The design of a mass memory for a database computer (DBC) is described. The DBC, a specialized back-end computer, is capable of managing 10∗∗9 to 10∗∗10 bytes of data and can support multiple data models with minimal software in the front-end computer. The design is based on moving-head disk technology which is perceived to be the most cost-effective technology for supporting such large volumes of on-line data. The design calls for certain key modifications in existing modes of disk component usage in an effort to incorporate a high degree of intelligence in the device and to enhance its throughput. These modifications pertain to activating concurrently all of the read/write heads available on an access mechanism and to the processing of data on-the-fly by associating a processing element with each read/write head.