HARD DISK DRIVE GUIDE 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. 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 Seagate ST4053 40 MByte 5 1/4 inch, full-height "clunker" with ST506 interface and voice coil circa 1987. My cost was $435.00.
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HARD DISK DRIVE GUIDE
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.
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
Seagate ST4053 40 MByte
5 1/4 inch, full-height "clunker"
with ST506 interface and voice coil
circa 1987. My cost was $435.00.
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
Present serial ATA (SATA) are using
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.
HARD DISK DRIVE GUIDE
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.
HARD DISK DRIVE GUIDE
How a Hard Disk Drive Works Hard Disk Assembly
The purpose of this article is to provide just the right balance of technical detail to convey a good
insight into the innards of a hard disk drive and how if basically works without burdening the
reader with excessive technical detail.
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.
HARD DISK DRIVE GUIDE
How a Hard Disk Drive Works Heads
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 extremely small electromagnets (about 1 mm square) and
one is shown schematically to the right. 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 (little bitty, molecular magnets) on a particular spot on
the platter's magnetic coating, and, thus, whether the spot represents a
binary one or zero. The domains essentially retain their directional bent
(whether the computer is on or off) until "told" to do otherwise by the
drive electronics, which take their orders from the rest of the computer and ultimately from
software. The complexity of the mechanisms and methods associated with doing all of this will
be omitted here.
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...
One no longer has to park a hard disk before moving the computer as was the case in times of old
when actuators were moved by devices known as stepper motors. However, if the power jitters
repeatedly or the drive is subjected whack from a frustrated user, a crash can occur.
HARD DISK DRIVE GUIDE
How a Hard Disk Drive Works Servo-Formatting
SERVO-FORMATTING. Try to visualize a
thin, hollow cylinder passing through all of the
platters in a hard disk drive. It would produce a
circular track on each side of each platter. Now
divide each tack into equal arcs or sectors. Well,
that is exactly how a hard disk is organized. That
is, Cylinders, Heads (which are equal the number
of tracks/cylinder or platter sides), and Sectors are
the coordinates of the data on a hard disk drive.
There are two kinds of sectors on a hard disk.
The first and at the very lowest level is the servo
sector. When a hard disk is manufactured a
special pattern is written in a code called a Gray
code on the surface of the platters, while the drive
is open in a clean room, with an expensive
machine called a servowriter.
A Gray Code is a binary code in which successive numbers differ by only a single bit.
Although many Gray Codes are possible, one specific Gray Code is considered the Gray
Code because of its efficiency in computation. This efficiency is why it is used for the servo
pattern instead of other binary codes. A three-bit Gray Code is shown to the right.
Although there are other schemes, the Gray Code is written in a wedge at the start of each
sector (an embedded servo pattern) on most drives. There are a fixed number of servo
sectors per track and the sectors are adjacent to one another. This pattern is permanent and
cannot be changed by writing normal data to the drive. It also cannot be changed by low-
level formatting (see below) the drive, as some may think. If it is changed, the drive has had
it--kaput!
The electronics use feedback from the heads, which read the Gray code pattern, to very
accurately position, and constantly correct the radial position of the appropriate head over the
desired track, at the beginning of each sector, to compensate for variations in platter geometry,
caused by mechanical stress and thermo expansion and contraction. Altogether, the head
000
001
011
010
110
111
101
100
positioning components form what is know as closed-loop servo system--a marvelous (and,
perhaps, dangerous) thing to watch operate in a drive which has been open.
Timeline: 50 Years of Hard Drives
Over the past five decades, hard drives have come a long way. Travel through time with us as we
chronicle 50 milestones in hard-drive development--from product firsts to new technologies, and
everything in between.
Photograph: Courtesy of Hitachi GST
1956: IBM ships the first hard drive in the RAMAC 305 system. The drive holds 5MB of data at
$10,000 a megabyte. The system is as big as two refrigerators and uses 50 24-inch platters. (For
the full story and interviews with key players, read "The Hard Drive Turns 50.")
1961: IBM invents heads for disk drives that "fly" on a cushion of air or on "air bearings."
1963: IBM comes up with the first removable hard drive, the 1311, which has six 14-inch
platters and holds 2.6MB.
1966: IBM introduces the first drive using a wound-coil ferrite recording head.
1970: General Digital Corporation (renamed Western Digital in 1971) is founded in California.
Photograph: Courtesy of Hitachi GST
1973: IBM announces the 3340, the first modern "Winchester" hard drive, which has a sealed
assembly, lubricated spindles, and low-mass heads.
