all drive selects enabled. The 4 connectors on the cable were unique, each one having only one select finger intact, the other three being missing. Thus the position on the cable determined what the drive number would be, and the internal drive select jumpers were never altered.
Note that the concept of a universal drive which did not have to be internally addressed by the installer was such a good idea that IBM adopted it, with a variation, for their PC machines. In their scheme, all floppy drives are also addressed the same, and the curiously twisted floppy cable takes care of the actual addressing.
However, when Shugart (or someone else in the industry) decided a 4th drive select line was necessary, they decided the 4th select line should be line 6. Worse, double sided operation was being developed, and a side select line was needed. Another someone in the industry decided the logical one to use was line 32. But Radio Shack had already assigned line 32 as the 4th drive select line! Alas and Alack! What to do about the problem of four double sided drives?
Radio Shack came up with a solution. Ignore the problem and hope it will go away! It didn't. The outside DOS vendors decided the only way was to allow four SS drives, or three DS drives, and this required a new ribbon cable with all teeth intact, no pulled pins. So junk your old ribbon cable and go buy a new one with 5 connectors on it with all teeth intact. $Ouch!$.
And then along came an unsung genius/hero who noted two things. First, the ribbon connectors were reversible; that is, they would plug onto the edge card connectors either way if the little key was removed (it was often missing, anyway). Second, all the odd numbered connectors were ground, and only the even numbered connectors had functions assigned. The genius part was to recognize that if ALL five connectors on the drive cable were turned 180 degrees, then the previous even lines (with some teeth missing) all became odd numbered ground connectors, and the previous odd lines (with all teeth present) became even numbered signal lines. Suddenly the missing teeth problem was moot, as no more than three were missing on any one connector and the remaining lines were ample for grounding purposes.
The remaining part of the solution was to revise the addressing on each drive so the drive would respond to only one address line, instead of all four, and the side select function would respond to address line 32. Now DS operation with 3 drives was feasible for the Model I.
The floppy disk controller (FDC) originally chosen by RS was not able to separate data pulses which were very close together. With 35 tracks, the system worked adequately; with 40 track drives, the high numbered tracks were sometimes unusable. PERCOM solved this by offering a data separator designed to work with the FDC and reliably sort the data out of the noise.
Double Density was a whole new ball of snakes. The original floppy disk controller was the WD-1771, designed only for single density (SD) operation. Since the Level II ROMs in the machine knew almost nothing about reading disks, and what they did know was limited to single density, the boot track (zero) had to be in single density, no options. Several designers of double density adapters considered the problem long and carefully. Their solution was to have TWO floppy disk controllers (FDC) in the machine, the original WD-1771 working in single density to boot the machine, and a second FDC able to operate in double density. A data separator was included to make the operation reliable. The DOSes then had the smarts to know when to enable one or the other of the two FDC's. But wouldn't you know, after PERCOM had established a workable technique which was acceptable to the aftermarket DOS authors, then RS had to do it differently (probably in a futile attempt to control this niche of the market) which muddied the water for everyone. The result was the aftermarket DOSes had to be revised to tell the two schemes apart and work properly with either one. Radio Shack wrote some new software to work only with their own scheme, but the whole issue soon became moot, due to the arrival of the Model III on the scene.
Did you know the RESET button on the Model I (and a heck of a lot of other machines, including CTL-ALT-DEL on the IBM) is not a RESET at all? On the Model I, the RESET button was actually wired to the NONMASKABLE INTERRUPT of the Z-80. Now you know why some lockups could not be overcome by hitting the RESET button; it never was a RESET! What was supposed to happen was the Z-80 would jump to a location (66D, I believe), and execute the recovery code chain which began there. But most of the code chain was in RAM, loaded there at BOOT time, and if the software bomb which locked up the machine altered any of this code, then you could not recover control with the RESET button. When such an unrecoverable lockup occurs, the only solution if you don't have a real RESET button is to turn the power off, wait awhile, and turn it on again, which of course loses everything you had in memory. To overcome this little trick, I wired an extra push button to the actual RESET line of my Z-80, and as long as I did not hold it down more than momentarily, I got an honest RESET which would overcome ANY software problem. Some knowledgeable IBM types do this today to their machines, for the same reasons. The RESET terminals exist on the IBM motherboard, they just don't connect to anything.
