From an IBM press release, 1956 | IBM History.
The 650 RAMAC and 305 RAMAC both utilize the magnetic disk memory device announced as experimental by IBM a year ago. Both machines are the first of a planned line of equipment designed for high-volume, in-line processing of business data. Transactions are processed continuously, as they occur, instead of being held until a group is accumulated, sorted and batch processed. In a single step, all records affected by a transaction will be immediately adjusted to account for the change.
The 650 RAMAC combines the IBM 650 Magnetic Drum Data Processing Machine with a series of disk memory units which are capable of storing a total of 24-million digits. The 305 RAMAC is an entirely new machine which contains its own input and output devices and processing unit as well as a built-in 5-million-digit disk memory. Both machines operate according to a program of electronically stored instructions.
An advanced feature of the new continuous accounting machines is the method by which the memory may be interrogated. With the 650 RAMAC, typewriter operators at remote inquiry stations may “ask” the machine for any of the data in the vast memory. Instants later the answer — perhaps a sales total or an inventory figure — appears on the typewriter. The same remote machine may be used to introduce information directly to the memory. The 305 RAMAC may be interrogated in a similar manner directly from the machine’s console.
The monthly charge for 305 RAMAC is $3,200. Prices on the 650 RAMAC will be announced at a later date. Deliveries on both will start in mid-1957 although several test 305 RAMAC’s are being delivered this year.