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The IBM 305 RAMAC was the first commercial computer that used a moving-head hard disk drive (magnetic disk storage) for secondary storage. The system was publicly announced on September 14, 1958,〔(650 RAMAC announcement ) The 305 RAMAC and the 650 RAMAC were internally announced on September 4, 1956.〕〔(I. B. M. TO PUT OUT NEW 'THINK' UNITS ), ''New York Times'', September 14, 1956〕 with test units already installed at the U.S. Navy and at private corporations.〔 RAMAC stood for "Random Access Method of Accounting and Control",〔 as its design was motivated by the need for real-time accounting in business.〔(IBM RAMAC promotional film )〕 The first RAMAC to be used in the U.S. auto industry was installed at Chrysler's MOPAR Division in 1957. It replaced a huge tub file which was part of MOPAR's parts inventory control and order processing system. The 305 was one of the last vacuum tube computers that IBM built. It weighed over a ton. The IBM 350 disk system stored 5 million alphanumeric characters recorded as 6 data bits, 1 parity bit and one space bit for 8 bits recorded per character.〔(RAMAC 305 Customer Engineering Theory Of Operations, IBM Corp, © 1959, p.7-8 and 85 )〕 It had fifty disks. Two independent access arms moved up and down to select a disk, and in and out to select a recording track, all under servo control. Average time to locate a single record was 600 milliseconds. Several improved models were added in the 1950s. The IBM RAMAC 305 system with 350 disk storage leased for $3,200 per month in (1957 dollars ), equivalent to a purchase price of about $160,000. More than 1,000 systems were built. Production ended in 1961; the RAMAC computer became obsolete in 1962 when the IBM 1405 Disk Storage Unit for the IBM 1401 was introduced, and the 305 was withdrawn in 1969. The original 305 RAMAC computer system could be housed in a room of about 9 m (30 ft) by 15 m (50 ft); the 350 disk storage unit measured around . The first hard disk unit was shipped September 13, 1956.〔(Steven Levy, "The Hard Disk That Changed the World" ''Newsweek'', August 7, 2006 )〕 The additional components of the computer were a card punch, a central processing unit, a power supply unit, an operator's console/card reader unit, and a printer. There was also a manual inquiry station that allowed direct access to stored records. IBM touted the system as being able to store the equivalent of 64,000 punched cards.〔 Programming the 305 involved not only writing machine language instructions to be stored on the drum memory, but also almost every unit in the system (including the computer itself) could be programmed by inserting wire jumpers into a plugboard control panel. During the 1960 Olympic Winter Games in Squaw Valley (USA), IBM provided the first electronic data processing systems for the Games. The system featured an IBM RAMAC 305 computer, punched card data collection, and a central printing facility. Currie Munce, research vice president for Hitachi Global Storage Technologies (which has acquired IBM's hard disk drive business), stated in a ''Wall Street Journal'' interview〔Lee Gomes, "Talking Tech" ''The Wall Street Journal'', August 22, 2006〕 that the RAMAC unit weighed over a ton, had to be moved around with forklifts, and was delivered via large cargo airplanes. According to Munce, the storage capacity of the drive could have been increased beyond five megabytes, but IBM's marketing department at that time was against a larger capacity drive, because they didn't know how to sell a product with more storage. == Architecture == System architecture was documented in the ''305 RAMAC Manual of Operation''.〔(305 RAMAC Manual of Operation ), IBM, April 1957.〕 The 305 was a character-oriented variable "word" length decimal (BCD) computer with a drum memory rotating at 6000 RPM that held 3200 alphanumeric characters. A core memory buffer of 100 characters was used for temporary storage during data transfers. Each character was 7 bits, composed of two zone bits ("X" and "O"), four BCD bits for the value of the digit, and an odd parity bit ("R") in the following format: X O 8 4 2 1 R Instructions could only be stored on 20 tracks of the drum memory and were fixed length (10 characters), in the following format: :T1 A1 B1 T2 A2 B2 M N P Q Fixed-point data "words" could be any size from one decimal digit up to 100 decimal digits, with the X bit of the least significant digit storing the sign (signed magnitude). Data records could be any size from one character up to 100 characters. 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「IBM 305 RAMAC」の詳細全文を読む スポンサード リンク
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