Ct2 core reading pdf
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Com is a tool that allows blind and visually impaired users to read any document in Adobe PDF format. The tool converts PDF documents into simple HTML or ASCII text, which can then be read by a number of common screen reading programs that synthesize the HTML as audible speech. Some of the features on CT. A 32 x 32 core memory plane storing 1024 bits of data. Magnetic-core memory was the predominant form of random-access computer memory for 20 years between about 1955 and 1975. Such memory is often just called core memory, or, informally, core.
Each core represents one bit of information. Using smaller cores and wires, the memory density of core slowly increased, and by the late 1960s a density of about 32 kilobits per cubic foot was typical. However, reaching this density required extremely careful manufacture, almost always carried out by hand in spite of repeated major efforts to automate the process. 1 per bit to about 1 cent per bit. The basic concept of using the square hysteresis loop of certain magnetic materials as a storage or switching device was known from the earliest days of computer development. Much of this knowledge had developed due to an understanding of transformers, which allowed amplification and switch-like performance when built using certain materials. Frederick Viehe applied for various patents on the use of transformers for building digital logic circuits in place of relay logic beginning in 1947.
A patent on a fully developed core system was granted in 1947, and later purchased by IBM in 1956. Substantial work in the field was carried out by the Shanghai-born American physicists An Wang and Way-Dong Woo, who created the pulse transfer controlling device in 1949. The MIT Whirlwind computer required a fast memory system for real-time aircraft tracking use. In April 2011, Forrester recalled, “the Wang use of cores did not have any influence on my development of random-access memory. The Wang memory was expensive and complicated. As I recall, which may not be entirely correct, it used two cores per binary bit and was essentially a delay line that moved a bit forward.
To the extent that I may have focused on it, the approach was not suitable for our purposes. He describes the invention and associated events, in 1975. A third developer involved in the early development of core was Jan A. A prolific inventor, Rajchman designed a unique core system using ferrite bands wrapped around thin metal tubes, building his first examples using a converted aspirin press in 1949. Two key inventions led to the development of magnetic core memory in 1951.
The first use of core was in the Whirlwind computer, and Project Whirlwind’s “most famous contribution was the random-access, magnetic core storage feature. It was during the early 1950s that Seeburg developed the use of this coincident current ferrite core memory storage in the “Tormat” memory of its new range of jukeboxes, starting with the V200 released in 1955. Development work was completed in 1953. Numerous uses in computing, telephony and industrial control followed. Wang’s patent was not granted until 1955, and by that time core was already in use. Wang used the funds to greatly expand Wang Laboratories, which he had co-founded with Dr. Ge-Yao Chu, a school mate from China.
13 million for rights to Forrester’s patent—the largest patent settlement to that date. Forrester’s coincident-current system required one of the wires to be run at 45 degrees to the cores, which proved impossible to wire by machine, so that core arrays had to be assembled under microscopes by workers with fine motor control. By the late 1950s industrial plants had been set up in East Asia to build core. Inside, hundreds of workers strung cores for low pay. Core was replaced by integrated semiconductor RAM chips in the 1970s.
Core memory was part of a family of related technologies, now largely forgotten, which exploited the magnetic properties of materials to perform switching and amplification. X and Y are drive lines, S is sense, Z is inhibit. Arrows indicate the direction of current for writing. Y wires are dull brown and vertical, toward the back. The sense wires are diagonal, colored orange, and the inhibit wires are vertical twisted pairs.
The term “core” comes from conventional transformers whose windings surround a magnetic core. In core memory, the wires pass once through any given core—they are single-turn devices. The properties of materials used for memory cores are dramatically different from those used in power transformers. Core relies on the “square loop” properties of the ferrite material used to make the toroids. An electric current in a wire that passes through a core creates a magnetic field. The toroidal shape of a core is preferred since the magnetic path is closed, there are no magnetic poles and thus very little external flux. This allows the cores to be packed closely together without allowing their magnetic fields to interact.
The alternating 45-degree positioning in a core array helps to reduce any stray coupling. Diagram of the hysteresis curve for a magnetic memory core during a read operation. To read a bit of core memory, the circuitry tries to flip the bit to the polarity assigned to the 0 state, by driving the selected X and Y lines that intersect at that core. If the bit was already 0, the physical state of the core is unaffected. If the bit was previously 1, then the core changes magnetic polarity. This change, after a delay, induces a voltage pulse into the Sense line.