History (2005): Perpendicular Magnetic Recording Arrives

This article comes from the Computer History Museum.

2005: Perpendicular Magnetic Recording arrives
PMR raises disk drive areal density above 100 gigabits per square inch

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Comparison LMR vs. PMR

(Hitachi Global Storage Technologies)

Perpendicular magnetic recording (PMR) bits align vertically and offer a significant increase in areal density compared to conventional longitudinal magnetic recording (LMR) technology.

Ampex engineers had evaluated PMR for tape and IBM investigated the technology for the IBM 1301 drive but it did not reach commercial application until 2005.

The combination of PMR media and shielded magnetoresistive (MR) head technology enables multi-terabyte drives with areal densities approaching one trillion bits/square inch.

The bit size supported by a magnetic medium is inversely proportional to its coercivity and coercivity is limited by the magnetic field achievable by the write element of the recording head. The combination of optimized PMR media and head approximately doubles the magnetic write field achievable with LMR. A stronger write field enables the use of higher coercivity media with smaller bit sizes and higher areal density. Disk media with magnetic crystallites oriented perpendicular to the surface and isolated from each other by oxide barriers used in combination with shielded write heads have extended HDD areal density by a factor of 10 since the introduction of PMR.

At Tohoku University, Japan, professor Shun-ichi Iwasaki championed PMR from the middle 1970s. In 1995, following Professor Stan Charap’s prediction that the areal density of longitudinal recording would be limited by superparamagnetism, it was recognized at a National Storage Industry Consortium (NSIC) – sponsored workshop that perpendicular recording could be extended to higher densities.

Toshiba, Seagate and HGST led the commercialization of PMR disk drives between late 2005 and mid-2006. The Toshiba MK4007GAL featured an aerial density of 133Gb/square inch.

All major industry vendors adopted PMR technology and within two years HGST introduced a 1TB drive, the Deskstar 7K1000, with an areal density of 325Gb/square inch.