Sony Corporation

Other

Teruo Chiba

Atsushi Takeuchi

Shinichiro Kato

Mineo Moribe

Sakuya Tamada

Takehiko Numata

Tadao Igarashi

Yasuaki Nakane

Shuichi Igarashi

Susumu Sakamoto

In a rewritable optical recording medium, a recording surface is divided into a plurality of zones by setting pitch intervals in the radial direction to be constant and a data area and a spare area for a defective sector are allocated in each zone. As for a capacity of the spare area in each zone, a predetermined total capacity of spare areas is allocated so that a spare ratio K&equals;D /D of a capacity D of the spare areas for a capacity D of the data areas becomes almost the same in the zones.

Spare area with a predetermined capacity for a detective sector allocated in each zone

A magneto-optical disk having a four-layer structure formed of a first protective dielectric layer, a recording magnetic layer, a second protective dielectric layer and a reflective metal layer is disclosed. The constraints for the film thicknesses of the various layers are determined not only from the optical and magneto-optical aspects, but from the aspect of the dynamic thermal response. The recording magnetic layer is a magnetic layer mainly formed of TbFeCo and having a film thickness of not less than 180 .ANG. and not more than 280 .ANG.. The first protective dielectric layer is a nitride film having a film thickness such that the product of its refractive index and the film thickness is not less than 0.2 and not more than 0.35 times the wavelength of the laser light employed. The second protective dielectric layer is a nitride film having a film thickness such that the product of its refractive index and the film thickness is not less than 0.1 and not more than 0.15 times the wavelength of the laser light employed. The the reflective metal layer is a metal layer having a film thickness of not less than 500 .ANG. and not more than 1000 .ANG., with the metal being electro-chemically less noble than the material of the recording magnetic layer and having a reflectivity at the boundary with the second protective dielectric material of not less than 70%.

Magneto-optical disk

A tape cassette for use with a video tape recorder has conventional tape guiding and braking elements within its housing, including a pair of spaced guide pins for the tape adjacent each reel and a resilient strip that acts on the tape between the spaced guide pins and normally tends to deflect the tape from a straight path between the spaced guide pins for braking the tape when the cassette is not in use. A drag member is provided that contacts the tape when it is deflected to provide a tortuous path for the tape and thereby increase the resistance to tape movement.

VTR tape cassette

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Miyagi, Japan

Teruo Chiba