 The IBM 350 drive had fifty platters, with a total capacity of five million 6-bit characters (3.75 megabytes).A single head assembly having two heads was used for access to all the platters, yielding an average access time of just under 1 second.The RAMAC disk drive created a new level in the computer data hierarchy, today known as secondary storage, less expensive and slower than main memory (then typically core or drum) but faster and more expensive than tape drives.