Editing IBM 305 RAMAC (section)

==Overview==
The first hard disk unit was shipped September 13, 1956.<ref>[http://www.newsweek.com/hard-disk-changed-world-108939 Steven Levy, "The Hard Disk That Changed the World" ''Newsweek'', August 7, 2006]</ref> 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 <!--305 RAMAC Manual of Operation (ref 4) says "In effect, the machine stores the equivalent of 62,500 80-column IBM cards", not sure there is a conflict, maybe other number adds drum memory to it?): --> touted the system as being able to store the equivalent of 64,000 [[punched card]]s.<ref name=film/>

The 305 was one of the last [[vacuum tube]] computers that IBM built. It weighed over a ton.<ref>{{Cite web|url=http://www.ed-thelen.org/comp-hist/BRL61-ibm03.html#IBM-305-RAMAC|title=IBM 305 RAMAC|last=Weik|first=Martin H.|date=March 1961|website=ed-thelen.org|series=A Third Survey of Domestic Electronic Digital Computing Systems|at=See ''SUNOCO Philadelphia''}}</ref>

The [[IBM 350]] disk system stored 5 million [[alphanumeric]] characters recorded as six data bits, one [[parity bit]] and one space bit for eight bits recorded per character.<ref>{{cite web |url=http://www.ed-thelen.org/RAMAC/IBM-227-3534-0-305-RAMAC-r.pdf |title=RAMAC 305 Customer Engineering Manual of Instruction <!-- at least not part of the actual title (right part was substituted): Theory Of Operations--> |work= IBM Corp., 1959 |pages=7–8 and 85}}</ref> It had fifty {{convert|24|in|mm|adj=mid|-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 [[Servomechanism|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 US$3,200 ({{Inflation|US|3200|1957|fmt=eq|r=-2}}) per month.

[[Image:RAMAC 305 disk.JPG|thumb|right|One RAMAC storage disk showing [[head crash]] damage]]
[[File:BRL61-IBM 305 RAMAC.jpeg|thumb|IBM 305 at [[U.S. Army]] Red River Arsenal. Foreground: two 350 disk drives. Background: 380 console and 305 processing unit]]
The original 305 RAMAC computer system could be housed in a room of about 9&nbsp;m (30&nbsp;ft) by 15&nbsp;m (50&nbsp;ft); the 350 disk storage unit measured around {{convert|1.5|m2|sqft|sp=us}}. 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<ref>Lee Gomes, "Talking Tech" ''The Wall Street Journal'', August 22, 2006</ref> 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 did not know how to sell a product with more storage.
[[Image:IBM 350 RAMAC.jpg|thumb|RAMAC mechanism at Computer History Museum]]

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.