First Computer Tape Drive Originated From Remington Rand

IBM just celebrated the 60th anniversary of its first computer tape drive, the model 726 Magnetic Tape Reader/Recorder, launched May 21, 1952. But historically there was another unit revealed one year before, the UNISERVO from Remington Rand, Inc.’s Eckert-Mauchly Division to be considered as the first tape drive for a computer, the UNIVAC I.

        
                UNISERVO
  You can see the entire tape path
and the two electronic servos arms.

Remington Rand tested UNIVAC on March 30, 1951 and announced its sale to the Census Bureau June 14, 1951, the first commercial computer to feature a magnetic tape storage system, with eight UNISERVO tape drives that stood separate from the CPU and control console on the other side of a garage-size room.

Designed by J. Presper Eckert and John Mauchly, this UNIVERSO, an I/O device for UNIVAC I computer to replace punched card devices, was using linear recording on a metallic tape reel 1,200 feet long and an areal density of 128 characters per inch holding 1.44 million characters or 224KB, the equivalent about 20,000 punched cards.

Data were recorded on eight tracks with six for the data, one for error checking and one for timing channel, and in fixed blocks of 60 words of 12 characters each. The speed of 100 inches per second authorizes a nominal transfer rate of 12,800 characters per second, but an effective one of approximately 7,200 characters per second considering the empty space between the 2,000 blocks that can be recorded on the reel. Each of these blocks, containing 720 characters, were 6 inch long on the reel with space between them of 2.5 inches to provide time for the motor to get up to speed. Each block required the tape to be started and stopped for reading and writing, the information being stored in a buffer.

Writing a block could only be done in the forward direction. When writing, there was an erase head located before the R/W head to clear out the entire width of the tape so that any previous tape could be re-written. Phase encoding (Manchester) was used to record data.

This UNISERVO supported forward and backward modes on read or write operation. Tape motion was controlled by a single capstan connected to a synchronous motor with a high-speed rewind capability.

If a read error was detected, a supervisory panel switch could enable automatic hardware controlled re-reads for five retries. Defects in the reel could be marked by punching a hole through the tape with a hand punch. This was optically sensed and caused a skip forward in the tape motion over the defect.

Inside the unit there was two powerful motors to handle the 5-pound tape, a third one called a Capstan motor for actual reading and writing operations and a fourth one to advance a small mylar tape reel slowly between the metallic tape and the metal R/W head to protect it from wearing out.

"When a tape reel was latched to the left drive it was fastened to the UNISERVO leader with a connector on it that was shaped like a small square "U" with two prongs facing each other. This leader was already threaded through the tape path to a fixed tape reel on the right drive as a result of rewinding. The connection to the tape was made by stretching the two prongs apart and inserting them into a small cylinder at the beginning of the tape. Fastening the tape to the leader was somewhat of a challenge and it was best to let an operator do this. Programmers occasionally injured themselves by getting the prongs caught on a fingernail or on a hand, which could lead to painful bleeding," according to the web page of Allan Reiter. "The tension on the tape at rest was held by two electronic servos that sensed the positions of the two tape loops in the tape path. When the first block was read or written the tape leader moved into position beyond the R/W Head. This would take about 1.5 seconds."

One year later, Big Blue introduced its first tape drive, the second one in the world, the IBM 726, once more to replace punched cards and whose principal inventor was Byron Phelps.

 
     IBM 726 Tape Drive

Recording at 100 characters per second, this 500 feet long 8-inch diameter reel stored the equivalent to 12,500 cards. The unit contained a new vacuum column and magnetic clutch tape drive system and were among the first to use plastic rather than magnetic tape. The seven parallel track tape recorded 6 bits bytes plus one for parity. The density was 100 bits per linear inch and transfer rate 6.1KB/s. The capacity was approximately 2.3MB.

Four years later IBM announced the first HDD, the Ramac 350, for primary storage, tapes then being used as backup media only.