The recording format of professional audio recorders has to be considered not only from the error correction point of view but also from the realization of such functions as overdubbing and tape cut editing. At first this paper describes the characteristics of errors which occur in the stationary-head type multi-track high density magnetic recording channel. The effect of fingerprints is also examined. The data shows that a two-dimensional code is effective for correcting the errors because of the nature of the error. Among two-dimensional codes, product code is selected from the stand point of code efficiency and hardware size. As a sub-class of generalized product codes, a code which is a combination of the Reed-Solomon code and the cyclic redundancy check code (CRCC) has been employed. In order to save the data recorded in an erroneous track the Reed-Solomon code is applied across the track and the check bits tracks are provided beside the audio data tracks. The data forms a frame in a track. The frame begins with a frame syncronization code, and is ended by the check bits of the CRCC. The optimum frame length concerning the redundancy and interleaving method of the data is described. The experimental data shows that the error correcting scheme is satisfactory.

Small-scale video on demand system will be necessary in the future. Cluster drives, which use optical disk drives, are a good buffer memory for this purpose because the cost per megabyte is low. An ordinary optical cluster drive has many SCSI buses and up to seven optical drives are connected to each SCSI bus. One drive from each bus is assembled to make a group of a cluster drive. The difference betweeen SCSI bus data transfer rate and sustained disk transfer rate enables the cluster drive to be simplified. Several drives on an SCSI bus make a sub-group. The video data is striped onto those sub-groups. When the total data transfer rate from disks within a sub-group exceeds the bus transfer rate, some drives can not acquire the bus. When drives connected to one SCSI bus are not identical, the block size of the data to be recorded on each drive has to be adjusted so that the maximum effective data transfer rate can be obtained. When the cycle times of a slow and fast drive are set identical, the effective data transfer rate is maximum, where one cycle consists of command time, minimum bus free time, disk read time, and bus transfer time.