It was the first notebook-sized portable computer,[4][5] occupying roughly the footprint of an A4 notebook while being lightweight enough to hold comfortably with one hand at 1.6 kilograms (3.5 lb) and small enough to fit inside an average briefcase.

[8] It was announced in 1981 as the HC-20 in Japan,[1] and was introduced by Epson in North America as the HX-20 at the 1981 COMDEX computer show in Las Vegas, where it drew significant attention for its portability.

[2] Epson advertised the HX-20 with a photograph and photo editing of the computer on two facing magazine pages with the headline "Actual size".

[10] With a footprint about the size of a piece of A4 paper, the Epson HX-20 features a full-transit keyboard, rechargeable nickel-cadmium batteries, and a built-in 120 × 32-pixel LCD which allowed 4 lines of 20 characters.

It features a calculator-size dot-matrix printer, the EPSON BASIC programming language, two Hitachi 6301 CPUs at 614 kHz[11] which is essentially an enhanced Motorola 6801,[12] 16 kB RAM expandable to 32 kB, two RS-232 ports at a maximum of 4800 bits/s for the first 8-pin DIN connector intended for modem or serial printer with the second port capable of 38400 bits/s using a 5-pin DIN connector which was mainly for use with external floppy drive and video display[11] an early concept of docking station, a 300 bit/s acoustic coupler was available,[11] built-in microcassette drive, barcode reader connector.

[11] The HX-20 uses a proprietary operating system, which consists of the EPSON BASIC interpreter and a monitor program, and weighs approximately 1.6 kg.

BYTE in September 1983 wrote that the HX-20, available in the United States for about a year, had been unsuccessful because of the lack of software or accessories.

The review noted that Epson had included the formerly US$160 microcassette drive in the standard US$795 configuration, as well as bundling a simple word processor.

BYTE praised the printer as "nothing short of amazing", but criticized the lack of an operating system for cassette storage and said that compared to the TRS-80 Model 100's display, "the HX-20 looks primitive".

The Monitor program can be accessed via the main menu on startup by pressing 1, by typing the command "MON" in BASIC or by causing a trap, i.e. writing/reading to/from protected addresses or executing an illegal instruction.