Editing TRS-80 (section)

=== Model III ===
{{anchor|modeliii}}{{Infobox information appliance
| name = TRS-80 Model III
| image = TRS-80 Model 3 01.jpg
| caption = 
| logo = 
| developer = 
| manufacturer = [[Tandy Corporation]]
| carrier = 
| family = 
| type = [[Home computer|Home and small business computer]]
| generation = 
| release date = {{Start date and age|1980|07}}
| lifespan = 
| price = {{ubl|$699 (4KB RAM, Level I)| $999 (16K, Level II)| $2495 (48K, two 180 KB floppy drives, RS-232C)<ref>{{cite web |title=1981 Radio Shack Computer Catalog RSC-4 pages 5-6 |url=https://www.radioshackcatalogs.com/flipbook/c1981_rsc-04.html?fb3d-page=05 |website=radioshackcatalogs dot com |publisher=Tandy/Radio Shack |access-date=May 21, 2019}}</ref>}}
| discontinued = {{End date and age|1983|09}}
| os = TRSDOS 1.3, LDOS 5<ref>{{cite web |title=Radio Shack Computer Catalog RSC-8 page 40 |url=https://www.radioshackcatalogs.com/flipbook/c1983_rsc-08.html?fb3d-page=40 |website=radioshackcatalogs dot com |publisher=Tandy/Radio Shack |access-date=December 2, 2022}}</ref>
| cpu = [[Zilog Z80A]] @ 2&nbsp;[[MHz]]
| memory = 4 [[Kilobyte|KB]] or 16, 32 or 48 KB
| display = 16 rows by 64 or 32 columns, block graphics
| graphics = optional 640 by 240 pixels, $369 extra<ref name="RSCatalog-08-1983">{{cite web |title=Radio Shack Computer Catalog RSC-8 page 52 |url=https://www.radioshackcatalogs.com/flipbook/c1983_rsc-08.html?fb3d-page=52 |website=radioshackcatalogs dot com |publisher=Tandy/Radio Shack |access-date=December 2, 2022}}</ref><ref name="TRS80Mod3HiResGraphicsManual1982">{{cite book | url=https://archive.org/details/TRS-80_Computer_Graphics_1982_Tandy | title=TRS-80 Computer Graphics | publisher=Tandy Corp. | date=1982}}</ref>
| sound = output through cassette port
| compatibility = Model I  Z80 code ~ 80% (higher with patches), BASIC 100%
| predecessor = Model I
| successor = [[TRS-80 Model 4|Model 4]]
}}
Tandy released the '''TRS-80 Model III''' on July 26, 1980. The improvements of the Model III over the Model I include:<ref>{{cite web|title=1981 Radio Shack Computer Catalog RSC-4, pg. 5|url=https://www.radioshackcatalogs.com/flipbook/c1981_rsc-04.html?fb3d-page=05|website=radioshackcatalogs dot com|publisher=Tandy/Radio Shack|access-date=December 2, 2022}}</ref> built-in lowercase, a better keyboard with repeating keys, an enhanced character set, a real-time clock, 1500-baud cassette interface, a faster (2.03&nbsp;MHz) Z80 processor, and an all-in-one enclosure requiring fewer cables. A Model III with two floppy drives requires the use of only one electrical outlet; a two-drive Model I requires five outlets.<ref group="note">One outlet each for the CPU/keyboard, Expansion Interface, Video Monitor, and the drives.</ref> The Model III avoids the complicated power on/off sequence of the Model I. Shortly after the Model III's introduction, Model I production was discontinued as it did not comply with new [[Federal Communications Commission|FCC]] regulations as of January 1, 1981, regarding [[electromagnetic interference]].{{r|hogan19810831}}{{r|hoganm319810831}}<ref name="robertson198012">{{cite magazine |url=https://archive.org/stream/80-microcomputing-magazine-1980-12/80Microcomputing_1280#page/n49/mode/2up |title=Model I Caught By FCC Fallout |access-date=March 21, 2011 |author=Robertson, Nancy |date=December 1980 |magazine=[[80 Micro]] |issue=12 |pages=51, 56}}</ref>{{r|newsletter_8101}}{{r|white198708}}

