Posts in the “Expansion Interfaces” Category

The Microtronix Expandable Interface

The Microtronix Expandable Interface was probably the first third-party alternative to the Radio Shack Expansion Interface for the TRS‑80 Model I. It cost $129.95 when it was introduced in late 1978 by Microtronix of Philadelphia, Pennsylvania. According to the product announcement in H&E Computronics, the Expandable Interface was also available in kit form for around $100.00.

The Exatron MM+

The Exatron MM+, also known as the Exatron Memory Plus Expansion, was an alternative to the Radio Shack Expansion Interface for the TRS‑80 Model I. It was designed and sold by Exatron of Sunnyvale, California for use with their floppy disk storage alternative, the Exatron Stringy Floppy. Despite the fact that it was barely advertised and seems to have been only sold briefly in 1981, the Exatron MM+ remains one of the best remembered Expansion Interface alternatives.

The Microtek MT-32

By itself, the TRS‑80 Model I was capable of only limited expansion. In order to add memory beyond 16K and support floppy disk drives, Radio Shack sold an external device they called an Expansion Interface.

The Expansion Interface could expand memory to 48K, add a parallel printer port, and add a disk controller for connecting floppy disk drives. But an Expansion Interface with 32K of memory cost $597.00, almost $100 more than a 4K Model I.

The Holmes Expansion Mainframe

The Holmes Expansion Mainframe was a popular alternative to the Radio Shack Expansion Interface for the TRS‑80 Model I. Introduced in mid-1982, the Expansion Mainframe offered expansion options in a different manner than its competition. It provided extra features through the installation of special plug-in modules, also sold by Holmes Engineering.

The Lobo LX‑80 Expansion Interface

The LX‑80 was an alternative to the Radio Shack Expansion Interface that took a different approach to compatibility than the competition. It was originally announced by Lobo Drives International in Fall of 1979, but problems with the supplied operating system meant that it wasn’t released until closer to 1981. The original price was $799 (without memory), although that price had been reduced to $510 by late 1982.

The Micromint Disk-80 Expansion Interface

The Disk-80 was an alternative to the Radio Shack Expansion Interface that was sold by Micromint Inc. It was designed by Steve Ciarcia and was featured in his “Ciarcia’s Circuit Cellar” column in the March 1981 issue of Byte.

The LNW System Expansion

The LNW System Expansion was a popular alternative to the Radio Shack Expansion Interface. Introduced in 1979 by LNW Research, the System Expansion was the most popular of the Expansion Interface replacements. LNW Research later described themselves as “the number one manufacturer of system expansion units and accessories for the Model I computer”.

The LNW System Expansion sold for $69.95 as a kit with a bare printed circuit board and manual. LNW later introduced the $399.

The Radio Shack Expansion Interface

The Radio Shack TRS‑80 Model I had few options for internal expansion other than adding a maximum of 16K of internal memory. The external expansion possibilities were reserved for a device Radio Shack called the Expansion Interface.

The Radio Shack Expansion Interface plugged into the back of the Model I using a six-inch long cable and was designed to serve as a base for the TRS‑80 monitor.