The Model I had an optional RS-232-C board which mounted in the top structure of the Expansion Interface. It suffered greatly from erratic contact between pressure contacts on the board and in the well of the EI which housed it. Due to poor design, the contacts often failed to make good contact, and the RS-232 would become erratic. Several tricks were developed by users to solve this problem, including use of the pink pearl as a spacer cum spring, mentioned earlier. None of the tricks were really neat, in my opinion. The best was to eliminate the spring contact system and solder a piece of cable in place of them, which yielded a solid, reliable system.
By this time, Radio Shack realized they had a good thing going in the Model I, but it had glaring deficiencies. The most stringent was its inability to meet a newly imposed set of FCC radio frequency interference (RFI) limitations. In fact, the Model I is notorious for the RFI crap it puts out. The FCC rules going into effect were so tough that the existing Model I could not meet them without major repackaging, and all of the foregoing narrative shows its other weaknesses. The solution was to redesign and repackage the Model I into the Model III, keeping the same logical layout for upward compatibility of software, fix all the worst features, including lack of lower case, lack of double density, lack of a decent RS-232, excess RFI, add built-in power supplies, more reliable and higher speed cassette operation, make provision for a hard drive, but still no double sided operation. The Model III is quite a good machine. And it was a one piece machine with almost no external cables for people to complain about.
Hard drive operation on a Model I was provided for, but only as an afterthought. Initially, the hard drive package was only made available for the Model III. Later, an adapter kit (No 26-1132) was offered which would permit operation of the 5 Meg hard drive package on the Model I. The package included LDOS 5.1.3 from MISOSYS, the adapter, and the TRSHD driver software.
One of the Model I's quirks was its behavior when a print operation was called for with no printer connected, or if the printer was connected and was non-functional. If you hit LPRINT or LLIST without a working printer, the Model I would wait forever before doing anything else. You had to reboot it to recover, which usually meant losing something you were working with. I once built a little connector which went on the printer edge card connector instead of the printer. This connector had a couple of pieces of wire on it so it acted as if a printer in the ready mode was always connected. I simply grounded the Paper out and BUSY signal, as I remember. This made the non-existent printer seem to be always READY, and never out of paper. The computer would then send all its data to the port, and quickly come back to Ready. I thought this was a nice little device.
As you know, the original Model I video display was a factory modified RCA television receiver, and it came with the short persistence, blue-white TV tube in it. Tough on the eyes. A company named Langly-St. Clair offered amber and green replacement tubes which you installed yourself. The amber tube had longer persistence than the the original TV tube. The green tube was even longer. In fact, the green was so slow that some people complained about the effect it had on the animation of some of the graphics games!
The Model I had a built-in relay on the keyboard to turn the tape cassette motor on and off. Unfortunately, the relay contacts tended to weld together, probably because the motor current was higher than the relay could safely handle. The result was the motor would continue running even when the software told it to stop. The temporary cure? Pick up the right end of the keyboard and bang it down onto the desk top, HARD. This would usually jar the relay loose so it would work again, for awhile. A fellow in the Los Angeles area came up with the permanent fix. He cast a germanium transistor and a couple of resistors into a small potted shape (I think he used his refrigerator's ice cube tray for a mold) with two cables hanging out. One cord plugged into the cassette player, the other mated with the cable from the computer. This allowed the relay in the keyboard to switch only the base current of the transistor, and the transistor handled the motor current. This completely solved the sticking relay problem, and was cheaper than replacing the relay, to boot. I never did replace my sticking relay, it never stuck again!
