The first cassette machines (e.g. the Philips EL 3300, introduced in August 1963) were simple mono-record and -playback units. Early machines required attaching an external dynamic microphone. Most units from the 1980s onwards also incorporated built-in condenser microphones, which have extended high-frequency response, but may also pick up noises from the recorder motor.
A portable recorder format still common today is a long box, the width of a cassette, with a speaker at the top, a cassette bay in the middle, and "piano key" controls at the bottom edge. Another format is only slightly larger than the cassette, also adapted for stereo "Walkman" player applications. The markings of "piano key" controls soon were standardized, and are a legacy still emulated on many software control panels. These symbols are commonly a square for "stop", a vertically pointed triangle with a line under it for "eject", a right-pointing triangle for "play", double triangles for "fast-forward" and "rewind", a red dot for "record", and a vertically divided square (two rectangles side-by-side) for "pause".
The Sony Walkman, the "iPod" of the past
Walkman is a Sony brand tradename originally used for portable audio cassette/tape players in the late 1970s. In the 2010s, it was used to market Sony's portable audio and video players as well as a line of former Sony Ericsson mobile phones. The original Walkman actually introduced a change in music listening habits by allowing people to carry recorded music with them and listen to music through lightweight headphones. Owners of the Walkman were able to take back their "lost" time, commuting for example, and turn it into a pleasurable experience, or add a soundtrack to their urban surroundings. It was the privatization and personalization offered by the Walkman that led to its success.