The IBM 1405 Disk Storage of 1960 used improved technology to double the tracks per inch and bits per inch of track -- to achieve a fourfold increase in capacity -- compared to the IBM RAMAC disk file of 1956.
Storage units were available in 25-disk and 50-disk models, for a storage capacity of 10 million and 20 million characters, respectively. Recording density was 220 bits per inch (40 tracks per inch) and the head-to-disk spacing was 650 microinches. The disks rotated at 1800 rpm. Data were read or written at a rate of 17.5K bytes a second.
The 1405 was used in conjunction with the IBM 1410 Data Processing System. Each 1410 was capable of controlling up to five of the 1405s, for a total of 100 million characters. In addition, a single 1405 of either model could be attached to an IBM 1401 Data Processing System.
The 1405 was reported to have been used with the "Walnut" information retrieval system of the U.S. Central Intelligence Agency in the 1960s. According to published reports, Walnut was the first mechanized system that could store and search millions of pages of documents.