Beginning in the late 1960s, IBM engineers in Boulder, Colorado began to research and test an inexpensive high-capacity storage system built around the concept of magnetic tape cartridges. Their idea was to have the tapes retrieved by a robotic arm and fed into a unit that could read/write several tapes simultaneously. In 1970, the data storage invention was code-named “Comanche”, categorized as an online tape library with the ability to provide computer-controlled access to stored information. Finally, in October 1974, “Comanche” was introduced as the IBM 3850 Mass Storage System (MSS).
The Mass Storage System or MSS as it was referred to, comprised of a library of tube-shaped plastic cartridges, two inches wide and 4 inches long, each holding a spool of tape 770 inches long. Each spool of tape was able to store up to 50MB with each virtual disk requiring a pair of cartridges. These cartridges were kept in a hexagonal array of bins in the IBM 3851 Mass Storage Facility. New cartridges were then rolled into the MSS and were automatically stored in an empty bin. The data stored on the tape was retrieved via virtual IBM 3330 disk drives and collected on a mix of 3330 and 3350 staging drives. Staging and Destaging became known as the process of data being transferred between a cartridge and disk drive.
The tape cartridges were moved into and out of read/write facilities by two motorized robotic arms. Stage time for data from cartridge to disk was 15 seconds on average, including the two seconds it took to move the cartridge into a read station, and eight to ten seconds it took to read the tape. This method of recording data was extraordinary for its time.
The IBM 3850 MSS offers a new idea in data storage, merging the random-access feature of disk drives with the benefits of tape drives. With the data cartridge as its main piece, the new system features capacities from 35 billion to 472 billion characters of data. The cost-effective storage solution can reduce a user’s cost per million characters to as little as one-tenth the cost of online magnetic disk storage, at the same time. Furthermore, it allows users to achieve new heights of data consumption by expanding the virtual storage model to magnetic disk devices. The storage system’s virtual drives can assist the user in managing more jobs at the same time than with conventional magnetic tape and disk storage drives.