IBM 305 RAMAC and the IBM 350 Disk Storage Unit hits 50


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Disk Storage Unit – 50 years on
By Phil Haylor , September 2006 Author of Computer Storage: a Manager’s Guide
The IBM 305 RAMAC computer system launched the disk drive revolution

	The year is 1956 - mechanical memory, CRT tubes and capacitive drums are now devices of a bygone era, whilst punched card, paper tape, magnetic drum stores and magnetic tape are a familiar sight within the landscape of computing. What more could you want? What more could technology possibly offer in terms of data storage? Until the turn of the 1950’s, it was impossible to imagine what might be missing from the world of computing. Then, in 1952, IBM embarked upon a new research & development programme to investigate the concept of a rotating magnetic disk stack, based on its volumetric efficiency for recording surface storage. This research was to provide the answer to the problem of instant ‘filing and finding’ of information and would revolutionise the computer industry. During the 1950’s, paper tape systems had an optimum read speed of about 15 cps (characters per second), whilst drum stores were notorious for malfunctioning and expensive to maintain. Furthermore, magnetic tape continued to be a luxury that only national defence programmes could afford.
IBM 350 disk drive Image: IBM Archives

On this basis, IBM set about researching a new I/O device that was economical to build and maintain, had a scalable volumetric capacity, and would have a relatively fast random access storage capability. This research was based at 99 Notre Dame, San Jose, CA, USA, which was to become the birthplace of magnetic disk storage. On the 4th of September 1956, IBM subsequently launched the 350 Disk Storage Unit, which was taken to market by the IBM 305 RAMAC (Random Access Method of Accounting and Control) computer system. IBM would officially announce the 305 RAMAC computing system to the media on 13th September 1956.

Reynold (Rey) Johnson (1906–1998)
350 Disk Drive Inventor and Senior Project Engineer

The introduction of the 350 Disk Storage Unit increased the utility of the IBM 305 RAMAC, as the 350 made it possible for the first time to file, retrieve and manipulate information from database records in ‘real-time’. As such, the 350 Disk Storage Unit became poised to replace punched card as the primary unit record.

With the cabinet covers on, the IBM 350 Disk Storage Unit measured 5’ 8” tall, 5’ wide and 2’ 5” deep, whilst it weighed in at massive 250kgs. The unit comprised fifty 24” platters, one pair of read/write heads and a pulley system that provided both the vertical and horizontal head movement. Furthermore, the native storage capacity of the disk drive was 5MB (referred to at the time as 5 million characters).

In terms of the platter stack, the media that was adhered to the disk surfaces was just as primitive as the pulley system used to drive the read/write heads. Quite simply, the media consisted of paint that had been refined by squeezing it through women’s stockings, which subsequently had iron filings mixed into it.

Initially it proved very challenging to adhere the magnetic paint to the surfaces of the highly-polished disks. Brushing, spraying and dipping techniques were tried, but left areas of bubbling and pitting in the dried surface.

Eventually, it was found that the magnetic paint could be poured onto a spinning surface using a device that was similar to a potter’s wheel. As the paint was poured onto the surface of the spinning disk. Forces that were exhibited by the spinning motion of the disk would serve to spread the mixture both outwards and fairly evenly across the surface. This motion meant that the disk was effectively ‘painting itself’.

	The read/write head (pictured right) was constructed as a narrow pole tip element, with a 2 mil tip radius and a 2 mil gap.
	Although the maximum density did not error or otherwise ‘roll off’ until 150 bpi was reached, 100 bpi was implemented in the system. With regard to the encoding technique, ‘self-clocking amplitude’ detection was used.
Once in production, 100's of disks were manufactured and tested with the aid of oscilloscopes


	Foreground, two IBM 350 Disk Storage Units in operation

A close up look at some of the specifications of the IBM 350 Disk drive

		Specifications of IBM 350 disk drive
		Platters	Fifty aluminium disks^*1
		Platter diameter	24 inch
		Disk thickness	0.1 inch
		Spacing	0.3
		Height of disk stack	20 inches
		Axis	Vertical
		RPM	1,200
		Media	Iron oxide paint
		Storage capacity	5 million characters
		Data transfer rate	8,800 cps
		Concentric tracks	100 on each side
		Bits per inch	100
		Tracks per inch	20
		Characters per track	500
		Density	100 b/p inch (inside track)
			55 b/p inch (outside track)
		Average seek time	600 milliseconds
		Head type	Inductive (includes an erase gap)
		Head lift method	Air jet
Single arm head positioning option	Dual arm head positioning option	Head-to-disk spacing	800 micro inches (25 mm)
		Air pressure	50 lbs p/inch²
		Head access mechanisms	Up to 3 (in practice) ^*2
The 350 Disk Storage Unit was also available in a storage capacity of 10 million character capacities^*3		Annual rent	$38,000 (approx.)