Another curious accessory for the Model I (offered by Radio Shack) was the Screen Printer. This was a device which would give you a Polaroid-like snapshot sized copy of the screen image on a piece of aluminum foil coated paper, accompanied by a burning smell. The printer used an electric arc to selectively burn away the foil, leaving the black paper showing through. It did this remarkably rapidly, the whole print cycle requiring only about 3 seconds, if I remember correctly. The concept of the printer was remarkable, as it actually took control of your Model I away from the Z-80 and did a DMA scan of the screen memory of the Model I, then transferred control back to the Z-80. Because of the DMA scan, the "Screen Printer" port on the Model I is actually just the bus of the machine. Probably RS would not have made the bus accessible to us users if it had not been for the Screen Printer! However, the Screen Printer wasn't compatible with other devices, gave only a small piece of paper, and soon fell out of favor.
Another curiousity was the Exatron Stringy Floppy. This was a cassette tape drive using tiny cassettes which were endless loops. This scheme included a 1K ROM which was addressed into the Z-80 memory map where RS had left a blank area. If memory serves, the blank area in memory was 3000H to 37FFH, except for a few locations used by the printer and the floppy disk controller. To get started in the Exatron ROM, you did a CALL in BASIC to a location in the ROM. Because 3000H is 12288D, they put their entry point at 3045H, which was 12345D. You did a CALL 12345 in BASIC, and you were into the String Floppy system, Clever mnemonic!
Their Tape Operating System (TOS) linked with the Model I's ROM. Because their storage media (the tape) was endless, you had to go all the way around to load a program which you had just saved. No big deal, as the tape was short. The Exatron system died because the original tape cassette fabricator was a sole source, and when that company quit, no one else could produce usable cassettes, although Exatron made a valiant effort to find a second source.
I remember another cute piece of hardware by another vendor which occupied the same part of the unused memory map where EXATRON located their EPROM. This other piece of equipment was basically just a power supply, a 1K memory chip, and an address decoder. When activated, it provided a small monitor which could take over the machine and allow you to do research in and about the machine under control of the monitor instead of the RS ROMS. Since it was addressed to the same memory space as Exatron's EPROM, you could not have both in the machine simultaneously.
Another branch of the development of the Model I was by Holmes Engineering in Utah which built a sort of mother board/expansion interface, into which you plugged whichever accessory module you were interested in. I believe they offered memory, a clock, 8" drives, and I don't remember what all else. I think it was good equipment, but the market wasn't strong enough to support them. The name "Chipmunk" comes to mind as one of their product names, but I'm not sure of anything.
One of the complaints about the Model I, especially by owners of Apples, etc, was the multiplicity of wires and cables draped about a fully loaded Model I. It sure did take a lot of cable to interconnect everything! However, when I look at the back of a loaded IBM or clone these days, I feel right at home again. Wires all over the place! Oh, well.........
Some weird and wonderful aftermarket devices were created for the Model I. One of the less well-known arrangements was a board by a company named HUH Electronics which contained about a half dozen S-100 sockets. The intent was to allow use of S-100 boards on the Model I. The idea was not bad, as the HUH board plugged into the 40 pin Screen Printer socket, and tried to convert each bus over to the other, as required. The failing was that the clock line and some other important S-100 signals were not available on the 40 line TRS bus, and so any S-100 card requiring them had a problem.
A major name then, and still around, I believe, is Alpha Micro Technology. This outfit offers a motherboard and a line of accessory cards for it, including analog and digital I/O cards. Their relay cards can operate larger loads by means of the relay contacts. They had an interface card which would plug into their bus (named the A-Bus) and into the Model I, allowing the Model I to control whatever was plugged into the A-Bus. I am sure they have interface cards for other machines, including Apple, IBM, etc.
Alpha also offered a speech synthesizer. I remember a comment by a club member once that some one's speech synthesizer spoke with a Scandinavian accent, although I don't remember if it was Alpha Technology or Radio Shack's own Speech Synthesizer board! Yes, Radio Shack offered one, also.
