The next major development in multitrack recording came in the mid-1950s, when the Ampex corporation devised the concept of 8-track recording, using its "Sel-Sync" (Selective Synchronous) recording system, and sold the first such machine to musician Les Paul. However, for the next 35 years, multitrack audio recording technology was largely confined to specialist radio, TV and music recording studios, primarily because multitrack tape machines were both very large and very expensive – the first Ampex 8-track recorder, installed in Les Paul's home studio in 1957, cost a princely US$10,000 – roughly three times the US average yearly income in 1957, and equivalent to around $90,000 in 2016. However, this situation changed radically in 1979 with the introduction of the TASCAM Portastudio, which used the inexpensive compact audio cassette as the recording medium, making good-quality 4-track (and later 8-track) multitrack recording available to the average consumer for the first time. However, by the time the Portastudio had become popular, electronics companies were already introducing digital audio recording systems, and by the 1990s, computer-based digital multitrack recording systems such as Pro Tools and Cubase were being adopted by the recording industry, and soon became standard. By the early 2000s, rapid advances in home computing and digital audio software were making digital multitrack audio recording systems available to the average consumer, and high-quality digital multitrack recording systems like GarageBand were being included as a standard feature on home computers.