History (1991): Data Storage Hierarchy According to IBM

Following is an excerpt of a patent and a SCSI interface (≠4974156) filed by Warren Harding, Robert Tennison and William Vomaska, all of them from IBM Corp.

The name of the patent is: “Multi-level peripheral storage hierarchy with independent access to all levels of the hierarchy.”

This text gives a good idea on IBM’s future position on this major subject. Let’s notice that this hierarchy only involves magnetic and optical disk drives. Magnetic tapes are not even mentioned.

Here is the excerpt: “A peripheral storage hierarchy includes 3 storage levels. The top storage level is a fast accessing direct access storage device(s), such as magnetic disk drives. The intermediate level is an automatic warehouse type library, storing a large plurality of optical disks, which are automatically transferred between storage cells of the library and optical disk drives operatively connected to the host processor. The bottom level of the storage hierarchy includes one or more stand-alone optical disk drives and a shelf unit. Personnel manually carry the optical disks between the standalone drives and the shelf unit upon mount and demount commands received from the host processor. The intermediate library level uses the same type of optical disk as used in the bottom level of the storage hierarchy. An I/O station in each of the automatic libraries enables manual access to the optical disk for transferring the optical disks between the intermediate and bottom levels. Preferably, the transfer is only from the intermediate level to the bottom level. Access to named storage objects in disks stored in the bottom level are through the standalone drives. A host processor has an independent access path to each level of the storage hierarchy. A directory and other data structures indicate the number of copies made of each named data object and the location of such copies, such that the host processor can independently access a copy from any level of the data storage hierarchy. “

This article is an abstract of news published on the former paper version of Computer Data Storage Newsletter on issue 44, published on September 1991.