Those are tape drives, albeit large ones. As the tape passes the head, the data is read or written, as the case may be. Tapes have the advantage of being inexpensive, and rather reliable. But they are slow, because they are sequential access devices. This means you must advance or rewind the tape to the position where the requested data starts, much as you must advance and rewind a cassette tape to locate a song.
Tapes are also slow due to the nature of the media.
While data transfer can be increased by increasing the speed of the tape, this can lead to two problems. One, the heads are more likely to miswrite due to not having enough time to align the polarities of the magnetic particles, or may misread due to the tape not being under the head long enough. If the tape stretches too much, then it will render it unusable for data storage, and data loss may result. The first hard drive came about in 1956. That is about five megabytes.