UNIVAC Magnetic Tape

This tape is a 1⁄2-inch-wide strip of nickel-plated phosphor bronze (called Vicalloy) and is 1200 feet long. Modern magnetic tape is a very thin coating of iron oxide on Mylar and is much lighter than these reels of metal tape. The nickel-plated phosphor bronze tape was very abrasive so the UNISERVO tape drive had a moving film of plastic buffer tape between the tape and the tape head to prevent wear. The were six tracks for the data, one for parity, and one for timing. The data was recorded at 128 bits per inch resulting in a capacity of about 1.5 MB per tape. The tape drive could move the tape at 100 inches per second resulting in a transfer rate of 12,800 characters per second. The data was recorded in a fixed size block of 60 words of 12 characters each.

The UNISERVO drive supported both reading and writing in both forward and backward directions. DECtape drives offered by Digital Equipment about 10 years later has the same forward/backward capability. Data transfers to/from the UNIVAC I processor were fully buffered in a one block dedicated memory. This allowed the processor to execute instructions at the same time data was being transferred to/from the UNISERVO.

UNIVAC continued to use the name UNISERVO for later models of tape drive (e.g., UNISERVO II, UNISERVO IIIC, UNISERVO VIII-C) for later computers in their product line. The UNISERVO II could read metal tapes from the UNIVAC I as well as use higher density PET film base/ferric oxide media tapes that became the industry standard. While UNIVAC was first with computer tape, and had higher performance than contemporary IBM tape drives, IBM was able to set the data interchange standard. UNIVAC was later forced to be compatible with the IBM technology.

You can watch a video on the UNIVAC computer below. The tape drives are described at 5:35.