The hard disk drive (HDD) is the workhorse of modern storage systems, from personal computers to enterprise networks. To record data, HDDs change the polarity of tiny sections (magnetic domains) of a magnetic platter. Flipped one way, a domain represents the binary 0; flipped the opposite way, it represents a 1. Domains are arranged in a circumferential fashion around the platters so that a read/write head driven by a servomechanical actuator can track the binary bits . This sort of storage was nothing less than a modern marvel when IBM first introduced the 350 Disk Storage Unit in 1956.
"The 350 Disk Storage Unit consisted of the magnetic disk memory unit with its access mechanism, the electronic and pneumatic controls for the access mechanism, and a small air compressor. Assembled with covers, the 350 was 60 inches long, 68 inches high, and 29 inches deep. It was configured with 50 magnetic disks containing 50,000 sectors, each of which held 100 alphanumeric characters, for a total capacity of 5 million characters."
"Disks rotated at 1,200rpm, tracks (20 to the inch) were recorded at up to 100 bits per inch, and typical head-to-disk spacing was 800 microinches. The execution of a 'seek' instruction positioned a read-write head to the track that contained the desired sector and selected the sector for a later read or write operation. Seek time averaged about 600 milliseconds." 
The 350 was one of six components in IBM's 305 Random Access Memory Accounting (RAMAC) system, which also included an IBM 305 Processing Unit, an 80-position serial-output printer called the 370, a card punch, a console, and a huge power supply. Two years after it was introduced, IBM began offering the 305 RAMAC with an optional second 350 Disk Storage Unit, which doubled capacity. The 305 RAMAC originally leased for $3,200 .
As an interesting aside, each of the RAMAC's 50 aluminum platters was coated with magnetic iron oxide, derived from the same chemical formula as the primer paint used on the Golden Gate Bridge. 
In 1973, IBM introduced the 3340 or Winchester Direct Access Storage Facility. Certainly IBM had not been inactive. The company developed several models between the 305 and the 3340, but the smaller and lighter 3340 marked the next real evolutionary step in hard disk storage.
"The 3340 featured a smaller, lighter read/write head that could ride closer to the disk surface—on an air film 18-millionths of an inch thick, and with a load of less than 20 grams. The Winchester disk file's low-cost head slider structure made it feasible to use two heads per surface, cutting the stroke length in half. The disks, the disk spindle and bearings, the carriage, and the head-arm assemblies were incorporated into a removable, sealed cartridge called the IBM 3348 Data Module. A track density of 300 tracks per inch and an access time of 25 milliseconds were achieved." 
At each step along this evolutionary cycle, storage enabled new applications and greatly increased productivity. Over the next several years, as storage memory continued to evolve, the HDD would emerge as the next new, more adaptable solution and would replace many of the earlier, groundbreaking storage technologies.
 Zeytinci, page 6.
 "IBM 350 Disk Storage Unit," IBM, Armonk, N.Y. downloaded from http://www-03.ibm.com/ibm/history/exhibits/storage/storage_350.html on October 11, 2008.
 "650 RAMAC Announcement," IBM, Armonk, N.Y. (September 14, 1956) downloaded from http://www-03.ibm.com/ibm/history/exhibits/650/650_pr2.html on October 11, 2008.
 Zeytinci, page 7.
 "IBM 3340 Direct Access Storage Facility," IBM, Armonk, N.Y. downloaded from http://www-03.ibm.com/ibm/history/exhibits/storage/storage_3340.html on October 28, 2008.
About Our Blogger
Dean Klein is Vice President of Memory System Development at Micron Technology. Mr. Klein joined Micron in January 1999, after having held several leadership positions at Micron Electronics, Inc., including Executive Vice President of Product Development and Chief Technical Officer. He also co-founded and served as President of PC Tech, Inc., previously a wholly-owned subsidiary of Micron Electronics, Inc., from its inception in 1984. Mr. Klein’s current responsibilities as Vice President of Memory System Development focus on developing memory technologies and capabilities.
Mr. Klein earned a Bachelor of Science degree in electrical engineering and a Master of Electrical Engineering from the University of Minnesota, and he holds over 220 patents in the areas of computer architecture and electrical engineering. He has a passion for math and science education and is a mentor to the FIRST Robotics team (www.FIRSTInspires.org) in the Meridian, Idaho school district.