TRS-80 Model I/III/4:
Frequently Asked Questions

Here are a few frequently asked questions on the Radio Shack TRS-80 Model I, Model III, and Model 4. These are Z-80 based machines that were first introduced in 1977. The three models were partly compatible with one another, and incompatible with most everything else. Today they are of interest only to the nostalgic and a few folks who have specialized applications that were never ported to newer machines. The following are questions that people frequently ask me; your mileage may vary! This FAQ is available on the Web through the page http://www.research.digital.com/SRC/personal/Tim_Mann/trs80.html.

Contents


[1] Where can I get TRS-80 software and hardware?

Most software from Misosys, Logical Systems, Galactic Software Ltd., Powersoft, and Breeze/QSD is now available for free download by permission of the copyright owner, Roy Soltoff (owner of Misosys). See http://www.research.digital.com/SRC/personal/Tim_Mann/trs80.html.

Other sites with downloadable software include:

Computer News 80 has some commercial software and hardware products, a library of freeware disks, and a small monthly newsletter that still supports the TRS-80 I/III/4. You can contact them via the Web at http://www.computernews80.com/, via email at compnew@trib.com, or by phone at 307-265-6483.

M. A. D. Software deals in TRS-80 products. Among other things, they have upgrades to the Model 4P ROMs and the MODELA/III file (Model III ROM image). Web pages are in preparation, but for now, you can contact them via email at madcs@madsoft.lonestar.org or via US mail at:

M. A. D. Software
P. O. Box 331323
Fort Worth, TX 76133-1323

Frank Gottschalk (``The TRS-80 Recycler'') deals in used TRS-80 hardware and software. You can contact him at 72623.40@CompuServe.COM.

Archive Software is a small venture run by Cord Coslor. Cord buys and sells used TRS-80 Model I/III/4 software and hardware (among other things). See his Web page at http://www.geocities.com/SiliconValley/Vista/4395/archive.html or contact him at archive@navix.net.

Pete Bumgardner trades in old TRS-80 hardware and software. See his ``TRS-80 Again'' Web page at http://www.simology.com/trs80again/ or email him at trsorder@simology.com.

If you live in the San Francisco Bay area, you can try WeirdStuff Warehouse. They specialize in old computer hardware and software, and occasionally have some TRS-80 stuff in the back. See their Web page at http://www.weirdstuff.com.

You can still order some software from Tandy Software Replacement and/or Radio Shack Unlimited, formerly Radio Shack National Parts. You can ask at a store or call Radio Shack at 800-843-7422. I'm told that you might have to bug people for a while and maybe ask for a supervisor or someone who's been there longer, before you find someone who believes this is possible and knows how to do it. The purpose of Tandy Software Replacement is to supply replacement disks to people whose originals have been destroyed, so generally they do not provide manuals or packaging, and the prices are very low. They don't actually seem to care whether you originally owned the software. Radio Shack Unlimited also stocks (or can make up) full packages of some software, including manuals.


[2] Where can I get information to repair or upgrade my TRS-80?

You might find a little information on the Web, but pickings are slim for hardware information. You can start with the TRS-80 links on my Web page, at http://src-www.pa.dec.com/~mann/trs80.html#links.

You can ask on the newsgroup comp.sys.tandy. This is a good place for TRS-80 software questions too. You might also try searching back postings to the group with Deja News.

Also try the sources given in topic [1] to see if they carry hardware manuals. Tandy Software Replacement or Radio Shack Unlimited are said to be able to photocopy and sell manuals, but I haven't tried this.

Computer News 80 has a mail-in repair service; see topic [1].

Tandy Repair Centers may or may not be able to fix your TRS-80. There is some danger that they won't know how to find the necessary parts and information. They don't see a lot of these machines any more!


[3] What TRS-80 emulators do you recommend?

People don't really ask me this, but I need to put this information somewhere to refer to from other answers!

Under MS-DOS or MS Windows, I recommend:

Under Unix, I recommend the xtrs Model I/III/4 emulator, version 2.0 or later. This is freeware, available from http://www.research.digital.com/SRC/personal/Tim_Mann/trs80.html. It should work on any version of Unix with the X Window System, except that its support for physical floppy disk drives works only under Linux.


