Although the size, capacity and internal electronics of hard drives have changed massively, the basic principles remain the same as they were 50 years ago. See our photo gallery for more images.
Hard disk basics
The basic idea behind a hard disk is simple enough. Take a recording medium that can remember the alignment of a magnetic field -- iron oxide, for example -- and move it beneath an electromagnet that's getting pulses of electricity. Those pulses will form a pattern of magnetism in the medium. Move the same medium past a coil of wire, and the magnetic pattern will induce a series of electrical pulses that reprise the originals. The only differences between the RAMAC and the iPod -- and the thousands of hard disk designs between -- are ones of scale and detail.
Hard disks are made of a series of separate platters coated in the recording medium, held apart by spacers on a spindle. Each platter surface has a read-write head attached to an arm or armature. One motor spins the spindles, another moves the head arms; the heads are connected to a preamplifier to turn the tiny electrical pulses into signals that can be decoded, and a driver circuit to make the carefully shaped pulses that write to the disk. As the platters spin, they create an air cushion on which the head rides. More platters, higher spindle speeds and more precise arm controls make for more data at a faster speed.
Hard drive hall of fame
Here's a brief look at some notable hard drives in history
|IBM 350. Consists of 50 disks, each 24 inches in diameter.
|IBM creates a storage system based on packs of six 14-inch disks. Each pack holds 2MB. Commercially, this is when hard drives take off.
|IBM develops an 8-inch drive.
|The 5.25-inch 'Winchester' drive makes its debut. Its design plays a key role in the development of the PC market.
|Rodine releases a 10MB 3.25-inch drive. It's still the standard form factor for desktops.
|PrairieTek releases its 2.5-inch 20MB drive; this size remains the standard for notebooks.
|Integrated Peripherals debuts its 1.8-inch drive. Drives this size aren't destined to go mainstream until the debut of Apple's first iPod, more than 10 years later.
|Hewlett-Packard produces a 1.3-inch drive. It doesn't make a major impact, although drive manufacturers are now thinking about bringing it back.
|IBM releases a 1-inch microdrive with 340MB of capacity. That capacity has since expanded to 8GB.
|Toshiba shrinks the microdrive to 0.85 inches in diameter. Many believe that this is the smallest size of drive that will be mass-produced.
Hard disk evolution
As the hard disk evolved, though, changes in scale brought their own side effects. Early hard disk drives were open to the air and often had exchangeable sets of platters that could be slotted in and out of the drive itself, similar to floppy disks. Because the heads rode a long way above the medium and storage densities were so much less than today -- the RAMAC managed 2Kbits per inch, compared to the Toshiba drive's 178.8Gbits per inch -- the dust particles in normal air didn't disrupt the mechanism. But by 1973, when IBM produced a twin-spindle hard disk with 30MB per spindle, it had to put the head and disk assembly in a dust-free enclosure. That device, the 3340, became known as the Winchester (after the 30-30 Winchester rifle) -- a generic name for small hard disks that, like much IBM terminology, lasted into the PC era.
PCs were the main motive force behind many of the later innovations. In 1980, Seagate Technology -- founded by industry mainspring Al Shugart, who had been involved with the RAMAC at IBM -- launched the ST-506, the first 5.25in. hard disk, which at 5 megabytes had fourteen times the capacity of the floppy disk drives that would fit in the same space. The controller cards for the hard disks frequently had almost as much computing power as the PCs themselves, with the first IBM PC controllers taking up a full-length expansion slot and containing a Z80 processor.
Western Digital, which made some of those first interface cards, was behind one of the major evolutionary steps in PC hard disks. The company moved the controller circuitry onto the drives themselves, calling the technique IDE (Integrated Drive Electronics). This was then adopted as a standard for the IBM PC/AT, the next major development from the original specification, and renamed as the AT Attachment interface or ATA. Over time, this has evolved and been subsumed in other standards, to the point where it can be found in enterprise-level storage systems competing or supplanting earlier, higher-performance disk interface standards such as the Small Computer System Interface (SCSI). The iPod hard disk uses ATA-6, for example.
Another area of rapid development has been the recording medium. The RAMAC used brown paint containing iron oxide; the latest drives use nickel phosphor layered with cobalt zirconium niobium laid down using similar techniques to those found in the making of silicon chips. The magnetic domains no longer line up end to end on the surface of the disk like bar magnets flat on a table; instead, they are stacked end-on like Macdonald's fries. Although this perpendicular recording has only recently been re-adopted, it was first used in the RAMAC itself -- although IBM swiftly dropped it for the next generation.
The hard disk's future looks secure -- for now. It still costs hundreds of times less per bit than flash memory, which has frequently been touted as the hard disk's successor, although a combination of flash memory and hard disk in the same device may become popular as a way to speed up boot times and reduce power consumption in portable computers. Future improvements in disk technology include heat-assisted recording and patterned material. Both of these techniques address the problem of adjacent bits affecting each other because they're so small that virtually no energy is required to flip them from one state to another. Seagate says this will help to push densities up to between fifty and a hundred terabits per square inch, or around five hundred times that of today's iPod disk.
After that, new technologies that combine magnetic recording with solid-state devices are likely to appear, with the state of single atoms set by direct control of electron spin. This is predicted to reach to four petabits per square inch, perhaps even beyond. At that point, the hard disk revolution will have spun its last, making it unlikely that it will equal the CRT's record of a hundred years as a viable component. Between then and now, however, there's a lot more data to be stored on one of the most ubiquitous, useful and underappreciated pillars of the digital age.