Tandy distinguished between the high-end Model II{{r|freibergerfuture19810831}} and Model III, describing the former as "an administrative system, good for things like word processing, data management and VisiCalc operations" and suitable for small businesses.{{r|freiberger19810831}} The lowest-priced version of the Model III was sold with 4 KB of RAM and cassette storage. The computer's CPU board has three banks of sockets (8 sockets to a bank) which take type 4116 DRAMs, so memory configurations come in 16 KB, 32 KB, or 48 KB RAM memory sizes. Computers with 32 KB or 48 KB RAM can be upgraded with floppy disk drive storage. There is space inside the computer cabinet for two full-height drives. Those offered by Tandy/Radio Shack are single-sided, 40-track, double-density (MFM encoding) for 180K of storage. Third-party suppliers offered double-sided and 80-track drives, though to control them they had to modify the TRSDOS driver code or else furnish an alternative third-party DOS which could (see below). The installation of floppy disk drives also requires the computer's power supply to be upgraded. There is no internal cooling fan in the Model III; it uses passive convection cooling (unless an unusual number of power-hungry expansions were installed internally, such as a hard disk drive, graphics board, speedup kit, RS-232 board, etc.).

Tandy claimed that the Model III was compatible with 80% of Model I software.{{r|freiberger19810831}} Many software publishers issued patches to permit their Model I programs to run on the Model III. Marketing director Ed Juge explained that their designers considered changing from the Model I's 64-column by 16-row video screen layout, but that they ultimately decided that maintaining compatibility was most important.<ref>{{cite magazine |last1=Juge |first1=Ed |magazine=[[80 Micro]]|pages=10–11 |title=Inside 80 |url=https://archive.org/details/80-microcomputing-magazine-1980-09/page/n9 |issue=9 |publisher=CW Communications |access-date=May 22, 2019|date=September 1980}}</ref>

The Model III's memory map and system architecture are mostly the same as the Model I's, but the disk drives and printer port were moved from memory mapped to port I/O, thus Model I software that attempts to manipulate the disk controller directly or output to the printer (in particular Model I DOSes and application packages such as Visicalc and Scripsit) will not work. Under the supplied TRSDOS 1.3 operating system Model I disks can be read in the Model III, but not vice versa.{{r|hogan19810831}} The optional LDOS OS (by Logical Systems Inc.) uses a common disk format for both Model I and Model III versions.

Customers and developers complained of bugs in the Model III's Microsoft BASIC interpreter and TRSDOS.<ref name="freiberger19810831">{{cite magazine |url=https://books.google.com/books?id=rD0EAAAAMBAJ&pg=PA49 |title=Bugs in Radio Shack TRS-80 Model III: How Bad Are They? |access-date=February 28, 2011 |author=Freiberger, Paul |author-link=Paul Freiberger |date=August 31, 1981 |magazine=[[InfoWorld]] |volume=3 |number=17 |page=49}}</ref> Tandy/Radio Shack (and TRS-80 magazines like ''[[80 Micro]]'') periodically published many software patches to correct these deficiencies and to permit users to customize the software to their preferences.

Differences in the WD1771 and WD1791 floppy controllers created problems reading Model I disks on a Model III (the double-density upgrade in the Model I included both chips while a Model III had only the WD1791). The WD1771 supports four data markers while the WD1791 only supports two, and some versions of TRSDOS for the Model I also use them. In addition, they are used by copy protection schemes. Software was available to allow Model I disks to be read on a Model III. The WD1791 supports the 500-bit/s bitrate needed for high-density floppy drives, but the controller is not capable of using them without extensive modifications.

TRSDOS for the Model III was developed in-house by Radio Shack rather than being contracted out like the Model I's DOS. None of the code base from Model I DOS was reused and the Model III DOS was rewritten from scratch; this also created some compatibility issues since the Model III DOS's API was not entirely identical to the Model I DOS. This was primarily to avoid legal disputes with Randy Cook over ownership of the code as had occurred with Model I DOS and also because Radio Shack originally planned several features for the Model III such as 80-column text support that were not included. Two early versions, 1.1 and 1.2, were replaced by version 1.3 in 1981 which became the standard Model III OS. TRSDOS 1.3 is not format compatible with 1.1 and 1.2; a utility called XFERSYS is provided which converts older format disks to TRSDOS 1.3 format (this change is permanent and the resultant disks cannot be read with the older DOS versions).

