A method for detection of a sequential data stream which can be performed in a data storge subsystem without host computer intervention is disclosed featuring examination of the channel program processed during a read operation for signals indicative that the data is not part of a sequential data stream, for example, embedded seek instructions. If a particular channel program for does not contain such indications, the successive record or records may then be staged to a faster access memory device such as a solid-state cache. The invention is described in a plug-compatible, software-transparent configuration.

A multi-processor, multi-tasking virtual machine comprises processes, messages, and contexts. Processes communicate only through messages. Contexts are groups of related processes. The virtual machine is implemented in a distributed data processing system comprising a plurality of individual cells coupled by a local area network (LAN). Each cell may comprise one or more processes and/or contexts. A network interface module (NIM) provides the interface between any individual cell and the LAN. To facilitate message transmission between processes resident on different cells, each NIM is provided with tables identifying the locations of resident and non-resident processes, respectively. Cells may be added to or deleted from the LAN without disrupting the LAN operations.

An improved backup storage system and method for use in conjunction with hierarchical or mass storage servers and networks is disclosed. Baseline, full and incremental backup procedures are used to save file copies. In one preferred embodiment, the baseline backup procedure is used to store copies of stable files, i.e. files that are modified less frequently, if at all. With a hierarchical storage server, such files are typically those stored on tertiary storage media, e.g. erasable optical disks, WORMs or magnetic tape. The full backup procedure stores, as full backup copies, copies of all files not in the baseline backup and files that have been changed since the time of their baseline backup. The full backup procedure also stores file identifiers and signal representative of storage locations of baseline backup copies for files which have not been changed since the time of the baseline backup. The incremental backup procedure stores, as incremental backup copies, copies of files not in the baseline or full backups, e.g., new files, and files that have changed since the time of their last backup (baseline, full or incremental). The incremental backup procedure also stores file identifiers and signals representative of storage locations of baseline backup copies for files which have not been changed since the time of the baseline backup, and also stores file identifiers and signals representative of storage locations of full and incremental backup copies for files which have not been changed since the time of their full or incremental backup.

In a magnetic disk controller equipped with a cache memory for disks, the controller in accordance with the present invention includes high order paths for data transfer between a high order channel apparatus and the cache memory through a certain one of a plurality of channel adaptors, low order paths for data transfer between a low order device, e.g. a magnetic disk device, and the cache memory through a certain one of a plurality of device adaptors and a path for data transfer betweeen the low order device and the channel cevice without passing through the cache memory by selecting empty device adaptor and channel adaptor by the switching operation of a switch. When an interrupt is generated from the device, data transfer can be made easily even when the high order path and the low order path are busy, and path utilization efficiency can be improved.

A block substitution method of a cache memory incudes the steps of storing data integrity information with a main memory for each block of the cache memory and calculating a non-reference period of each block. The non-reference periods of the blocks are compared to determine an order of the blocks based on the non-reference periods and a difference between the non-reference period of the block having a longest non-reference period and the non-reference period of other blocks is calculated. Data integrity in the block having the longest non-reference period is examined and when there is no data integrity in that block the data integrity in other blocks is examined in the order of the non-reference period. A block having a longest non-reference period among the blocks having the data integrity is determined and the determined block is selected as a block to be substituted by a new data block when the difference is smaller than a predetermined value. New data is loaded to the selected block.