Alpha also offered extension cords and cables of various sorts, such as floppy drive cables, hard disk cables, wye power cables to run two half height floppies on one power supply etc. They also offered the NEWCLOCK for the Models I, III and 4. This contained a clock chip and a small battery to keep it ticking when the computer was shut down. This avoided the need to answer the DATE and TIME question every time you booted up, and also put the correct time and date on your files.
Ever here of the Electric Crayon? It was an auxiliary board for the Model I which allowed you to create color images on a color monitor. I saw one once, but I don't know how it functioned. Must have had a block of memory plus a scanning circuit in it.
Another weird and wonderful device was a Rube Goldberg contraption which squatted on top of an electric typewriter, (most any brand), and by means of solenoids, struck the typewriter keys below it. This allowed any computer to interface with any electric typewriter, in theory. I once saw one driven by a Model I, and it ACTUALLY WORKED! Marvelous ingenuity to get it to function at all, but I hae me doots about its ultimate reliability.
Another problem was operation of CP/M, which was then big, on the Model I. At least two, maybe more companies created adapters for this purpose. One device was known as the Shuffleboard, which logically "shuffled" the TRS memory around in 16K blocks so CP/M could have RAM starting from 0000H, as required by CP/M. Another company, OMIKRON, offered a similar device which I bought, and which lived up to most of its promises. The most severe limitation was that only 48K of RAM was available, which did pinch a little as far as CP/M was concerned. But the device worked, and I enjoyed using it. OMIKRON also had a second adapter to allow the use of 8" floppies on the Model I, but I never tried it. Another source of CP/M for the Model I was Lifeboat Associates, who offered a modified form of CP/M which began loading at 4000H instead of 0000H, but this was incompatible with normal CP/M, and was very limiting to the user.
I also discovered another use for the OMIKRON mapper never intended by its manufacturer. The mapper had a 2K EPROM on board to give it enough intelligence to take control of the Model I at boot time, and also to contain the BIOS of the CP/M. By changing a jumper, I could prevent the EPROM from taking control, but could still engage it under control of RSM, a widely used monitor program of that time. Initially this just allowed me to disassemble the onboard EPROM to see how it was doing its tricks. The next step was to replace the OMIKRON EPROM with any 2K EPROM I wanted to read. Finally I figured out how to read a 4K EPROM in two halves by jumpering an address line. At about this time I bought an EPROM burner card for my IBM clone, and so have stopped playing with the OMIKRON mapper. But it was a useful tool in my learning process.
One of my friends, to this day, is making effective commercial use of two Model I's. He uses them to produce the paper tapes which control numerically controlled machine tools for his company. He keeps one Model I at work and has one at home, so if he has to take a problem home, all he carries is one floppy disk.
One of these machines is identified as a Model 1P (for portable); it is assembled with side brackets, a hinge, and a suitcase carrying handle. A couple of floppy drives are similarly packaged, so the whole machine is portable as two pieces of luggage, with only 3 cables to connect when he sets it up. Very effective and neatly done. We still see this machine at every monthly meeting of the San Gabriel Valley TRS User's Group, of which I was president in 1991.
The Model I can play music via a small addon board named Orchestra-80. This was a mono version, and later a stereo version identified as Orchestra-85 was offered. Still later there was an Orchestra-90 for the Models III and 4 and an Orchestra-90 CC for the Color machine. The Orchestra-90 produces fairly decent sounding music with up to 5 "voices" through an audio amplifier.
The radio amateurs developed an interface for the Model I which allowed it to transmit and receive frequency shift keyed (FSK) Morse code, presenting both the incoming and outgoing messages on the screen and saving them to disk files, if desired. This hardware worked well and was fairly popular. Considering the variability of incoming code (duration of dots, dashes and spaces) the software for this setup was really excellent.
Probably more different DOSes have been written for the Model I than any other machine that ever existed. I will list the ones I know of, although there are probably others.