[4] What is a .DSK file?

A .DSK file is an image of a TRS-80 floppy disk in a file. They are used by TRS-80 emulators.

Warning: There are two kinds of .DSK files with different formats, one that originated with Jeff Vavasour's Model I emulator and one that originated with his Model III/4 emulator. Each of Jeff's emulators works only with the kind of .DSK file that was designed for it. Matthew Reed's Model I/III emulator and the xtrs Model I/III/4 emulator work with both kinds of .DSK file transparently.


[5] How can I convert my real TRS-80 floppy disks to .DSK files?

One way is to transfer data over the TRS-80's serial port or printer port. That's probably the best way if you have a Model I, because a stock Model I can read and write only single density, but many PCs cannot deal with single density (see topic [11]). Jeff Vavasour's Model I emulator includes instructions on how to do this; see topic [3].

A faster and more convenient way, if you can get it to work, is to read the disks in a PC with a 5" floppy drive. Under MS-DOS or MS Windows, try Matthew Reed's freeware READDISK program. See http://www.arrowweb.com/mkr/readdisk_doc.html.

Alternatively, if you have problems with READDISK or you are using Linux, you can copy the disks with an emulator, as follows.

  1. Get a TRS-80 emulator that supports both .DSK files and real floppy drives. See topic [3]. Read the emulator's instructions and get it running.
  2. Find a PC with a real 5" floppy drive attached. In theory, a 40-track DD drive is best if your TRS-80 had 40-track or 35-track drives, but you can use 80-track HD drives too. (On a PC, 40-track DD drives are usually called 180KB or 360KB drives, depending on whether they are single or double sided.) The trouble with this theory is that DD drives may not work with some emulators, and if your DD drive is a pullout from a TRS-80, you may have difficulty cabling and jumpering it correctly for a PC.
  3. Configure the emulator with an LDOS or other operating system .DSK file as drive :0, a new, empty .DSK file as drive :1, and the real drive as drive :2. If you are using a Model I emulator with LDOS, note that Model I LDOS comes on two .DSK files, so configure the emulator with the second one (LDOSXTRA.DSK) as drive :3.
  4. Boot the emulated machine. Model I LDOS requires an extra driver to deal with double density, so if you are using it, type FDUBL to the emulator after booting.
  5. Put the floppy into the real drive and copy it to the emulated drive (.DSK) file. If you are using LDOS 5.3.1, the command is QFB :2 :1. On LS-DOS 6.3.1, the command is DISKCOPY :2 :1. Both those commands format the floppy automatically. On non-LDOS systems, the command might be COPY or BACKUP, and you might need to give extra command line options and/or to FORMAT :1 first; I can't help on that. You might also be able to copy disks by running SuperUtility or the like under the emulator, although programs like SuperUtility have problems running on some emulators.

[6] How can I convert .DSK files to real TRS-80 floppy disks?

There are at least three possibilities:

(A) One way would be to transfer data from your newer computer to a real TRS-80 through its serial port or printer port. That may be the only way if you have a Model I, because a stock Model I can read and write only single density, but many PCs cannot deal with single density (see topic [11]). However, I don't know of any software for transferring data to the TRS-80 through a serial or parallel port.

(B) A faster and more convenient way, if you can get it to work, is to write the disks in a PC with a 5" floppy drive. Here is a procedure you can follow.

