Many VLSI floorplanners work by recursively decomposing rectangular modules into lower-level rectangular modules until the leaf-level modules are reached[5]. Good layouts require good floorplans. The quality of a floorplan depends (among other things) on how the leaf-level modules are clustered into the various levels of the hierarchy. Some of the factors that determine the suitability of a decomposition are the geometry of the modules, the connectivity among modules, and timing constraints. Our experience with the mechanization of a VLSI design manager[1] has shown that the initial structural hierarchy that arises during synthesis from behavioral specifications is not always suitable for floorplanning. We describe hierarchical-clustering-based algorithms that lead to a small number of superior candidate hierarchies.

We describe and prove correct a programming technique using a linked list of pages for managing the free disk pages of a file system where shadowing is the recovery technique. Our technique requires a window of only two pages of main memory for accessing and maintaining the free list, and avoids wholesale copying of free-list pages during a checkpoint or recover operation.

Experimental information-retrieval systems for telephone directory assistance and for filing office correspondence utilizing a superimposed-coded partial-match-retrieval scheme have been implemented. This extended-hash-code methodology permits the integration into the system of such user-oriented features as overlapping the query input and database search processes to give rapid apparent response, continual feedback to the user of the progress of the search, and abbreviation of keys by truncation. Simple coding and retrieval logic allow updating and rapid response to be achieved easily in either software or hardware realizations. The flexibility of the technique offers special advantages when casual users with fragmentary and ill-formulated queries need to approach a computerized information-retrieval system.