Thursday, July 15, 2010


1)SATA (Serial Advanced Technology Attachment)
2)PATA (Parallel advanced technology attachment)
3)SCSI (Small Computer System Interface)
4)SSD (Solid-state drive)


SATA drives are Serial ATA drives.They use a completely different connector than the PATA drives. In addition, SATA drives use a different power adapter than IDE drives, though adapters are easily attainable. SATA drives are thinner and supposedly have a faster data interface than PATA drives. However, this speed difference is often no distinguishable in PATA and SATA drives of the same rpm rating. SATA drives are more
efficient, though, and use less energy than the PATA drives.


A stands for Parallel Advanced Technology Attachment and is also known as an IDE drive.
The labels refer to the type of interface used to connect the hard drive to the motherboard.IDE drives use either a 40 or 80 wire cable with a wide 40-pin connector. Older, slower drives use the 40 wire cable, while faster drives use the 80 wire cable. Many PATA drives are being replaced with SATA drives.


SCSI, Small Computer System Interface drives,have a similar took to IDE drives. However, SCSI drives typically spin at a higher rate than IDE or SATA drives Where IDE and SATA drive normally spin at 7,200 rpm. SCSI drives spin at 10,000 to 15,000 rpm. There are
some SATA drives now,It all are describe as showing in figure...


Solid state drives, unlike PATA, SATA or SCSI drives, do not use moving parts. Normally drives use a spinning magnetic disk that stores information. However, solid state drives use semi-conductors. Because there are no moving parts, solid state drives are faster and are less likely to break down than other drives. Data access is near instant. These drives are currently more expensive than other drives.


It is used to rotate the actuator. It Moved by Stepper motor or voice coil.


It is used to store memory in magnetic form.It rotate at high speed 5200 to 7200 rmp (Rotation per minute) A hard disk drive is a non-volatile storage device that stores digitally encoded data on rapidly rotating rigid Platters with magnetic surfaces. Strictly speaking, "drive" refers to the motorized mechanical aspect that is distinct from its medium, such as a floppy disk drive and its floppy disk. Early HDDs had removablemedia; however, an HDD today is typically a sealed unit with fixed media.


The actuator has a read-write head at the end of actuator and under the tip. A thin printed-circuit cable connects the read-write head to the hub of the actuator.

There is a one head for each megnatic platter surface on the splindle.A typical HDD design consists of a spindle that holds the circular disks. The HDD's spindle system relies on air pressure inside the disk enclosure to support to disk rotate.

When the hard disk is rotating at that time vibration is, it useful to Absorb the vibration of the hard disk and increased hard disk’s life.

A latch is provided suitabl for forcing the the drive intoor out of engagement with the
computer against resistance from mounting guide rails and an electrical connector. The latch is also suitable for locking the drive securely in place when it is in use and for carrying the drive between computers.

Wednesday, July 14, 2010


Raw unformatted capacity of a hard disk drive is usually quoted with SI prefixes (metric system prefixes), incrementing by powers of 1000; today that usually means gigabytes (GB) and terabytes (TB). This is conventional for data speeds and memory sizes which are not inherently manufactured in power of two sizes, as RAM and Flash memory are. Hard disks by contrast have no inherent binary size as capacity is determined by number of heads, tracks and sectors.

This can cause some confusion because some operating systems may report the formatted capacity of a hard drive using binary prefix units which increment by powers of 1024.

A one terabyte (1 TB) disk drive would be expected to hold around 1 trillion bytes (1,000,000,000,000) or 1000 GB; and indeed most 1 TB hard drives will contain slightly more than this number. However some operating system utilities would report this as around 931 GB or 953,674 MB. (The actual number for a formatted capacity will be somewhat smaller still, depending on the file system). Following are the several ways of reporting one Terabyte.
SI prefixes (hard drive) equivalent Binary prefixes (OS) equivalent
1 TB (TERA BYTE) 1 * 10004 B 0.9095 TB (Terabyte) 0.9095 * 10244 B
1000 GB (GIGA BYTE) 1000 * 10003 B 931.3 GB (Gigabyte) 931.3 * 10243 B
1,000,000 MB (MEGA BYTE) 1,000,000 * 10002 B 953,674.3 MB(MB)953 674.3 *10242
1,000,000,000 KB (KILLO B) 1,000,000,000 * 1000B 976,562,500 KB (KB) 976,562,500*1024B
1,000,000,000,000 B (byte) 1,000,000,000,000 B (byte) -

Microsoft Windows reports disk capacity both in a decimal integer to 12 or more digits and in binary prefix units to three significant digits.