  1. Get a TRS-80 emulator that supports both .DSK files and real floppy drives. See topic [3]. Please don't say, ``But I don't need an emulator, I have a real machine!'' You need an emulator to run this procedure, and they are nice to have anyway, so get one.
  2. Get the files working for you in the emulator as .DSK files. Read the instructions for the emulator to find out how to do this.
  3. Find a PC with a real 5" floppy drive attached. In theory, a 40-track DD drive is best if your TRS-80 had 40-track or 35-track drives, but you can use 80-track HD drives too. (On a PC, 40-track DD drives are usually called 180KB or 360KB drives, depending on whether they are single or double sided.) The trouble with this theory is that DD drives may not work with some emulators, and if your DD drive is a pullout from a TRS-80, you may have difficulty cabling and jumpering it correctly for a PC.
  4. Bulk-erase a 5" floppy, preferably using an AC bulk tape eraser as sold by Radio Shack and others. You may be able to omit this step if you are using a 40-track drive, but it's a good idea to do it anyway. It is best to use floppies that are rated for double density or quad density, not high density. High density floppies will work in a pinch, but don't expect double density data to stay stable on them for a long time.
  5. Configure the emulator with an LDOS or other operating system .DSK file as drive :0, the .DSK file you want to convert as drive :1, and the real drives as drive :2. If you are using a Model I emulator with LDOS, note that Model I LDOS comes on two .DSK files, so configure the emulator with the second one (LDOSXTRA.DSK) as drive :3.
  6. Boot the emulated machine. Model I LDOS requires an extra driver to deal with double density, so if you are using it, type FDUBL to the emulator after booting.
  7. Put the floppy into the real drive and copy the emulated drive (.DSK) file to it. If you are using LDOS 5.3.1, the command is QFB :1 :2. On LS-DOS 6.3.1, the command is DISKCOPY :1 :2. Both those commands format the floppy automatically. On non-LDOS systems, the command might be COPY or BACKUP, and you might need to give extra command line options and/or to FORMAT :2 first; I can't help on that. You might also be able to copy disks by running SuperUtility or the like under the emulator, although programs like SuperUtility have problems running on some emulators.
(C) If you need a copy of LS-DOS 6.3.1 on a real floppy and have no other way to do it, M. A. D. Software will make a diskette for you for $7.50 US plus shipping. Paper documentation is included. You can request a single-sided or double-sided floppy. This service was announced on 19 January 1998. See topic [1] for contact information.

[7] How can I get individual files off a .DSK file or TRS-80 floppy disk?

Most of the TRS-80 emulators have programs for doing this. Read the instructions for your emulator to find out how to use them. Sometimes the program runs on the emulated Z-80 (a /CMD file); other times it runs on the host operating system (an .EXE file).

Under Jeff Vavasour's Model I emulator, the relevant program is VREAD.EXE. Under Jeff's Model III/4 emulator, it is EXPORT/CMD. Under Matthew Reed's Model I/III emulator, the program is TRSREAD.EXE and is available only with the registered version. Under xtrs, the program is called EXPORT/CMD (not the same program as Jeff's).


[8] How can I put individual files onto a .DSK file or TRS-80 floppy disk?

Most of the TRS-80 emulators have programs for doing this. Read the instructions for your emulator to find out how to use them. Sometimes the program runs on the emulated Z-80 (a /CMD file); other times it runs on the host operating system (an .EXE file).

Under Jeff Vavasour's Model I emulator, the relevant program is VWRITE.EXE. Under Jeff's Model III/4 emulator, it is IMPORT/CMD. Under Matthew Reed's Model I/III emulator, the program is TRSWRITE.EXE and is available only with the registered version. Under xtrs, the program is called IMPORT/CMD (not the same program as Jeff's).


[9] What do I do with TRS-80 software that comes in .ZIP files?

Some TRS-80 software you will find on the Web is supplied in .ZIP archive files. You need to unzip these files to unpack their contents, and you'll generally need to do this on your PC or Unix box, not your TRS-80 (or emulated TRS-80). You can get free unzip programs from http://www.cdrom.com/pub/infozip/.

Within some .ZIP archives is a .DSK file. This is an emulated floppy disk file. See topic [4] and the rest of this FAQ for instructions on how to deal with .DSK files.

Other .ZIP archives contain individual files extracted from TRS-80 disks. You can use these with an emulated (or real) TRS-80 by copying the files onto a .DSK file or a real floppy. See topic [8] for instructions.

Some .ZIP archives of TRS-80 software may contain both a .DSK and the individual files extracted from it. This is perhaps the most convenient form, but obviously takes up twice as much space as either of the others.


