Star Gemini-10X

What the Star Gemini-10X was

The Star Gemini-10X was an 80-column, 9-pin serial impact dot-matrix printer sold by Star Micronics. Its user's manual - a combined "Gemini User's Manual" covering both the Gemini-10X and the wider-carriage Gemini-15X - classifies the machine as a "serial impact dot matrix" printer, and the Computer History Museum, which holds an example in its collection, dates it to around 1983 and records its place of origin as Japan. The Gemini line was built by Star Micronics Co., Ltd. of Japan and distributed in the United States by Star Micronics America, Inc. The printer formed characters on continuous fanfold paper, roll paper and single sheets, and offered a range of type styles, pitches and bit-image graphics selected by the host computer.

Print method: a 9-wire impact head

Like other impact dot-matrix printers, the Gemini-10X printed by driving thin wires from its print head against an inked ribbon to strike the paper, building each character from a grid of dots. Star's manual specifies a user-replaceable 9-wire (9-pin) head, with the pins thrust from the working side of the head against the platen-backed paper. Text printing was bidirectional and logic-seeking - the head printed in whichever direction reached the next line sooner - while dot graphics were printed unidirectionally. The standard character cell was a 9 x 9 matrix with true descenders, expanding to an 18 x 9 cell for emphasized print and 18 x 18 for double-strike output. This is the same general mechanism described in the overview of dot-matrix printing.

Speed, pitches and print modes

The manual rates the Gemini-10X at 120 characters per second at 10 characters per inch. Beyond the standard Pica pitch (10 cpi) it offered Elite (12 cpi) and Condensed (17 cpi), plus enlarged double-width printing at 5, 6 and 8.5 cpi, giving maximum line widths of 80 columns in Normal, 96 in Elite and 136 in Condensed. Additional modes included emphasized, double-strike, italic and super/subscript printing, continuous underline, and programmable horizontal and vertical tabs. These features were invoked through escape-code control sequences sent by the host computer, catalogued in the manual's function-code reference.

Graphics, character sets and downloadable characters

The Gemini-10X supported several bit-image graphics densities - 60 x 72, 120 x 144 and 240 x 144 dots per inch, described in the manual as low-, high- and ultra-high-resolution - together with 6 x 6 block graphics. Its character repertoire comprised 96 standard ASCII characters, 96 italic characters, 64 special characters, 32 block-graphic characters and 88 selectable international characters. The printer also allowed up to 96 downloadable, user-programmable characters, so custom glyphs could be defined and printed. A print buffer of 816 bytes was standard, with an option to expand it to 4K or 8K.

Paper handling, ribbon and interface

The Gemini-10X accepted fanfold paper 3 to 10 inches wide - one original plus up to two carbonless copies - as well as roll paper 8.5 inches wide (up to a 5-inch roll diameter) and single sheets 8 to 10 inches wide, advancing paper at about 10 lines per second at 1/8-inch spacing. It used a standard Underwood spool-type ribbon measuring 13 x 50 mm. The printer's standard connection was a Centronics-compatible parallel interface - a 36-pin connector using BUSY and ACK handshaking - and an RS-232C serial interface was available as an option. This Centronics-compatible parallel port let the printer attach to a wide range of contemporary personal computers.

Size, weight and power

According to Star's specifications, the Gemini-10X measured 392 x 315 x 148 mm (15.2 x 12.4 x 5.8 inches) and weighed 7 kg (15.4 lb); the Computer History Museum records its example at about 15 pounds. The printer ran from a region-dependent AC supply - 120 V at 60 Hz (about 1 A) or 220/240 V at 50/60 Hz (about 100 W). Star also quoted reliability figures of 5 x 10^8 lines mean cycles between failure (MCBF) excluding the print head, with a print-head life on the order of 10^8 characters.

Place in the early-1980s printer market

In the early 1980s, low-cost impact dot-matrix printers like the Gemini-10X were a mainstream choice for home and small-office computing, valued for inexpensive running costs, multi-part (carbon-copy) printing and broad software support through common control codes. The Gemini-10X sat below the daisywheel printers used for letter-quality correspondence, and well below the desktop laser printers that arrived mid-decade - such as the original HP LaserJet of 1984 - which offered far higher print quality at much higher cost. Within Star's own range, the Gemini-10X was the 80-column model, paired with the 136-column Gemini-15X that shared its manual and mechanism.

Documented specifications and reference scope

The figures on this page are drawn from Star Micronics' own Gemini-10X/15X user's manual and from the Computer History Museum's catalog record, and each specification is cited to its source. Where the manual gives separate values for the Gemini-10X and Gemini-15X, only the Gemini-10X figures are listed here. Values that cannot be traced to an authoritative record - including an exact market-introduction date or original list price - are omitted rather than estimated. This page is a historical reference, not a buying guide, and quotes no current pricing or availability.