An information storage system comprising an optical record carrier having a stack of information layers alternating with spacer layers, and a device for scanning the information layers, which device is provided with a radiation source and focusing means for selectively focusing a radiation beam from the radiation source on the separate information layers, characterized in that the focusing means introduce such a fixed, stack-associated spherical aberration in the radiation beam that this aberration compensates the spherical aberration incurred by the radiation beam when it is focused at approximately half the height of the stack of information layers. view more

An information storage system comprising an optical record carrier having a stack of information layers alternating with spacer layers, and a device for scanning the information layers, which device is provided with a radiation source and focusing means for selectively focusing a radiation beam from the radiation source on the separate information layers, characterized in that during reading the focusing means continuously introduces such a fixed, stack-associated spherical aberration in the radiation beam that this aberration compensates the spherical aberration incurred by the radiation beam when it is focused at approximately half the height of the stack of information layers. view more

An apparatus for reading from a track of a record carrier a digital signal which has been recorded thereon, the apparatus comprising: scanning means for producing a scanning spot which scans said track with a scanning velocity between 1.2 and 1.4 meters per second; read means for using the scanning spot to obtain from said track successive signal portions of a read digital signal which substantially corresponds to the digital signal recorded on said track; a buffer memory coupled to said read means for successively receiving therefrom and temporarily storing the signal portions, the signal portions stored in said buffer memory being subsequently read-out therefrom so as to produce an output digital signal; and control means for (i) interrupting storing of the signal portions in said buffer memory, and causing said scanning means to skip the scanning spot back to a previous track location and resume scanning therefrom, and (ii) resuming storing of the signal portions in said buffer memory when the scanning spot again reaches the track location at which scanning had previously been interrupted, interruption of storing of the signal portions in said buffer memory being such that the degree of filling therein is maintained within predetermined limits. view more

An apparatus for reading a data compressed digital signal from a track of a record carrier which has been recorded thereon, the apparatus comprising: scanning means for producing a scanning spot which scans said track with a predetermined scanning velocity; read means for using the scanning spot to obtain successive signal portions of a read digital signal having a read bit rate determined by the predetermined scanning velocity and substantially corresponding to the data compressed digital signal; a buffer memory coupled to said read means for successively receiving therefrom and temporarily storing the signal portions, the signal portions stored in said buffer memory being subsequently read-out from said buffer memory so as to produce an output digital signal; data decompression means coupled to said buffer memory for providing data decompression of the output digital signal; and control means for (i) interrupting storing of the signal portions in said buffer memory, and causing said scanning means to skip the scanning spot back to a previous track location and resume scanning therefrom, and (ii) resuming storing of the signal portions in said buffer memory when the scanning spot again reaches the track location at which scanning had previously been interrupted, interruption of storing of the signal portions in said buffer memory being such that the degree of filling therein is maintained within predetermined limits. view more