The capacity of an HDD can be calculated by multiplying the number of cylinders by the number of heads by the number of sectors by the number of bytes/sector (most commonly 512). Drives with the ATA interface and a capacity of eight gigabytes or more behave as if they were structured into 16383 cylinders, 16 heads, and 63 sectors, for compatibility with older operating systems. Unlike in the 1980s, the cylinder, head, sector (C/H/S) counts reported to the CPU by a modern ATA drive are no longer actual physical parameters since the reported numbers are constrained by historic operating-system interfaces and with zone bit recording the actual number of sectors varies by zone. Disks with SCSI interface address each sector with a unique integer number; the operating system remains ignorant of their head or cylinder count.

The old C/H/S scheme has been replaced by logical block addressing. In some cases, to try to "force-fit" the C/H/S scheme to large-capacity drives, the number of heads was given as 64, although no modern drive has anywhere near 32 platters.

For a formatted drive, the operating system's file system internal usage is another, although minor, reason why a computer hard drive or storage device's capacity may show its capacity as different from its theoretical capacity. This would include storage for, as examples, a file allocation table (FAT) or inodes, as well as other operating system data structures. This file system overhead is usually less than 1% on drives larger than 100 MB. For RAID drives, data integrity and fault-tolerance requirements also reduce the realized capacity. For example, a RAID1 drive will be about half the total capacity as a result of data mirroring. For RAID5 drives with x drives you would lose 1/x of your space to parity. RAID drives are multiple drives that appear to be one drive to the user, but provides some fault-tolerance.

A general rule of thumb to quickly convert the manufacturer's hard disk capacity to the standard Microsoft Windows formatted capacity is 0.93*capacity of HDD from manufacturer for HDDs less than a terabyte and 0.91*capacity of HDD from manufacturer for HDDs equal to or greater than 1 terabyte.


A typical hard drive has two electric motors, one to spin the disks and one to position the read/write head assembly. The disk motor has an external rotor attached to the platters; the stator windings are fixed in place. The actuator has a read-write head under the tip of its very end (near center); a thin printed-circuit cable connects the read-write head to the hub of the actuator. A flexible, somewhat 'U'-shaped, ribbon cable, seen edge-on below and to the left of the actuator arm in the first image and more clearly in the second, continues the connection from the head to the controller board on the opposite side.

The head support arm is very light, but also rigid; in modern drives, acceleration at the head reaches 550 Gs.

The silver-colored structure at the upper left of the first image is the top plate of the permanent-magnet and moving coil motor that swings the heads to the desired position (it is shown removed in the second image). The plate supports a thin neodymium-iron-boron (NIB) high-flux magnet. Beneath this plate is the moving coil, often referred to as the voice coil by analogy to the coil in loudspeakers, which is attached to the actuator hub, and beneath that is a second NIB magnet, mounted on the bottom plate of the motor (some drives only have one magnet).

The voice coil itself is shaped rather like an arrowhead, and made of doubly coated copper magnet wire. The inner layer is insulation, and the outer is thermoplastic, which bonds the coil together after it's wound on a form, making it self-supporting. The portions of the coil along the two sides of the arrowhead (which point to the actuator bearing center) interact with the magnetic field, developing a tangential force that rotates the actuator. Current flowing radially outward along one side of the arrowhead and radially inward on the other produces the tangential force. If the magnetic field were uniform, each side would generate opposing forces that would cancel each other out. Therefore the surface of the magnet is half N pole, half S pole, with the radial dividing line in the middle, causing the two sides of the coil to see opposite magnetic fields and produce forces that add instead of canceling. Currents along the top and bottom of the coil produce radial forces that do not rotate the head.


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.

Seagate ST4053 40 MByte
5 1/4 inch, full-height "clunker"
with ST506 interface and voice coil
circa 1987. My cost was $435.00.

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.