Inside a modern hard disk

Most of us don’t give our hard drives a second thought; after all, it’s just something on which to store files and photos.

They generally only come to our attention when they start irritating us by making noises or driving us to despair when they fail and lose countless hours of important work.

But have you ever wondered how they work or what’s inside them? In this feature we will explain how these mass-produced yet precision engineered products came about.

A brief history
The hard disk has been around for more than 50 years now.

The grandfather of all hard disks was IBM’s 350 storage unit (or ‘disk file’ as IBM called it), used in the 305 Ramac computer in 1956.

It used 50 24in magnetic disks (platters) to hold five million 7-bit data characters and had one head for reading and writing data.

But it was in 1973 that IBM introduced the technology on which most of today’s drives are based. The 3340 or, to use its more popular name, the Winchester drive, introduced low-mass heads, lubricated disks and a sealed assembly. It had a capacity of 35MB or 70MB via two or four 14in disks.

1980 saw the first 5.25in full-height drive, the Seagate ST-506, which was the first hard drive for personal computers and held 5MB of data. Three years later Rodime introduced the 3.5in half-height form factor that we all know today, with the RO352 which held 10MB of data on two 3.5in platters.

1988 saw the first low-profile 3.5in drive, the Conner Peripherals CP3022, which had a capacity of 21MB on a single 3.5in platter. This form factor became the standard for modern drives. The first 2.5in drive appeared the same year, when a company called Prairie Tek launched the 220, storing 20MB on two 2.5in platters.

The start of the 1990s saw IBM bringing three important advances in the way drives access data. The IBM Redwing, an 857MB drive launched in 1990, was the first to use magneto-resistive (MR) heads and a type of data decoding called PRML (partial response maximum likelihood). A year later IBM’s Pacifica mainframe drive was the first drive to replace the magnetic oxide medium on the platter surface with a thin film medium.

The first 10,000rpm drive arrived in 1997 with Seagate’s launch of the ST19101 Cheetah 9, which used eight 3.5in disks to provide 9.1GB of capacity ­ and a year later they had the first 10,000rpm drive with 3in disks, the Cheetah 18 (ST118202), which used 12 disks for its 18.2GB capacity.

The same year saw Hitachi bringing out an even faster drive, the DK3E1T-91, which had a spin speed of 12,000rpm, and in 1999 IBM launched the 1in Microdrive.

The turn of the century saw Seagate reclaim the fastest spin speed crown with the Cheetah X15, rotating at 15,000rpm with a capacity of 18.3GB.

As well as capacities, drive interfaces improved, with the parallel ATA standard becoming faster, and then in 2003 the Serial ATA Working Group published the serial ATA (Sata) 1.0a specification. It’s become well established, and now the drives in most new systems use the Sata interface.