TRS-80 Model II
TRS-80 Model II
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| Manufacturer | Tandy Corporation |
|---|---|
| Type | Personal computer |
| Release date | October 1979 |
| Introductory price |
US$3,450 (equivalent to $11,385 in 2016) (32KB) US$3,899 (equivalent to $12,866 in 2016) (64KB) |
| Operating system | TRSDOS, Microsoft Basic |
| CPU | Z-80A @ 4.00 MHz |
| Memory | either 32 or 64k of RAM |
| Storage | singled-sided Shugart 500k 8" floppy drive |
| Display | 80x25 text |
| Input | detachable keyboard |
| Dimensions | 14 x 21 1/4 x 23 1/2 inch |
The TRS-80 Model II was a computer system launched by Tandy in October 1979, and targeted at the small-business market.
Despite its name, the Model II was not an upgrade of the original (Model I) TRS-80, but an entirely different system.
The Model II was succeeded by the compatible TRS-80 Model 12, Model 16 and Model 16B and the Tandy 6000.
Tandy saw businesses as the primary market for its computers. The Model II and its software were especially designed for such customers, and only Tandy-owned stores sold the computer. As a professional business machine, the Model II used state-of-the-art hardware and had numerous features not found in the primitive Model I such as DMA, vectored interrupts, a detachable keyboard, and port instead of memory-mapped I/O. It sported 80x25 text and a singled-sided 500k 8" floppy drive, and either 32 or 64k of RAM, along with two RS-232 ports and a Centronics-standard parallel port. The video memory could be banked out, so that the whole 64k address space could be used for main memory. Unlike most computers, it had no BIOS ROM except a small boot loader (the BIOS was loaded off the boot floppy). Because of this and the use of port I/O, almost all of the Model II's memory could be used by software. The Model II ran the TRSDOS operating system (renamed to TRSDOS-II starting with version 4.0) and BASIC. The different disk format and system architecture made it impossible to run Model I/III software on the Model II, thus it never had as much available. This was somewhat mitigated by the availability of the CP/M operating system for the Model II from third parties such as Pickles & Trout. Unlike the Model I/III, the Model II's memory map is compatible with standard CP/M. Three internal expansion slots could be used for add-on cards such as additional serial ports and a video board that allowed bitmap graphics.
BASIC was provided on disk rather than in the system ROMs, partially to give the Model II a more professional and less of a home-computer appearance. The Model II BASIC was similar to Level III Disk BASIC on the Model I/III, but had cassette support removed and incorporated several enhancements from the then-latest version of Microsoft BASIC-80, which included enhanced string-handling features, an improved editor, octal number conversion, and error-trapping. On the downside, the PEEK and POKE commands were removed from Model II BASIC which made it less hacker-friendly. However, if CP/M was used, the user had access to MBASIC for CP/M which was very similar to Model II BASIC and did allow PEEK/POKE.
The floppy drive included with the Model II was a Shugart SA-800 full-height, single-sided 8" drive; like most such drives, it spun continuously whether the disk was being accessed or not and the spindle motor was powered directly off the A/C line. The floppy controller in the Model II was a double-density, soft-sector unit based on the WD 1791 floppy controller. Although the Model II otherwise used double-density (MFM) diskettes, TRSDOS OS disks utilized a single-density (FM) boot track. CP/M distros did not use FM boot tracks. CDC drives were used for the floppy expansion module.
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