INTRODUCTION TO HARD DISK DRIVES
A Brief History of the Hard Disk Drive
The hard disk drive has short and fascinating history. In 24 years it evolved from a monstrosity with fifty two-foot diameter disks holding five MBytes (5,000,000 bytes) of data to today's drives measuring 3 /12 inches wide and an inch high (and smaller) holding 400 GBytes (400,000,000,000 bytes/characters). Here, then, is the short history of this marvelous device.
Before the disk drive there were drums... 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 invented the first computer disk storage system, the 305 RAMAC (Random Access Method of Accounting and Control). This system could store five MBytes. It had fifty, 24-inch diameter disks!
By 1961 IBM had invented the first disk drive with air bearing heads and in 1963 they introduced the removable disk pack drive.
In 1970 the eight inch floppy disk drive was introduced by IBM. My first floppy drives were made by Shugart who was one of the "dirty dozen" who left IBM to start their own companies. In 1981 two Shugart 8 inch floppy drives with enclosure and power supply cost me about $350.00. They were for my second computer. My first computer had no drives at all.
In 1973 IBM shipped the model 3340 Winchester sealed hard disk drive, the predecessor of all current hard disk drives. The 3340 had two spindles each with a capacity of 30 MBytes, and the term "30/30 Winchester" was thus coined.What is an IDE Hard Disk Drive?
Integrated Drive Electronics (IDE) hard disks have been around for quite a few years. Prior to these drives, hard disks were interfaced to a PC motherboard via an expansion board known as a hard disk controller. The drive did most of the mechanical stuff and performed basic electronic/servo functions; the controller told it in detail what to do. The development of the IDE hard moved most of the electronics and firmware (low-level software on a chip) from the controller to a printed circuit board on the drive itself. In the process, a buffer/cache' memory was added to the electronics to speed-up the process of reading and writing hard disk drive data. The drive got "smarter." 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. The term IDE Controller is a misnomer. It is actually nothing more than a bus interface and an interface and connector for the IDE cable going to the drive. The actual controller is on the drive. In most cases when a computer says it has a problem with the hard disk controller, it has a problem with the electronics on the drive. 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 Primary and a Secondary--each of which can support two IDE devices. The term Integrated Drive Electronics (IDE) is owned by Western Digital. Other companies, such as Maxtor, Quantum, and Seagate, use the term ATA (AT Attachment). IDE and ATA are the same thing. 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: Enhanced IDE (EIDE), ATAPI (ATA Packet Interface), Ultra-ATA, etc. Today, most hard disk drives manufactured for PCs are ATA/66 drives (ATA/100 is proably around the corner). These drives use Bus Mastering and Direct Memory Access to transfer data back and forth between the disk drive and the computer memory with burst speeds up to a theoretical 66 Mega Bytes per second (MBs) without going through the processor. Older ATA/33 (Ultra DMA) drives do the same thing at 33 MBs. Many existing motherboards still have ATA/33 or even older IDE interfaces. Most ATA/66 drives will work on the older IDE interfaces, but, of course, not as fast. The other major category of disk drives use variations of the Small Computer System Interface (SCSI) and will not be covered in the first publication of this guide
How a Hard Disk Drive Works
HARD DISK ASSEMBLY
A 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 the data structure of a hard disk is arranged into concentric circles instead of in a spiral as it on a phonograph record (and CD-ROM). 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 those in most of the drives I've dissected 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.
In 1980, Seagate Technology introduced the first hard disk drive for microcomputers, the ST506. 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. My first hard disk drive was an ST506. I cannot remember exactly how much it cost, but it plus its enclosure, etc. was well over a thousand dollars. It took me three years to fill the drive. Also, in 1980 Phillips introduced the first optical laser drive. In the early 80's, the first 5 1/4" hard disks with voice coil actuators (more on this later) started shipping in volume, but stepper motor drives continued in production into the early 1990's. In
1981, Sony shipped the first 3 1/2" floppy drives.
In 1983 Rodime made the first 3.5 inch rigid disk drive. The first CD-ROM drives were shipped in 1984, and "Grolier's Electronic Encyclopedia," followed in 1985. The 3 1/2" IDE drive started its existence as a drive on a plug-in expansion board, or "hard card." The hard card included the drive on the controller which, in turn, evolved into Integrated Device Electronics (IDE) hard disk drive, where the controller became incorporated into the printed circuit on the bottom of the hard disk drive. Quantum made the first hard card in 1985.
