Abstract: In a horizontal recording medium, new information can be overwritten upon old information at a low recording density without erasing the medium. In a perpendicular recording medium, on the other hand, new information is recorded at a high recording density after having erased the medium. On the basis of the above features of the horizontal and perpendicular recording mediums with different recording densities, the apparatus comprises first magnetic head with a long gap for the horizontal recording medium, a second magnetic head with a short gap for the perpendicular recording medium, and a heat selector, in order to provide a magnetic recording and reproducing apparatus compatible with both high and low recording density mediums.

Abstract: A multi-format optical disk recording/reproducing system in which data can be recorded in either of two formats having different data capacity. Both error correction and detection codes and synchronizing signals are recorded. However, the synchronizing signals are recorded with different intervals in the two formats.

Abstract: In an apparatus for recording and/or reproducing an information signal, such as, a PCM (pulse-code modulated) signal and the like, in slant tracks on a recording tape by means of rotary heads, and in which, when an index signal is recorded in, or erased from an area adjacent a part of a slant track in which the PCM signal is recorded, an index area signal which specifies the area for recording or reproducing the index signal is formed on the basis of address data in the reproduced PCM signal. Therefore, the index signal area always has a predetermined positional relation to a recording area of the PCM signal so that when the index signal is recorded in or erased from the index signal area, erasure of the adjacent PCM signal is prevented.