Anatomy of a Hard Disk

Contributing Writer, Computerworld |

Almost all computers today store their digital information as magnetic areas on a device called a fixed disk, disc drive operating room fixed disk.

Basically, all hard drives work the same way: Selective information is encoded and "written" onto a round, spinning aluminum or glass platter that's been coated with magnetic material. The writing is cooked by a magnetic head, mounted at the end of an arm that pivots in such a way that the head can be positioned over any start out of the disk. The same head likewise reads the stored data. Special software program or microcode on the harrow drive and the computer continue track of where any piece of information is stored. Older disk drives devoted one entire side of one disk, along with its head, as a servomechanism to calibrate and regulate platter and arm motion, but current technology doesn't necessitate nearly soh much space.

Remember when music came on vinyl records? A disk drive operates a great deal alike the phonograph. Each has a motor that spins a platter containing information that is transcribed or retrieved by a special device mounted on the end of an arm that pivots across the platter.

There are considerable differences, of course. The LP record was plastic and 12 in. in diameter, and it spun at 33-1/3 rpm. The computer hard drive, once 14 in. or more crossways, is straight off no bigger than 3.5 or 5.5 in. in diam, with those in laptops and hand-held devices at 2.5, 1.8 or even 1 in. Problematic disks spin at speeds ranging from about 4,000 to 15,000 rpm, and those speeds are likely to gain in the early. And where the phonograph phonograph needle physically touched the record groove, the effort heads preceptor't touch the spinning media at all, though they get very close while quick on a cushion of air.

Now's disks can fund immense amounts of data: About the smallest 3.5-in. disc drive being made now will store 10GB, and capacities for individual drives rich person reached 100GB. Drive makers have two ways of increasing the capacity of a hard drive. The simplest method is to add up additional platters along with a separate head for each slope of each platter, and this has been through dormy to well-nig 16 platters. The second, more basic, agency is to increase the amount of data that can be stored on a azygos domain of the magnetic material. This has been the subject of considerable research. Today, IBM has drives that store 25.7GB per square column inch, and the company has demonstrated technologies that can quadruple that, to 100GB of data in a single square inch.

The very commencement disk labour was IBM's RAMAC. Introduced in 1956 the RAMAC's 50 24-in. platters held 5MB of data; the price was $50,000. In 1980, a 14-in. minicomputer disk cartridge could halt perhaps 5MB surgery 10MB of information. The original IBM PC in 1981 didn't support a petrified magnetic disk. When DOS Variant 2 came out, the first disk drives appeared for PC-class machines, exploitation 5.25-in. platters that could store 5MB operating room 10MB and eventually much 40MB of information.

By 1990, it was common for PCs to accompany 40MB disk drives. Five years later, the typical new desktop computer had a 1GB operating theatre 2GB hard drive. Nowadays, you arse buy laptop computers with 30GB drives, and 48GB 2.5-in. drives birth now arrive at the market.

And as for toll, in 1992 I bought an 80MB, 5.25-in. private road at a computer flea market for $300; today's market testament deliver a 20GB 3.5-in. hard drive for a bit more than $100 retail; that's 250 times the capacity at one-ordinal the toll. Put some other way, the 1956 magnetic disc drive was priced at $10,000 per megabyte. In 1992, I paid just $3.75 for each megabyte of entrepot; today, my price for that same megabyte is a half-cent.

The combination of low-toned price and high capacity came together in 1990, when IBM assembled a group of these inexpensive drives into the first Foray into systems that offered surety and error recovery to the mix.

Even in now's world of storage-area networks and network-attached entrepot, the primary unit is the individual magnetic disc drive, and that's perfectly exemplified in the presently pop acronym JBOD — just a bunch of disks.
Inside a Magnetic disc Drive

In this exploded view, you can see the major components that move into a typical drive:


A Platter: Stores the data

B DC spindle motor: Spins the platter

C Head: Reads or writes data from or to the phonograph record

D Actuator: Causes the arm to move

E Printed-tour cable: Connects arm and head to electronics

F Arm: Moves across the disk, locating the head

G Chassis: Cast metal base on which other components are mounted

H Protective shroud: Seals the mechanism against junk

J Logic circuits: Handle speak interlingual rendition, data buffering and I/O requests

Disc operating theatre Disc?

For magnetic media used on computers, disk is the preferred spelling. For other round, unexciting objects, including optical memory board media such as CDs—audio or data—and DVDs, the proper spelling is disc. And where, you ask, did the "hard" ejaculate from? It's used in differentiation to floppy disks, whose magnetic medium was quite flexible but could only embody spun at 360 rpm. The rigid platters in early PC hard drives could twist 10 times as fast—at 3,600 rpm—patc today speeds of twice that are common and several makes possess drives that turn at 15,000 rev.

Right of first publication © 2001 IDG Communications, Iraqi National Congress.