CHAPTER 2Where Are We, and How Did We Get Here?

As long as there has been digital data there has been a need to destroy it, if only to make room for fresher data. When data was recorded on punch cards or paper tape, erasure was a simple matter of burning or shredding the medium. One of the most unusual ways to store data in the early days of digital computers was via acoustic storage. A long wire in a metal housing that bore a resemblance to latter-day hard drive cases was coiled on one end and led to a read-write “head” at the other. Writing involved a timed hammer that would strike the wire creating an acoustic impulse that would travel along the wire in its many coils. When this acoustic wave returned from its journey around the coil, a pickup would “read” it and cause the hammer to re-strike the wire in the same time slot as the original. This would create a record of precisely timed acoustic signals traveling around the wire. Erasure was simply a matter of not striking the wire again or cutting power to the storage device.

2.1 Digital Data Storage

Digital data storage is simply a matter of recording ones and zeros in a way that can be read. This could be done with beads on a string, with a bead representing a 1 and a gap representing a 0. A byte could be 8, 16, 32, or 64, beads+gaps. Any recorded ...

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