Abstract: Turntable (10) has a turntable bottom (19) and a turntable wall (20) which together define a locating space (21) in which the hub (7) of an information disc is engageable, and in which it is centered by means of a centering member (12) and clamped by magnetic clamping means. At the circumference of the locating space a centering wall (26) is provided, which wall has an inwardly sloping surface (27). The dimensions of the various parts, the field strength of the magnetic means and the coefficients of friction of the cooperating materials of the hub and the turntable are selected in such a way that, once an information disc has reached a position in which the free end of the centering member (22) has engaged the centering hole (17) of the information disc, the outer wall (28) of the hub (7) is situated above the sliding surface (27) of the turntable.

Abstract: The recording surface of an optical record carrier (1) is divided into a succession of first (A) and second (B) annular zones, each including a plurality of substantially concentric information tracks. The tracks in each zone (A) include radially aligned first control words (13) and the tracks in the annular zones (B) include radially aligned second control words (14), the structures of the first and second control words being distinguishable from each other. An optical scanning device projects a beam which as it scans the tracks reads the control words and a detection circuit generates a measurement signal V.sub.m upon each passage of the beam from one zone to another. The measurement signal can be utilized to rapidly address the scanning beam to any of the annular zones.

Abstract: An information-transmission system including an encoder for converting n-bit information words (D7, . . . , D0) into transmitted m-bit code words (C10, . . . , C0), and a decoder which reconverts the received code words (C'10, . . . , C'0) into information words (D*7, . . . , D*0) corresponding to the original information words. For a first group the encoder converts a first portion (D7, . . . , D3) into a first portion of a code word, such portion comprising q bits (C10, . . . , C5) thereof; and converts a second portion (D2, . . . , D0) of the information word into a second portion of the code word, such portion comprising s bits (C4, . . . , C0) thereof. For a second group the encoder converts a first portion (D7, . . . , D3) into a second portion comprising q bits (C'5, . . . , C'0) of a code word, and converts a second portion (D2, . . . , D0) of the information word into a first portion comprising s-bits of (C'10, . . . , C'6) such code word.

Abstract: Method of providing a substrate of an optically readable information disc with an optically detectable structure, mould for use in the method, apparatus for carrying out the method, and information disc manufactured in accordance with the method.Substrate (3) is provided with a disc hub (8) comprising disc-centering means (9) which serve to center the finished information disc (17) on the drive spindle (27) of a drive apparatus. The intermediate product comprising the substrate (3) and the disc hub (8) is centered on the base (1A) of the mould by cooperation between the base-centering means (17) and the disc-centering means (9). This may be effected by the use of an auxiliary centering means (12) which is in contact with a wall (14) of a central centering hole (11) in the disc hub (8) and with a wall (13) of a central centering recess (10) in the base (1A).

Abstract: The invention relates to a method of providing a substrate with a centered optically detectable structure, such as a servo structure on a transport substrate of an optical information disc. The method uses a mould (1) having a base (1A) carrying a mould structure (2) which is covered with a reproduction layer (4) of a transparent radiation-curable resin, which after curing is detached from the mould together with the substrate. In its center the base (1A) of the mould is provided with base-centering means (7) relative to which the mould structure is centered accurately. Before it is placed on the mould a substrate (3) is provided with a disc hub (8) comprising separate disc-centering means (9) which serve to center the finished information disc (17) on the drive spindle (27) of a drive apparatus. The intermediate product comprising the substrate (3) and the disc hub (8) is centered on the base (1a) of the mould by cooperation between the base-centering means (17) and the disc-centering means (9).

Abstract: An interchangeable optically readable storage disk has a substrate with a recording surface, and a cover thereon which may comprise a second substrate with a further recording layer. The disk includes a protecting arrangement at the circumference of the substrate, which includes a balancing arrangement. The balancing may be effected by apertures in the protecting arrangement, or balancing masses affixed thereto.