Many file and database management systems are implemented using fixed-length physical records on movable head discs. Such implementation not only causes internal dependence among different components of the file access time, but also induces an external dependence of the overall access time on request input rate. Accordingly, conventional performance estimates are inaccurate here, and the error in using them typically ranges from 10% to 100+% for different loading conditions. This paper presents revised formulae for calculating the file response time, throughput and busy period for such a storage structure. The analysis makes use of the Takács process in queueing theory.