Two years after the CD's home debut, Sony shrank the format down dramatically with the D-50 (sold as the D-5 in some markets), released in 1984 — the first portable CD player. It took real engineering effort to make a laser-read optical disc format work reliably in something you could carry around, and the D-50 became the foundation for what Sony would later brand the Discman line, extending the personal-listening concept the Walkman had established five years earlier to the new digital format.
Even so, most CD listening in 1984 was still happening on home component systems rather than on the go — portable CD players remained a genuine novelty at this point, and it would take further price and size reductions before they became a mainstream choice the way the cassette Walkman already was.