TRSDOS came with the disk versions of the machine. Version numbers include 1.0, 2.0, 2.1, 2.2, 2.3, 2.3a, 2.7DD and 2.8DD. Version 1.0 was atrocious, unusable and short-lived. 2.0 was buggy and barely usable. 2.1 was better, but still buggy. 2.2 was a general cleanup of troubles, but included a new, fatal error of its own. It was so bad that 2.3 came out within a few days. I don't know 2.3a, but I have been told it is incompatible with 2.3. Art McAninch has discovered a V2.7S, single density that was released with a software program. This too seems incompatible with almost all else! 2.7DD and 2.8DD were double density DOSes, incompatible with all the foregoing.
A genius named Randy Cook was the author of the early versions, up through V2.3 if my rumors are correct. Randy gave TRSDOS its architecture and flavor, and it is really a great credit to Randy that our DOSes have so many nice features. Randy had a falling-out with Radio Shack, and went his separate way.
The Model II/12/16 family also had a DOS with version numbers 2.0 and 2.0a and also a TRSDOS 4.x series; these had nothing to do with the Model I, but the similarity of names sometimes led to confusion as to which was for what.
NEWDOS 2.1 was a cleaned-up version of TRSDOS V2.1 done by APPARAT, Inc, of Denver Colorado. Primarily it fixed up the errors of TRSDOS V2.1. NEWDOS+ was NEWDOS 2.1 with added utilities, including the famous Superzap. NEWDOS80 V1.0 was a completely rewritten DOS for the Model I. NEWDOS80 V2.0 was an improvement over NEWDOS80 V1.0, and is highly regarded and still used by many persons today, as a version of it was also written for the Model III.
There also were patches for NEWDOS 2.1 which made it into NEWDOS 77 for use with Percom's 77 track drives. My guess is the patches were by Percom.
There is also a NEWDOS80 V2.5 for both the Models I and III. These are the hard drive versions of NEWDOS80 V2.0. They consist of some additional files and an additional appendix and some ZAPS to the V2.0 manuals.
There are also versions of NEWDOS80 identified as NEWDOS86 and NEWDOS90 BY Warwick Sands in Australia. These exist in both Model I and III versions, and the latest version is being offered at the present time. Newdos80 and its successors was probably the most flexible DOS ever written (except perhaps MULTIDOS) when it came to configuring it for different floppy (and hard) disk formats. The most difficult thing about it was configuring it to read and write those selfsame formats. Many is the hour I have spent struggling with the rather terse manual, my machine and a strange disk, trying to make them all compatible. The formatting structure was controlled by the infamous PDRIVE command.
In fact, the PDRIVE was so difficult, especially if someone gave you a disk and didn't tell you what the PDRIVE was, that there was a real need for a routine to read the disk and determine what PDRIVE had been used to write the disk. I saw such a utility (called PDIR, if my memory is good) some years ago; Lance Wolstrup recently wrote another such device as a "finger exercises"! He writes good code just as easily as I drive a car. Phenomenal!
Art also has discovered a TRSDOS V3.0 for the Model I, apparently never officially released. It is single density, and when it boots up it, a title screen similar to V1.3 for the Model III appears on the Model I. Its commands and utilities are similar to V1.3 for the Model III, but the file formats are incompatible.
And now reenter Randy Cook! He brought out a DOS of his own and named it VTOS. In fact there was a VTOS 3.0 and a VTOS 4.0. Why 3 and 4? They were successors to TRSDOS V2, and so he simply went to 3 and 4 as the logical successors to TRSDOS V2.
Still another DOS was TRSDOS for the Model III. This DOS is not very compatible with anything, and has limitations such as single side only operation and no provision for hard drives. This went through V1.0, V1.1, 1.2, and 1.3. Still later, an aftermarket person developed it through V1.4 and 1.5. The V1.5 is now sold as SYSTEM 1.5 through TRS-Times, and now has the ability to operate double sided disks. It still has no hard drive capability, but otherwise is an excellent DOS. It also includes an Owners Manual, a rare feature these days! You have to print the manual from a file on the disk, but you do get a manual.