The Model III's boot screen was cleaned up from the Model I. Instead of displaying garbage on the screen at power up, it displays a "Diskette?" prompt if a bootable floppy is not detected. The user can insert a disk and press any key to boot. On powerup or reset holding down the {{key press|Break}} key will boot the computer into ROM-based Level II BASIC. This ability is useful if the disk drive is not functioning and cannot boot a TRSDOS disk (or if a boot disk is not available); it permits an operator familiar with the machine hardware to perform diagnostics using BASIC's PEEK and POKE commands. This works for the Model 4 as well, but not for the 4P.

While Model I DOS is fairly flexible in its capabilities, Model III DOS is hard-coded to only support 180K single-sided floppies, a problem fixed by the many third-party DOSes. To that end, when Radio Shack introduced hard disks for the TRS-80 line in 1982, the company licensed LDOS rather than attempting to modify Model III DOS for hard disk support.

Level II BASIC on the Model III is 16 KB in size and incorporates a few features from Level I Disk BASIC.

TRSDOS 1.3 was given a few more minor updates, the last being in 1984, although the version number was unchanged. This includes at least one update that writes an Easter Egg message "Joe, you rummy buzzard" on an unused disk sector, which is reputedly a joke message left by a programmer in a beta version, but accidentally included in the production master.<ref>{{Cite web|url=http://www.trs-80.org/trsdos-rummy-buzzard-release/|title=The TRSDOS "rummy buzzard" release|website=www.trs-80.org}}</ref>

The Model III keyboard lacks {{key press|CONTROL}}. Many application programs use {{key press|@}}, while others use {{key press|SHIFT|Up}}. Often {{key press|CLEAR}} is used in combination with number and alpha keys. The Model III keyboard also lacks {{key press|CAPS LOCK}}; to caps-lock the alpha keys the user presses {{key press|SHIFT|0}}. Under LDOS [[typeahead]] is supported.

Because TRSDOS 1.3 was found wanting by many users, Tandy offered (at added cost) Logical System's LDOS Version 5 as an alternative. As with the Model I, other third-party sources also offered TRSDOS alternatives for the Model III, including NewDOS, Alphabit's MultiDOS, and Micro Systems Software's DOSPlus. These are compatible with TRSDOS 1.3 and run the same application programs, but offer improved command structures, more and better system utilities, and enhancements to the Microsoft BASIC interpreter. After writing the original Model I TRSDOS, Randy Cook began work on his own DOS, titled VTOS, which was superseded by LDOS and also created some frustration for users as it is the only TRS-80 DOS to be copy-protected.

Although mostly intended as a disk-based computer, the Model III was available in a base cassette configuration with no disk hardware and only 16 KB of RAM with Level II BASIC. Radio Shack also offered a 4K version with Level I BASIC, identical to Model I Level I BASIC, but with the addition of LPRINT and LLIST commands for printer output. Upgrading to a disk machine necessitates installing at least 32 KB of RAM, the disk controller board, and another power supply for the disk drives. Disk upgrades purchased from Radio Shack included TRSDOS 1.3; users upgrading from third-party vendors had to purchase DOS separately (most opted for LDOS or DOSPlus), though a great many Model III applications programs included a licensed copy of TRSDOS 1.3.

As with the Model I's E/I, the RS-232C port on the Model III was an extra cost option and not included in the base price of the computer, though the dual disk Model III for $2495 included the serial port.

Like the Model I, the Model III sold well in the educational market. Many school administrators valued the Model III's all-in-one hardware design because it made it more difficult for students to steal components.{{r|white198708}} ''InfoWorld'' approved of the Model III's single-unit design, simplified cable management, and improvements such as lack of keyboard bounce and improved disk reliability. The reviewer, a former Model I owner, stated "I'm impressed" and that "had the Model III been available, it's probable that I wouldn't have sold it". He concluded, "If you're looking for a computer that's not too expensive but that performs well, you would be wise to test the Model III—you might end up buying it."{{r|hoganm319810831}}

Don French, who had left Radio Shack to found FMG Software after designing the Model I, expressed his disappointment in the new machine while trying to convert CP/M to run on it. "I've encountered numerous problems with the floppy drive and its interface. Radio Shack will sell a Model III to anyone. They're trying to market it as a business computer when the existing software is woefully inadequate. 48K just isn't enough. You run out of memory before you get going. They're selling a medical package that takes up nine disks. I think the Model III is a very poorly conceived machine".{{r|freiberger19810831}}