In 1986 the first 3 /12" hard disks with voice coil actuators were introduced by Conner in volume, but half (1.6") and full height 5 1/4" drives persisted for several years. In 1988 Conner introduced the first one inch high 3 1/2" hard disk drives. In the same year PrairieTek shipped the first 2 1/2" hard disks
In 1997 Seagate introduced the first 7,200 RPM, Ultra ATA hard disk drive for desktop computers and in February of this year they introduced the first 15,000 RPM hard disk drive, the Cheetah X15. Milestones for IDE DMA, ATA/33, and ATA/66 drives follow:
1994 DMA, Mode 2 at 16.6 MB/s
1997 Ultra ATA/33 at 33.3 MB/s
1999 Ultra ATA/66 at 66.6 MB/s
6/20/00 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 an American quarter. The world's first gigabyte-capacity disk drive, the IBM 3380, introduced in 1980, was the size of a refrigerator, weighed 550 pounds (about 250 kg), and had a price tag of $40,000.
HEADS
The heads (or Winchester sliders) are spring-loaded airfoils and actually fly like an airplane above (or below) the surface of the platters at a distance measured in micro-inches. The air stream though which a head "fly" is caused by the motion of the platters spinning through the air inside the HDA. The platters drag the air along by friction. The higher pressure air between the heads and the platters is known as air bearing. The effect is somewhat like a puck in an air hockey game. The bottom of a head is called an air bearing surface. This sort of mechanism was introduced in the Winchester hard disk drive invented by IBM in 1973.
The heads are bonded to a metal suspension (or head arm), which is a small arm that holds the head in position above or beneath a disk. A head and suspension is called a head-gimbal assembly or HGA. The HGA's are stacked together Into a head-stack assembly, which is propelled across the disk surface by the actuator. The actuator on most recent hard disks employs a voice coil mechanism. It functions much like the voice coil in a loud speaker, thus its name. It consists of a curved magnet (or magnets--very strong ones) and a spring-loaded coil of fine wire which is attached to the read/write heads by head arms. The head arms are attached to, and pivot about an actuator shaft. When the drive electronics apply an electric current to the actuator coil, it interacts with the magnet and swings against the actuator spring. The heads rotate around the actuator shaft in the opposite direction of the coil movement, inward and outward from the center to the edges of the platters. If there is a power outage (e.g., you turn-off the computer) the spring, which counterbalances the electromagnetic force between the coil and magnet, takes over and automatically parks (lands them on skids or nanosliders--like pontoons on a sea plane) and locks the heads on a part of the platters called a landing zone (like an airport runway only curved) before they can crash (like an airplane) on, and mar that part of the surface of the platters where data is stored. When power is restored, the platters speed-up and the heads take off (like a tethered model airplane, except the ground moves--and those on the bottoms of the platters can fly up-side-
down) and start flying again--an extraordinary mechanism...
SATA HARD DISKS
Serial ATA (SATA, IPA: /ˈseɪtə/ or /ˈsætə/) is a computer bus primarily designed for transfer of data between a computer and storage devices (like hard disk drives or optical drives).
The main benefits are thinner cables that let air cooling work more efficiently, faster transfers, ability to remove or add devices while operating (hot swapping), and more reliable operation with tighter data integrity checks than the older Parallel ATA interface.
It was designed as a successor to the legacy Advanced Tehnology Attachment standard (ATA), and is expected to eventually replace the older technology (retroactively renamed Parallel ATA or PATA). Serial ATA adapters and devices communicate over a high-speed serial cable.
The standard interface for SATA controllers is Advanced Host Controller Interface (AHCI), which allows advanced features of SATA such as hot plug and Native Command Queuing (NCQ). If AHCI is not enabled by the motherboard and chipset, SATA controllers typically operate in "IDE emulation" mode which does not allow features of devices to be accessed that are not supported by the ATA/IDE standard. Windows device drivers that are labeled as SATA are usually running in IDE emulation mode unless they explicitly state that they are AHCI. Windows XP does not officially support AHCI although some proprietary device drivers may allow it.[citation needed] Windows Vista and the current versions of Mac OS X and Linux [1] have native support for AHCI.[citation needed]
SATA offers performance as high as 3.0 Gbit/sec per device with the current specification. SATA uses only 4 signal lines, allowing for much more compact (and less expensive) cables compared with PATA. It also offers new features such as hot-swapping and native command queuing. There is a special connector (eSATA) specified for external devices, and an optionally implemented provision for clips on internal connectors. SATA drives may be plugged into Serial Attached SCSI (SAS) controllers and communicate on the same physical cable as native SAS disks. SAS disks, however, may not be plugged into a SATA controller.