*1	Up to 120 disks had been added to the axis (in a horizontal position) during early testing
*2	An optional enhancement added in 1958 In addition, 1958 saw the enhancement of the 305 RAMAC computer system, enabling it to connect two 350 Disk Storage Units. This increased the utility of the 305 RAMAC system, providing system storage configurations of 5, 10, 15 or 20 million character storage
*3	Storage capacity was measured using the unit of ‘million characters’, as the 8-bit byte would not come into effect until the introduction of the IBM 360 computer system The character length of the 350 was 6-bit, plus 1 ‘space’ bit
NB:	The 5 million character 350 Disk Storage Unit had a storage capacity equivalent to 940 punched cards
	More than 1,000 IBM 305 RAMAC computer systems were built before production ended in 1961
	Sales figures of the 350 Disk Storage Unit are not currently known
	Model	Announced	Withdrawn
	350 model 1	September 4th 1956	August 18th 1969
	350 model 2	May 5th 1958	August 18th 1969
	350 model 3 & 4	September 15th 1958	August 18th 1969
	350 model 11, 12, 13 & 14	January 12th 1959	August 18th 1969

The potential of the IBM 350 disk drive was quickly recognized by many computing companies, who set about developing their own disk drives. This development was also embraced by producers of Drum Store peripherals as a means to extend their product offerings. Interestingly, non-computing engineering companies also began to diversify and apply their precision engineering skills to this new hi-tech area. By the early 1970’s, the number of companies involved with the disk drive industry had peaked to over 230. However, with the disk drive industry’s appetite for mergers and acquisitions, this figure has declined significantly, whereby only a handful of companies remain today.

Interestingly, such a reduction in the number of disk drive companies has had no detriment to the disk drive industry itself. In fact, disk shipment volumes continue to grow, with some analysts predicting that volume sales over the next 5 years will equal that of the past 50 years. This prediction is further echoed by some futurologists, who suggest that the number of hard disk based products per household will average at around 8 ~ 10 by about 2010. Such a trend would follow one that has been enjoyed by the Compact Disc market, whereby the average household has around 9 ~ 11 CD-type devices, ranging from Hi-Fi’s, personal CD players, in-car music systems, game stations, CD-ROMs and DVD players.

References:
	IBM Archives, (http://www-03.ibm.com/ibm/history/exhibits/storage/storage_350.html {visited August 29, 2006])
	IBM Journal, January 1957, pages 72-75
	Magnetic Disk Heritage Center, (http://www.magneticdiskheritagecenter.org/ [visited August 29, 2006])
	For more information about Phil Haylor, please visit www.intelligentmind.co.uk
	For further information about the Museum of Computing, please visit www.museum-of-computing.org.uk

On this basis, IBM set about researching a new I/O device that was economical to build and maintain, had a scalable volumetric capacity, and would have a relatively fast random access storage capability. This research was based at 99 Notre Dame, San Jose, CA, USA, which was to become the birthplace of magnetic disk storage. On the 4th of September 1956, IBM subsequently launched the 350 Disk Storage Unit, which was taken to market by the IBM 305 RAMAC (Random Access Method of Accounting and Control) computer system. IBM would officially announce the 305 RAMAC computing system to the media on 13th September 1956.
	Reynold (Rey) Johnson (1906–1998) 350 Disk Drive Inventor and Senior Project Engineer






The introduction of the 350 Disk Storage Unit increased the utility of the IBM 305 RAMAC, as the 350 made it possible for the first time to file, retrieve and manipulate information from database records in ‘real-time’. As such, the 350 Disk Storage Unit became poised to replace punched card as the primary unit record. With the cabinet covers on, the IBM 350 Disk Storage Unit measured 5’ 8” tall, 5’ wide and 2’ 5” deep, whilst it weighed in at massive 250kgs. The unit comprised fifty 24” platters, one pair of read/write heads and a pulley system that provided both the vertical and horizontal head movement. Furthermore, the native storage capacity of the disk drive was 5MB (referred to at the time as 5 million characters).