Abstract: A cached DASD peripheral subsystem is operated in a so-called non-synchronous mode, that is, device operations are not synchronous to the host processor operations. A rate-changing buffer is interposed between the channel attachment for the host processor and the DASD, preferably having a storage capacity for one full DASD track of data. The rotational position for the data records being transferred in either direction, i.e., write or read, are kept in the rate-changing buffer to be kept with the record being transferred through the rate-changing buffer. Each time the peripheral subsystem supplies ending status to the host processor and all records to be transferred are retentively stored in DASD, a record control field and the rotational position of the last record transferred in a chain of commands being transferred the rotational position of such last record, its type, and other control data are stored in a control store separate from any cache directory or track directory in cache.

Abstract: The peripheral cache DASD subsystem is connected to predetermined host processors. A channel connection between the host processor and the peripheral subsystem has a much higher burst rate then the burst data transfer rate of a DASD while having an extended signal propagation time preventing rapid exchanges of interactive control signals. The branch write occurs in that data is written both to the DASD and to the cache simultaneously. The write domain is established in the subsystem by the host processor as a number of records to be written on the DASD only after the available cache space is compared with a needed cache space for the entire write domain. Whenever the available cache space is less than the write domain needs, then the peripheral cache DASD subsystem subsets the data transfer into a plurality of subset data transfers each having data storable in the available cache data storage space.

Abstract: Error control procedures are described for an optical disk recorder. High and low criteria for each of a plurality of machine operations or functions of an optical disk recorder are described. Such functions include erasing a sector, writing data, and reading data. Each function has two sub parts, reading a sector ID and performing the function in a data field. The high and low criteria for reading the sector ID and for performing the function in the data field, are different. The high and low criteria for a ROM portion of the optical disk are different from that provided for magnetooptic portion.