==== Aftermarket products ====
Aftermarket hardware was offered by Tandy/Radio Shack and many third-party manufacturers. The usual selection of add-ons and peripherals available for the Model I were offered: outboard floppy drives (one or two could be plugged into a card-edge connector on the back panel), an outboard hard disk drive (LDOS was furnished as Tandy's hard drive OS vice TRSDOS), an RS-232C serial port on an internal circuit card, and a parallel printer (connected by a card-edge connector). Multiple high-resolution graphics solutions were available.<ref name="ReedHighResGraphics"> { {cite web | url=http://www.trs-80.org/high-resolution-graphics-for-the-trs-80/ | title=High-resolution grpahics for the TRS-80 | author=Reed, Matthew | access-date=Oct 26 2024 } }</ref>  The official Radio Shack Model III high-resolution graphics board had a screen resolution of 640 x 240 pixels.{{r|RSCatalog-08-1983}}{{r|TRS80Mod3HiResGraphicsManual1982}}  The third-party Micro-Labs "Grafyx Solution" board had a screen resolution of 512 x 192 pixels.<ref name="Dyk198301"> { {cite magazine | url=https://archive.org/stream/80-microcomputing-magazine-1983-01 | title=The Grafyx Solution (Review) | access-date=Oct 26 2024 | author=Dyk, Harley | date=January 1983 | magazine=[[80 Micro]] | issue=1 | pages=65-69 } }</ref>
A popular hardware/software add-on was the Orchestra-90<ref>{{cite web|title=Orchestra-90|url=http://www.trs-80.org/orchestra-90/|website=trs80 dot org|publisher=Matthew Reed|access-date=May 3, 2017}}</ref><ref>{{cite web|title=1985 Radio Shack Computer Catalog RSC-12, page 31|url=https://www.radioshackcatalogs.com/flipbook/c1985_rsc-12.html?fb3d-page=31|website=radioshackcatalogs dot com|publisher=Tandy/Radio Shack|access-date=December 2, 2022}}</ref><ref>{{cite magazine |last1=Ludwig |first1=Gary A. |title=Let There Be Music |magazine=[[80 Micro]] |date=March 1985 |page=114 |url=https://archive.org/details/80_Micro_1985-03_CW_Communications_US/page/n115/mode/2up|publisher=CW Communications |access-date=July 9, 2020}}</ref> music synthesizer. It can be programmed to play up to five voices with a range of six octaves stereophonically. A great many Orch-90 (as it was often called) music files were available for download from [[CompuServe]]. The Orch-90 was licensed from a company called Software Affair, which also produced the Model I-compatible Orchestra-85 from 1981.

At least three vendors produced CP/M modifications for the Model III, Omikron (also a Model I mod), Holmes Engineering, and Memory Merchant.<ref>{{cite magazine |last1=Kepner |first1=Terry |magazine=[[80 Micro]] |date=December 1983 |title=CP/M III Ways|page=122 |url=https://archive.org/details/80-microcomputing-magazine-1983-12/page/n121/mode/2up |publisher=CW Communications |access-date=July 17, 2020}}</ref> Options were available for upgrading the [[Cathode-ray tube|CRT]] to the CP/M professional standard of 80 columns and 24 rows, as well as eight-inch floppy drives.

A number of third-party manufacturers specialized in upgrading Model IIIs with high-performance hardware and software, and remarketing them under their own labels.<ref>{{cite magazine |magazine=[[80 Micro]] |pages=81–94 |title=The Muscle Micros, These Three Sleek Supercharged Model IIIs... |url=https://archive.org/details/80-microcomputing-magazine-1983-04/page/n81 |access-date=May 22, 2019|date=April 1983}}</ref><ref group="note">It was necessary to rebrand these highly modified Model IIIs because Radio Shack enforced a strict policy that no repair service would be performed on nonstandard RS products.</ref> The improvements typically included internal hard disk drives, greater capacity floppy drives, 4&nbsp;MHz Z80 speedup kits, professional-grade green or amber CRT video displays, better DOS software (typically DOSPlus by Micro Systems Software or LDOS by Logical Systems) including the all-important hard drive backup utilities, and custom menu-driven shell interfaces which insulated non-expert users (business employees) from the DOS command line. These were touted as high productivity turnkey systems for small businesses at less cost than competing business systems from higher-end providers such as IBM and DEC, as well as Radio Shack's own [[TRS-80 Model II]].