to use a 2-wheeled "rolling module" in place of legs. First generation models (11x) ERS-110 The first commercially available AIBO, ERS-110 has a beagle-like appearance and was silver with a golden-brown hue and grey claws. There was a limited production of 5,000 units: 3,000 for Japan and 2,000 for the US market. Sales began on 1 June 1999 and sold out via the Internet in 20 minutes. It is often considered the rarest model of AIBO. ERS-110 cost 250,000 yen, or US$2,500, which would convert to over $3,500 as of 2020. ERS-111 The ERS-111 was released in November 1999 and was an improved version of the original AIBO marketed at the same price. It has a similar appearance to ERS-110, with different ear and tail shapes, and was available in metallic black or shiny silver with black claws. 40,000 units were manufactured. Second generation models (2x0, 31x) ERS-210 The ERS-210 was designed to look like a lion cub but was essentially a dog-shape with a flat bull terrier face and Jack Russell Terrier appearance, available in black, silver, gold, red, blue, green and white. It featured speech recognition capabilities and was the most popular AIBO model with over 65,000 units sold. It sold for around $1,500 at launch which was later reduced to less than $1,000. ERS-220 The ERS-220 had a more futuristic design based on a space exploration robot concept by Shoji Kawamori. It had a chrome finish with headlights and colored LEDs. Between 5,000 and 7,000 units were sold, priced at 180,000 yen. Remote operation was possible through an optional wireless local area network. Specifications: height 29.6 cm, 1.5 kg weight, 1.5 hours (default) continuous operation time, 2.5 hours or more operation with a re-celled battery, 16 degrees of freedom (drive unit). ERS-210A/220A Variants of ERS-210/220 with an improved CPU and head clutch. Nearly identical in appearance to the earlier models, they were distinguished by the Super Core logo on the underside of the body. US$1299 at launch. ERS-31x (Latte and Macaron) The ERS-31x models had an "AIBO's heart" slogan. The original production design illustrator was Katsura Moschino. The price was 98,000 yen or US$950. The "Latte" (ERS-311) is an off-white/cream color and is considered the "friendly" model. The "Macaron" (ERS-312) is mostly black with cream accents and is considered the "naughty" model. The "Pug" (ERS-31L) is the least common of the three and was $200 cheaper. The