Designing File Systems— Direct Access
Graham John · 2018
Direct access devices, sometimes referred to as random access devices, include magnetic drums, magnetic card files, exchangeable disc stores, and fixed disc stores. The systems analyst rarely has the opportunity to design the record keys that his system will operate upon because these matters are often determined by the previous history of the organization, its products, and procedures. The index tables are often maintained on the direct access device, to reference the keys of transaction records to the buckets where the relevant main records are stored. A seek area is an area of storage which can be searched without physical movement of the read/write head across the surface of the discs. Eventually the buckets in the overflow area may become full, and the file has to be reorganized so that a larger storage area is allocated to the file; once more file growth is anticipated in setting the packing density.