In the 24 years since hard drives wre introduced , they have evolved from immense devices containing up to fifty, half meter diameter disks holding a total of only 5 MB to today's drives, measuring only a few centimeters across and storing up to 70 GB. The precursor of the hard drive was the magnetic drum storage. In 1950 Engineering Research Associates of Minneapolis built the first commercial magnetic drum storage unit for the U.S. Navy, the ERA 110. It could store one million bits of data and retrieve a word in 5 thousandths of a second. In 1956 IBM released the first computer disk storage system, the 305 RAMAC (Random Access Method of Accounting and Control). This system could store five MB on its fifty, 24-inch diameter disks. In 1980, Seagate Technology introduced the first hard disk drive for microcomputers. It was a full height (twice as high as most current 5 1/4" drives) 5 1/4" drive, with a stepper motor, and held 5 Mbytes. In 1980 IBM released the first gigabyte capacity hard drive. It was the size of a refrigerator, weighed 550 pounds (about 250 kg), and had a price tag of $40,000. In 2000, IBM triples the capacity of the world's smallest hard disk drive. This drive holds one gigabyte on a disk which is the size of a R2 coin.
The original IBM PC, introduced in 1981, did not support any type of hard drive. Program code in the BIOS did not recognize any such device and early versions of DOS precluded mass storage by limiting the maximum number of directory entries. After DOS 2 introduced the sub-directory system and support for mass storage devices, companies started selling hard drives for the PC. In 1983, the IBM XT (eXTended) was unveiled with its built-in 10 MB fixed disk. IBM worked with a company to take the controller components normally located in the external cabinet and build them right onto a bus interface card, creating the hard disk controller. In 1984, the IBM AT (Advanced Technology) brought a complete overhaul to hard disk systems. The original AT supported 14 different drive types, recognizing specific hard disks ranging from 10 to 112 MB. DOS versions prior to 4.0 (or 3.31) did not support partitions larger than 32 MB because of sector numbering that could not exceed 16 bit values (up to 65,536 sectors). Many people opted to divide their drives into 32 MB partitions creating a C: D: E: etc. up to the physical capacity.
A modern hard disk drive consists of a motor, spindle, platters, read/write heads, actuator, frame, air filter, and electronics. The frame mounts the mechanical parts of the drive and is sealed with a cover. The sealed part of the drive is known as the Hard Disk Assembly or HDA. The drive electronics usually consists of one or more printed circuit boards mounted on the bottom of the HDA. A head and platter can be visualized as being similar to a record and playback head on an old phonograph, except that the data structure of a hard disk is arranged into concentric circles instead of in a spiral as it on a phonograph record. A hard disk has one or more platters and each platter usually has a head on each of its sides. The platters in modern drives are made from glass or ceramic to avoid the unfavorable thermal characteristics of the aluminum platters found in older drives. A layer of magnetic material is deposited/sputtered on the surface of the platters and most have shiny, chrome-like surfaces. The platters are mounted on the spindle which is turned by the drive motor. Most current IDE hard disk drives spin at 5,400, 7,200, or 10,000 RPM and 15,000 RPM drives are emerging.
The heads (or Winchester sliders) are spring-loaded airfoils and actually fly above the surface of the platters at a distance measured in micrometers. The air stream though which a head "flies" is caused by the spinning of the platters through the air. The heads are extremely small electromagnets. Information is stored on the platters by sending pulses of current from the drive electronics to the head. The direction of the current and thus the direction of the diverging magnetic field across the gap in the head determines the direction the magnetic domains (tiny molecular magnets) on a particular spot on the platter's magnetic coating, and, thus, whether the spot represents a binary one or zero.
Initially hard disks were interfaced to a PC motherboard via an expansion board known as a hard disk controller. The drive performed most of the mechanical functions as well as basic electronic/servo functions; the controller told it in detail what to do.
The development of the IDE drive moved most of the electronics and firmware (low-level software on a chip) from the controller to the drive itself. In the IDE's, a buffer/cache' memory was added to the electronics to speed-up the process of reading and writing hard disk drive data. Overall costs went down and performance went up. A much simpler board, commonly known as an IDE Controller, interfaced the IDE hard disk to the motherboard bus. Subsequently, the IDE Controller expansion board electronics and the connector for the drive cable were incorporated into most motherboards. Most of these motherboards have two IDE interfaces--a Several standards have subsequently been developed to improve upon the IDE drive and incorporate other devices, such as CD-ROMs which can operate off the IDE interfaces.
