The TRS-80 Model II is a computer system launched by Tandy in October 1979, and targeted at the small-business market.

It was announced in May 1979, deliveries began in October,[4] and only Tandy-owned Radio Shack stores sold the computer.

[6] 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 the high-speed (for the time) 4 MHz Z80A, DMA, vectored interrupts, a detachable keyboard with two function keys and numeric keypad, and port instead of memory-mapped I/O.

The Model II ran the TRSDOS operating system (renamed to TRSDOS-II starting with version 4.0) and BASIC.

Three internal expansion slots could be used for add-on cards such as additional serial ports and a video board that allowed bitmap graphics.

Like most capacitive keyboards, it utilized a key mechanism with foam rubber disks; these are prone to dry-rotting with age and requiring replacement.

The first revision models (1979–80) could not boot from a hard disk and the floppy controller required a terminating resistor pack for the last drive on the chain in place of the standard method of putting a terminating resistor pack on the internal disk drives.

The combined effect of the case fan and the floppy motor resulted in an extremely noisy computer compared to the nearly silent Model I/III.

This deficiency was rectified with the Model 12, which could accommodate up to 768 KB RAM using the newer 4164 DRAM chips and a revised bank-switching scheme.

Despite being designed primarily for business or operating factory equipment, the Model II did have a handful of games available; notably the Scott Adams Adventure series were offered for it.

In 1981, the 64K Model II computer was $3,350 and the "primary unit" 8.4 MB hard disk another $4,040 by mail-order from Radio Shack's dealer in Perry, Michigan; MSRP in the company's own stores was higher.

[13] Tandy produced and marketed various Model II business applications ranging from accounting, medical office, legal office, payroll, inventory, order entry, and sales analysis, to general-purpose applications for word processing, database management, and later spreadsheet work.

The Model 12 moved the Centronics and serial ports to a cluster on the rear left side of the computer.

TRSDOS-16 is a TRSDOS II-4.1 application providing a 68000 interface and support for up to three users, with no additional features and little compatible software.

[13] Tandy admitted that it should have encouraged third-party software development, which resulted in the killer app VisiCalc for the Apple II.

Tandy offered multi-user word processing (Scripsit 16),[27] spreadsheet (Multiplan), and a 3GL "database" (Profile 16, later upgraded to filePro 16+), as well as an accounting suite with optional COBOL source for customization.

An expansion board with 512 KB memory was offered for the 6000, raising the maximum total RAM to one megabyte.

The Model 6000 was referred to simply as the Tandy 6000 due to a marketing decision to move away from the Radio Shack and TRS-80 badges.

[30] In 1987, Tandy announced that the 6000 hardware would no longer be improved; customers believed that their systems had become orphaned technology.

[31] By 1988, Radio Shack had begun offering IBM-compatible 386 PCs for their professional line and finally retired the Model II family.

'"[2] BYTE's review in January 1984 stated that "the Model 16B is a fairly well-implemented and apparently well-supported Xenix system" that would likely receive much support from software developers.

The authors said that it greatly improved on the Model I and III, and surprised them by being a very good small Unix development system.

While criticizing Xenix's user unfriendliness for small business customers, and wondering "whether Radio Shack can or will invest" in training on the very sophisticated operating system for its dealers, they concluded that the Model 16B "deserves serious consideration".

[32] The magazine in August 1984 described the 16B as "a usable multiuser microcomputer system", but with a slow hard drive that might limit the computer to two users.