History (1990): Gigabit on Square Inch on HDD Disk Media Surface by IBM

IBM Corp. (San Jose, CA) set a world record in magnetic data storage density storing a billion bits of information on a single square inch of a disk surface using experimental components.

The IBM team says the public can expect significant improvements in the magnetic storage capacity of their computers from laptops to supercomputers, to continue into the next century.

To achieve gigabit storage density, the researchers combine a number of advanced components, including experimental thin-film recording heads and disks and sophisticated electronics.

The demonstration was performed on a precision test apparatus, but all of the critical hardware components were made by conventional manufacturing processes.

Several additional years of development would be required before gigabit technology could incorporate into products.

The gigabit demonstration was performed at IBM’s Almaden Research Center in a collaboration involving the company’s Research and General Product’s divisions. Located in San Jose, CA, the Almaden Research Center is one of IBM’s 4 basic research laboratories managed by the company’s Research Division. The General Products Division develops and manufactures large-capacity magnetic disk and tape drives. The experimental dual-element, thin-film recording head used in gigabit demonstration features an inductive write element and MR read element. Both elements operate while the head flies over the disk at a height of less than 2 millionths of an inch, so narrow a gap that even visible light can’t pass through.

Heads in currently availability disk drives fly from 6 to 15 millionths of an inch above the disk surface.

The MR head used in the gigabit demonstration is similar in principle to the industry’s first MR head, introduced by IBM in 1984 in the 3480 magnetic tape subsystem.

In the present demonstration, however, the recorded tracks are more than 100 times narrower than those in the IBM 3480. This required the development of innovative MR head design and fabrication methods in order to retrieve detectable signals reliably from the ultra-small bit cells during reading.

Composed of several layers of very thin films, the MR head is made by photolithographic methods common in the semiconductor industry. The aluminum disk is coated with a thin film of a magnetic cobalt alloy.

In the gigabit demonstration, bits were stored at a linear density of 158,000bpi along concentric tracks packed at 6,350 per radial inch. Each data bit measures only 0.16μ long by 4μs wide in size, comparable in area to current optical storage bit cells.

The demonstration also relied on an innovative recording channel, known as the Partial Response, Maximum Likehood (PRML) channel, which permits significantly greater bit density. A channel consists of electronics that converts data into a form that can be written accurately onto a disk and during reading, reverse the process.

During the demonstration, information was recorded at a data rate of 3.5 million bytes per second. The measured error correction rates during the gigabit tests were one in a billion, decreasing to one in 10 trillion, if standard ECC are employed.

This article is an abstract of news published on the former paper version of Computer Data Storage Newsletter on issue ≠24, published on January 1990.