A DOS named DOUBLEDOS (DBLDOS) was written by Percom and was issued with or as a supplement to their doubler. Art has several versions of this DOS and also another Percom product named MICRODOS which is totally menu controlled from BASIC, and which he says gives you the feeling of operating an APPLE II. WHEE! Percom also offered an OS-80 at one time.
A company named LOBO International (I think) also developed an improved version of the Model I hardware named the MAX 80, and needed a DOS to go with it. Somehow this effort and a company named Galactic Software came together and the result was LDOS V5.x.
Later, Galactic Software became Logical Systems Inc., with Bill Schroeder and Roy Soltoff as two of the principals. There were other people, also, but I don't remember their names at this late date. Notice the Version number of LDOS, 5.x. It was the successor to Randy Cook's VTOSes, so up went the count. The Model III also received a version of LDOS, again with the V5 designation. LDOS went through version numbers 5.0.0, 5.0.1, 5.0.2, and 5.0.3 before it went to 5.1.0. From there it went through 5.1.1, 5.1.2, 5.1.3, and 5.1.4. The Model III version then went to V5.3.0 and lately 5.3.1. The Model I went from 5.1.4 directly to 5.3.1 to regain version number consistency with the Model III and 4 versions.
Still later, Radio Shack developed the Model 4, and needed a DOS for it. LSI produced LS-DOS (also known as TRSDOS) V6.x. This DOS for the Model 4 went through a number of upgrades, fixes and revisions, including V6.0, V6.1, V6.2, and V6.3, with 6.3.1 being the latest. All of these versions underwent minor revisions indicated by a third numeral. V6.2.1 was especially long-lived. LSI and MISOSYS, between them, put out versions of LS-DOS 6.2, 6.3 and 6.3.1 for the Model 2/12/16 family.
Another widely used DOS is DOSPLUS, done by Micro-Systems, Inc. in Florida, and it went through versions (that I know of) of V3.3, 3.4, 3.5 and 4.0 for both the Model I and Model III. They also had a version IV for the Model 4. Good DOSes, widely used and respected. The company was originally located in Hollywood FL and later moved to Boca Raton, where it may still be in business.
Another DOS still under sporadic development even today is MULTIDOS by Vern Hester. This DOS is known for its ability to automatically recognize and accommodate disk formats of almost every other Radio Shack DOS for the Models I, III and 4.
For further information on MULTIDOS and Vern Hester see Art McAninch's article "DOUBLE YOUR DENSITY? The Model I in Double Density, Part 2" in Computer News 80, Volume 4, Number 4, pages 4-6. In that article, Art relates the history of MULTIDOS, as told to him by David Welsh, the author of LazyWriter and a close personal friend of Vern Hester. MULTIDOS was a follow-on to ULTRADOS. ZDOS, MDOS, and LAZYDOS were all "kernels" of MULTIDOS. MULTIDOS 2.1 is still available for the Models I, III, and 4 from Alphabit Communications, Inc., Box 20067, Ferndale, MI 48220.
Art and I both have heard of SUPERDOS, but have no other information on it. Art would like a copy for his archives if anyone has it.
These are all the DOSes Art and I know about, but there may well be others!
Another area of interest is the software which was written for the Model I. Kim Watt, a well known genius in the Model I, III and 4 era wrote a marvelous utility known as SuperUtility which allowed editing of disks and memory on a byte, sector or other basis. It had the ability to copy much protected software (except itself!). It's major failing was its inability to access hard drives. Later, Kim brought out other versions of the program which could access hard disk files, known as Tool Belt and Tool Box. These and SuperUtility were all acquired by and are now available through MISOSYS.
An interesting trick developed by Kim Watt was his technique for writing both single density AND double density sectors on the same track of a disk at the same time. This allowed him to offer only one disk which would autoboot on either a Model I in single density or a Model III in double density. This allowed him to stock only one disk for both machines. A darn clever trick!