Hard-drive platter for a CDC 6600 computer. The CDC 6600 was the “mainframe” at CRNL in the early 1970s and was the first in a series of “supercomputers”. Stacks of these hard drives, each ~66 cm (26 inch) in diameter and weighing 3.3 kg, were used with the CDC 6600 computer. The discs were made of 3 mm thick aluminum and had a magnetic-recording film on both the top and bottom surfaces. A retiree who worked on the CDC 6600 remembers the storage memory operation as follows:
“The disc platters were mounted on two spindles. Each spindle had two groups of 16 platters and, during operation, would be rotating at 1800 rpm. The read/write heads floated between the platters, such that one read/write head was able to read the surface above it, and below it. Each group of 16 platters thus had 30 surfaces that could be recorded on, leading to a total of 60 recording surfaces. The total capacity of the device (all 60 surfaces) was 131 million, 6 bit characters. Only two inches of that 26-inch surface was recorded on; the transfer rate was not exceeded by any disc manufacturer until the late 1970s.”
A modern DVD, rated at a capacity of 4.7 GB, is also shown for contrast in the first photo. The second photo shows details of the mounting hub. This had to be an extremely stable and balanced device to maintain the positions of the platters precisely at the high rotation speeds used.
