History (2004): HDD Areal Density Reaches 1Tb/Square Inch

This article comes from the Computer History Museum.

2014: HDD areal density reaches 1 terabit/sq. in.
New technologies promise densities up to 10 terabits per square inch

Disk Areal Density Trend 1957–2010

(Courtesy International Business Machines Corporation)

Areal density, the number of bits of information that can be stored on the surface area of a recording medium, is the major factor in determining the maximum capacity of a technology. The term is used to characterize magnetic, optical, and semiconductor storage but is most frequently applied to disk drives, where the number of bits per linear inch (bpi) times the number of tracks per radial inch (tpi) yields the areal density.

The IBM 350 RAMAC disk of 1956 held 100bits/inch with a track density of 20bits/inch for a density of 2,000 bits/square inch.

Developments in manufacturing processes for both drives and media together with electronic, mechanical, and software design improvements increased areal density on the IBM 3330 shipped in 1971 to 780,000 bits/square inch (4,040bpi x 192tpi) for a CAGR of 50% per year.

For the next 20 years, as the underlying technologies matured, the annual rate of increase slowed to around 25%. The introduction of magnetoresistive (MR) read-heads together with film disks and intelligent interfaces revived the CAGR to 60%.

Areal density in commercial drives reached 1Tb/square inch in April 2014 when Seagate announced the model 6TB that employed Shingled Magnetic Recording (SMR) technology in a 3.5-inch form factor.

In 2015 Toshiba Corporation announced that it had also achieved an areal density of 1Tb/square inch in a 2.5-inch HDD by extending conventional PMR technology.

Over the period 1956 to 2014 the average CAGR for HDDs of 41% was identical to the Moore’s Law rate for semiconductor devices.

Research papers and laboratory demonstrations of new head and media technologies, such as heat assisted magnetic recording (HAMR), microwave assisted magnetic recording (MAMR), and bit pattern media (BPM) promise areal densities of up to 10Tb/square inch. These new technologies will require significant change to the HDD hardware and/or the data storage architecture.