Magnetic drums refer to two types of equipment: drum memory used in early computers and magnetic drum separators used in recycling. The former stored data on a magnetized metal cylinder, while the latter separates metals from other materials using magnetic fields. Drum memory was the primary working memory in early computers, but was eventually replaced by more modern storage methods. Magnetic drum separators are used in the recycling industry to sort materials by attracting scrap metal with magnetic fields.
Two different types of equipment are referred to as magnetic drums. One type is a data storage device used in early computers, also known as drum memory. The other is a magnetic drum separator, a tool used in the recycling industry to separate metals from other materials.
The magnetic drum used for computer memory was invented in 1932. In the 1950s and 1960s, it was the primary working memory in most computers. Main memory, the forerunner of random access memory (RAM), gradually replaced drum memory as primary storage, although magnetic drums continued to be used as secondary storage for a while.
In the computer industry, a magnetic drum consisted of a hollow metal cylinder covered in a magnetizable material. The read and write heads recorded data on the drum as it rotated by emitting electromagnetic pulses to magnetize small dots to record a binary value of zero or one. The same heads could “read” the recorded data by detecting the magnetized points. A surface of the drum has been divided into tracks and sectors so that users can indicate where information should be stored and avoid overwriting previous data.
Compared to more modern storage methods, magnetic drums could store a very small amount of data. A drum 4 inches (about 10 cm) in diameter and 8 inches (about 20 cm) long could hold about 500 bits. There are eight bits in a byte, the basic unit of digital information, so the drum could hold about 62 bytes. Most computer memory in the early 21st century is measured in gigabytes, a unit of 10^6 bytes. Drum memory was several orders of magnitude smaller than its modern counterparts, but it was the standard memory type for early computers.
In the recycling industry, a magnetic drum separator can be used to help sort materials. Recycled materials are fed through a chute at the top or bottom of the drum. Scrap metal sticks to the drum, while other non-magnetic materials fall off the drum. The drums are designed so that one side is constantly magnetised, while the other is not; when the scrap metal lands on the non-magnetized side, it falls in a different position than the other materials.
Magnetic drum separators consist of a rotating magnetic cylinder capable of capturing the incoming metal. To attract scrap metal they can use electromagnetic circuits; magnetic fields; or rare earth materials, which are a group of magnetic metals. Magnetic drum separators are available in a variety of sizes to accommodate varying volumes of materials.
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