IBM 305 RAMAC

The IBM 305 RAMAC was the first commercial computer that used a moving head hard disk drive (magnetic disk storage) for secondary storage. IBM introduced the storage unit on September 4, 1956 before unveiling the entire computer nine days later on September 13.cite web | url=http://www-03.ibm.com/ibm/history/exhibits/storage/storage_350.html | title=IBM Archives: IBM 350 disk storage unit | accessdate=2007-09-01] [cite web | url=http://www-03.ibm.com/press/us/en/pressrelease/20209.wss | title=IBM Details Next Generation of Storage Innovation | date=2006-09-06 | accessdate=2007-09-01] [cite news | url=http://www.eweek.com/article2/0,1895,2014003,00.asp | title=IBM Builds on 50 Years of Spinning Disk Storage | first=Chris | last=Preimesberger | publisher=eWeek.com | date=2006-09-08 | accessdate=2007-09-01] RAMAC stood for "Random Access Method of Accounting and Control". Its design was motivated by the need for real time accounting in business. [http://www.youtube.com/watch?v=zOD1umMX2s8 IBM RAMAC promotional film] ] The first RAMAC to be used in the US 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. The IBM 350 disk system stored 5 million 8-bit (7-bits plus 1 odd parity bit) characters (about 4.8 megabytes). It had fifty 24-inch diameter 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 [http://www.bls.gov/data/inflation_calculator.htm 1957 dollars] , equivalent to a purchase price of about $160,000. More than 1000 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computer became obsolete in 1962 when the IBM 1405 Disk Storage Unit for the IBM 1401 was introduced, and the 305 was withdrawn in 1969.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') by 15 m (50'); the 350 disk storage unit measured around 1.5 m² (16 sq ft). The first hard disk unit was shipped September 13, 1956 [ [http://www.msnbc.msn.com/id/14096484/site/newsweek/ 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 plug-board.

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, punch card data collection, and a central printing facility.

In an interview [Lee Gomes, "Talking Tech" "The Wall Street Journal", August 22, 2006 ] published in the Wall Street Journal with Currie Munce, research vice president for Hitachi Global Storage Technologies, which acquired IBM's storage business, said the entire RAMAC unit weighed over a ton and had to be moved around with forklifts and delivered via large cargo airplanes. According to Munce, while the storage capacity of the drive could have been increased above five megabytes, the marketing department at IBM was against a larger capacity drive because they didn't know how to sell a product with more storage.

Architecture

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

External links

* [http://www-1.ibm.com/ibm/history/exhibits/storage/storage_PH0305.html IBM Archives on the 305]
* [http://ed-thelen.org/comp-hist/BRL61-ibm03.html#IBM-305-RAMAC IBM 305 RAMAC Data Processing System]

Footnotes