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Mellon optical memory was an early form of computer memory invented at the Mellon Institute (today part of Carnegie Mellon University) in the 1950s. The device used a combination of photoemissive and phosphorescent materials to produce a "light loop" between two surfaces. The presence or lack of light, detected by a photocell, represented a one or zero. Although promising, the system was rendered obsolete with the introduction of core memory in the early 1950s. It appears that the system was never used in production, but it represents one of the typically odd earlier attempts to produce a useful high-speed memory system. ==Description== The main memory element of the Mellon device consisted of a vacuum tube consisting of two slightly separated flat glass plates. The inner side of one of the plates was coated with a photoemissive material that released electrons when struck by light. The inside of the other plate was coated with a phosphorescent material, that would release light when struck by electrons. To set up operation, the tube was charged with a high electrical voltage. If an external source of light struck the photoemissive layer, it would release a shower of electrons, amplified by the potential. The electrons would be pulled toward the positive charge on the phosphorescent layer, traveling though the vacuum. When they struck the phosphorescent layer, it would release a shower of photons (light). Some of these photons would travel back to the photoemissive layer, where they would cause a second shower of electrons to be released. To ensure that the light did not activate nearby areas of the photoemissive material, a baffle was used inside the tube, dividing the device up into "cells". The process of electron emission causing photoemission causing electron emission is what provided the memory action. This process would continue for a short time; the light emitted by the phosphorescent layer was much smaller than the amount of energy absorbed by it from the electrons, so the total amount of light in the cell faded away at a rate determined by the characteristics of the phosphorescent material. Overall the system was similar to the better-known Williams tube. The Williams tube used the phosphorescent front of a single CRT to create small spots of static electricity on a plate arranged in front of the tube. However, the stability of these dots proved difficult to maintain. The Mellon system replaced the static charges with light, which was much more resistant to external influence. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mellon optical memory」の詳細全文を読む スポンサード リンク
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