HP ThinkJet (2225, 1984)

What the HP ThinkJet was

The HP ThinkJet was a personal inkjet printer introduced by Hewlett-Packard in 1984 under the model number 2225. Its name abbreviates "Thermal Ink Jet," the drop-on-demand technology it used to form characters and simple graphics. The HP Computer Museum records a launch price of US$495 and a resolution of 192 × 96 dpi at 150 characters per second. HP positioned the machine as a compact, low-cost printer for the individual computer owner, emphasizing quiet operation and low power consumption rather than the impact printing of the era's dot-matrix machines.

The first HP "Jet" and a mass-market inkjet

Hewlett-Packard's own virtual museum describes the ThinkJet as "the first mass-marketed personal inkjet printer." The HP Computer Museum separately records it as the first HP printer to carry the "Jet" name — a convention HP later applied to product lines such as QuietJet, PaintJet, DeskJet, LaserJet, OfficeJet, ScanJet and JetDirect. These are attributed manufacturer and museum claims about HP's own product history; the ThinkJet was not the first inkjet device ever built, and this page does not assert that broader superlative.

How thermal inkjet printing worked

The ThinkJet used thermal inkjet printing, in which tiny resistive heating elements in the printhead rapidly boil a thin layer of ink to form a vapor bubble; the expanding bubble ejects a droplet through a nozzle onto the page. HP's account traces the technique to an engineer studying how a thin silicon-based film responded to electrical stimulation, who found that the superheated medium expelled droplets of the fluid beneath it. Because the mechanism needs very little power and can be manufactured inexpensively, HP was able to package it into a small, affordable printer. The general operation of this print method is covered in the account of thermal inkjet printing.

Documented specifications

Authoritative records agree on the core figures. The HP Computer Museum and Wikipedia list a resolution of about 192 × 96 dpi and a print speed of 150 characters per second, and the HP Computer Museum records a US$495 launch price. Contemporary and museum accounts single out the ThinkJet's quiet operation as its defining practical benefit. Figures that cannot be traced to an authoritative manufacturer, museum or archive source — such as a precise nozzle count, ink-cartridge capacity or a discontinuation date — are omitted here rather than estimated.

Interface variants (2225A–2225D)

The ThinkJet was sold in several variants distinguished by their host interface and power arrangement. The HP Computer Museum documents the 2225A with an HP-IB interface and internal mains supply, the 2225B with an HP-IL interface and a rechargeable battery, the 2225C with a Centronics parallel interface and internal mains supply, and the 2225D with a serial (RS-232-C) interface and external power. The HP-IL/battery variant reflected HP's interest in portable, instrument-style computing during this period.

Place in printing history

The ThinkJet marked HP's entry into consumer inkjet printing and established the branding and low-cost, low-noise design approach that HP carried into the later DeskJet line. HP framed the technology as a quieter, more capable alternative to the inexpensive serial dot-matrix printers that dominated the low end of the market. Alongside the LaserJet, which appeared the same year and shared the "Jet" name, the ThinkJet is documented as one of the products that shaped HP's imaging and printing business through the following decades.

Practical limitations and reference scope

Contemporary and later technical accounts note that early ThinkJet output worked best on specially coated paper, and that its printheads added an ongoing consumable cost — trade-offs typical of first-generation consumer inkjet hardware. This page records only facts that can be traced to an authoritative source (manufacturer, museum or archive records); any specification that cannot be sourced is omitted rather than guessed. It is a historical reference, not a buying guide, and quotes no current pricing or availability. The sources consulted are listed below.