[10] What are the system file passwords on LDOS, LS-DOS, and TRSDOS 6?

The table below is based partly on documentation and partly on actual test. Where a filename matches more than one pattern, use the first one that matches. If a password doesn't work, try others from the table and let me know of the error. If you have password information for other Model I/III/4 operating systems, let me know.

Files        LDOS 5.1    LDOS 5.3.1    TRSDOS 6      LS-DOS 6.3.1
-----        --------    ----------    --------      ------------
basic/*      (unused)    basic         basic         basic
lbasic/*     basic       (unused)      (unused)      (unused)
config/sys   ccc         ccc           ccc           ccc
*/sys        wolves      system        lsidos        system6
*/flt        gsltd       filter        filter        filter
*/dvr        gsltd       driver        driver        driver
*/dct        rrw3        driver        utility       driver or utility
*/cmd        rrw3        utility       utility       utility
*/hlp        (unused)    help          (unused)      help
back door    rs0lt0ff    rs0lt0ff      (nflag$ bit7) (nflag$ bit7)
The password listed as ``back door'' gives you access to all files regardless of what their real passwords are. It's documented! I confirmed by looking at the source code that TRSDOS/LS-DOS 6 has no such password, but I found that later versions of it have another, undocumented back door: if you turn on bit 7 of NFLAG$, all file password checking is disabled. The command MEMORY (A="N", B=128) will do this. This back door can be found in TRSDOS 6.2 and LS-DOS 6.3.1, but not in TRSDOS 6.1.2. I'm not sure exactly when the */sys password in TRSDOS/LS-DOS 6 changed from lsidos to system6.

[11] What problems do PC floppy disk controllers have with TRS-80 disk formats? What problems do different TRS-80 models have with each other's disk formats?

The Western Digital 177x/179x floppy disk controllers that were used in TRS-80s have some capabilities that PC disk controllers generally lack. The executive summary is that (1) most standard PC floppy controllers can't handle single density at all, (2) even those that can handle single density generally cannot read the directory track on a Model I TRSDOS disk, and (3) there can also be problems reading double density disks. Here are more details.

Many PCs cannot handle single density (FM) encoding. The original Model I used single density exclusively, and even a Model I with a double density adaptor requires a single density boot sector on system disks. The original IBM PC controller required extra outboard components to support clock/data separation for single density, but IBM left them off to reduce their manufacturing costs. (So I'm told; I wasn't involved with PCs in that era.) This started the tradition of leaving out single density support in PCs. Modern PCs use more highly integrated IO chips that include data separation on the chip, but many still omit single density support. I have experience with the National Semiconductor PC87306, which supports single density (though the chips are no longer tested and certified to work in single density mode), and the Intel 82078, which does not support single density at all. I'd welcome information about other chips to add here.

The WD1771, used in the TRS-80 Model I, is able to read and write single-density sectors with nonstandard data address marks (DAMs) 0xF9 and 0xFA, as well as the standard ones 0xFB (data) and 0xF8 (deleted data). The WD1791/1793 and later chips, used in the Model III and 4, can read all such sectors, but cannot distinguish between 0xFB and 0xFA, or 0xF9 and 0xF8. Model I's with double density adaptors have *both* controllers, and use the 1771 for single density, so they are fully compatible with stock Model I's. PC disk controllers, even those that do single density, cannot read sectors that use the 0xFA or 0xF9 DAM at all. (I have actually tested this only with 0xFA on a PC87306. I'd welcome corrections if other standard PC controllers can handle these data address marks.)

These differences would be no problem if Model I software did not actually use the nonstandard DAMs, but unfortunately, it does. In particular, Model I TRSDOS 2.x distinguishes between normal data sectors and directory sectors by using 0xFB for the former and 0xFA for the latter. On Model III/4 TRSDOS-like systems, where 0xFA is not supported, the distinction between 0xF8 and 0xFB is used instead. Some later Model I systems (such as LDOS 5.0.2 and later) also switched to 0xF8 on the directory to allow for direct media compatibility with the Model III/4, while others stuck with 0xFA for direct Model I TRSDOS compatibility. Patches for TRSDOS 2.3 were developed that allow it to read and/or write 0xF8 directory sectors, but they were not widely used. Special software is supplied with Model III/4 operating systems that allows them to read Model I disks and/or convert them to Model III/4 format. (The REPAIR command on LDOS is an example of the latter.) No such software can work on a PC controller, however, because the 0xFA sectors cannot be read at all.

