In 1951 the first magnetic tape media for storing computer data was introduced, using the half inch tape media, used in the UNISERVO tape drive used on the UNIVAC I computer. IBM introduced the 7 track recording format the following year with half inch media wound onto open reel spools, which used the linear recording format.
Half inch open reel media was the standard backup and near line storage medium of choice within the enterprise computer industry. Half inch open reel tape drives have featured in many movies over the years, in some cases long after being obsolete. Half inch open reels are rarely used, although many half inch tape reels are held in storage, containing archived data, which may require data conversion or data recovery when the stored data is required.
History of Half Inch Open Reel Tapes
IBM’s 7 track recording format stored 6 bit values plus a parity bit, adequate for storing textual data until the early 60’s when a replacement was required. The IBM System/360 was introduced in 1964 a 9 track format, which could store 8 bit values in parallel with the calculated parity bit.
Many advances were made during the next three decades such as increasing tape speed and the recording density. These techniques included the use of phase encoding (PE), group code recording (GCR) and non-return-to-zero, inverted (NRZI). Originally a zero bit was indicated by a zero voltage being returned sometimes causing issues with detecting recorded data bits. NRZI introduced the idea of returning a negative voltage making it easier to detect each recorded data bit. Although these advances had enabled more data to be stored with an increased reliability, by the 90s newer tape media using smaller self-contained cartridges were capable of storing much larger quantities of data, leading to the decline of the half inch open reel tape.
Issues with Half Inch Open Reels
Until auto loading tape drives were introduced, loading a half inch open reel could be a complicated process. The tape media is threaded around several guide wheels and across the read/write head, which has proved robust, with few tapes ever suffering an alignment issues or being damaged by the drive mechanism.
The deterioration of the lubrication layer deposited on the surface of the media, is the source of the biggest problems that are seen with half inch open tape media. The lubrication layer will be sticky when it deteriorates which can cause it to stick to the read/write head. All half inch open reel drives feature a safety cut-off which will stop the tape when the tension becomes too high, ensuring no further damage can result. The read/write head will usually become clogged and dirty, with damage resulting to the part of the tape which stuck to it. Even if the media does not stick, if the lubrication layer starts to clog the read/write head it can cause read errors to occur.
Data Recovery and Conversion from Half Inch Open Reels
Many examples of half inch open reel tapes which are seen, even if stored correctly are now suffering the deterioration of the lubrication layer. This means that most half inch open reel tapes will require data recovery. Depending on the state of the media the recovery process can be extremely complex. When the media is in poor condition it will usually require manual intervention by the data recovery engineer to ensure the media streams smoothly.
A well-known but last resort method for treating the lubrication breakdown issue is to back the tape media. Once this process has been undertaken there is only one chance to successfully read the data from the media, as the magnetic recording is destroyed. This process is therefore rarely done until all other non-destructive data recovery techniques have been explored.