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Communications of the ACM


The Life of a Data Byte

binary code on colorful background

Credit: Alesanko Rodriguez

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A byte of data has been stored in a number of different ways through the years as newer, better, and faster storage media are introduced. A byte is a unit of digital information that most commonly refers to eight bits. A bit is a unit of information that can be expressed as 0 or 1, representing a logical state. Let's take a brief walk down memory lane to learn about the origins of bits and bytes.

Going back in time to Babbage's Analytical Engine, you can see that a bit was stored as the position of a mechanical gear or lever. In the case of paper cards, a bit was stored as the presence or absence of a hole in the card at a specific place. For magnetic storage devices, such as tapes and disks, a bit is represented by the polarity of a certain area of the magnetic film. In modern DRAM (dynamic random-access memory), a bit is often represented as two levels of electrical charge stored in a capacitor, a device that stores electrical energy in an electric field. (In the early 1960s, the paper cards used to input programs for IBM mainframes were known as Hollerith cards, named after their inventor Herman Hollerith from the Tabulating Machines Company—which through numerous mergers is what is now known as IBM.)


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