Sunday, December 9, 2007

Part 1: Introduction to hard disk technology - Historical Perspectives

First Hard Disk Image, the RAMDAC
Hard disk drives revolutionized the world. They are used in a myriad of electronic devices from computers to cell phones. The first hard disk was invented at IBM's research lab in San Jose, CA. It held 50 24" platters with a single set of movable heads. Its maximum capacity was 5 MB, a ridiculously small amount by today's standards. It was released in 1956 as the RAMAC (which stands for Random Access Method of Accounting and Control) and sold with one of their early computers, the system 305.

It wasn't until several years later and many technical innovations that the more familiar looking hermetically sealed hard drive was developed. It combined different technologies from several leading companies including: IBM, Shugart Ass., Telex, Tandon, Memorex and finally, Seagate Technologies. Seagate was founded by Alan Shugart and Fenis Connor. The first drives came in 5 MB, 8 MB and 10 MB sizes. I owned several of these early drives in the beginning of my computer consulting days. They contained a 5 1/4 " platter in a form factor about the size of the modern CD/DVD drives in your computer but as much as double the height. It wasn't long after that the smaller 3.5" disk drives were released. Hard Disk Drive capacity increased at an unbelievable pace. The smallest drive commercially available utilizes a 1" platter and is used in cameras and cellphones.

The early drives used a "stepper" motor with a steel band to move the heads. Track positioning was a simple count of the number of steps the motor made. Eventually, the stepper motor was replaced by the "voice coil" motorized head armature. Voice coil motors come from loudspeakers. It consists of a coil of wire used to create a magnetic field on demand and a strong magnetic. When electricity is applied to the coil it causes the coil to repel or attract the coil from the magnet. Voice coils were cheaper to manufacture and easier to control with less moving parts. While greatly improved, this same technology is still in use today.

A discussion of changes in disk technology, disk controller technology and their effects on performance and capacity will be in a follow up post.

Peter Dinhofer


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