There are also many gratuitous format differences amongst the various TRSDOS-like TRS-80 operating systems. For most of the systems, a single-density, single-sided, 35-track disk is a common denominator, except for the DAM problem just discussed. Adding more tracks is usually not a problem, though some systems may insist that the directory remain on track 17, while others put the directory location in track 0, sector 0, byte 2. The various systems diverged in the way they generalized the format to work with double density and other larger drives. The main streams were LDOS, NEWDOS, and Model III TRSDOS 1.3. LDOS uses a variable number of sectors per granule (allocation unit) that must evenly divide the number of sectors per track, and uses exactly one cylinder for the dirctory. I believe NEWDOS always uses 5 sectors per allocation unit, but allows varying the packing of granules onto the disk and the number of granules used for the directory. Model III TRSDOS 1.3 made a large number of unnecessary changes to the format; it was clearly inspired by the Model I format, but it is not a compatible extension.

Many PC disk controllers have difficulty reading double density disks formatted by older releases of TRS-80 operating systems, even with the proper software on the PC. Many TRS-80 operating systems formatted the disks with too short a gap between the index hole and the first sector. I'm told that you can sometimes work around this problem by putting a piece of tape over the index hole. The WD1770 controller used in later releases of the TRS-80 Model 4/4P hardware also had problems reading these disks, so later releases of all the Model III and 4 operating systems were corrected to format floppies with the proper gap lengths.

Add-on floppy controller cards for the PC that are specifically intended for disk duplication or for converting disks from other kinds of machines often use Western Digital chips or custom hardware that is more versatile than standard PC controllers. For example, the Catweasel controller (see http://members.tripod.com/~apd2/catweasl.htm can be programmed to handle just about any format. I've heard people mention the MicroSolutions CompatiCard, too, but the CP/M FAQ says that it is a discontinued product, so you'd have to find a used one somewhere.


[12] What are the differences among single, double, quad, and high density floppy media?

There is essentially no difference between single and double density media (if you can actually find any single density media anymore). Double density media has been tested and certified for double density recording, which is slightly more demanding than single density recording; conceivably, a dropout that might not be noticed in single density could be a problem in double density. In practice, though, I suspect that back in the days when manufacturers sold both DD and SD media, the media came off the same production line and the SD media would have met the DD standard nearly all the time.

"Quad density" 5" media is essentially the same too. It's certified for double density recording at 80 tracks per side rather than 40 tracks per side. Ordinary double density media usually works fine at 80 TPS, however. All 3.5" media is certified for 80 TPS.

You will also sometimes see media labelled as one-sided or two-sided. Both types have magnetic material on both sides, but on the disks advertised as one-sided, the second side may not have been tested. It's even possible, though unlikely, that the second side was tested and failed. Also, occasionally you'll find a "flippy" 5" disk. Such a disk can be recorded on both sides by removing it from the drive and flipping it over. It has two separate write-protect notches and two separate index hole cutouts in the jacket. Sometimes users would make their own flippy disks with a hole punch.

"High density" media is very different, and should not be interchanged with single/double/quad density media. It has different magnetic properties. You will usually not even be able to format DD media as HD, and although you can sometimes format HD media as DD and write to it, that's not a good idea. The media will be too strongly magnetized by the DD head and bleed-through can occur, garbling your data either right away or after the disk has sat on the shelf for a while. You can distinguish between 3.5" HD and DD media by looking for a hole in the jacket on the opposite edge from the write-enable hole; HD media has the extra hole, while DD media does not. You can usually distinguish between 5" HD and DD media by looking for a hub reinforcing ring; usually DD media has a ring and HD media does not, but not always.


** End of TRS-80 Model I/III/4 FAQ **