Wednesday, November 14, 2007

Hard disk drive characteristics

Capacity of a hard disk drive is usually quoted in gigabytes. Older HDDs quoted their smaller capacities in megabytes.

The data transfer rate at the inner zone ranges from 44.2 MB/s to 74.5 MB/s, while the transfer rate at the outer zone ranges from 74.0 MB/s to 111.4 MB/s. An HDD's random access time ranges from 5 ms to 15 ms.

The physical size of a hard disk drive is quoted in inches. The majority of HDDs used in desktops today are 3.5 inches (9 cm) wide, while the majority of those used in laptops are 2.5 inches (6 cm) wide. As of early 2007, manufacturers have started selling SATA and SAS 2.5 inch drives for use in servers and desktops.

An increasingly common form factor is the 1.8 inches (5 cm) ATA-7 LIF form factor used inside digital audio players and subnotebooks, which provide up to 160GB storage capacity at low power consumption and are highly shock-resistant. A previous 1.8 inches (5 cm) HDD standard exists, for 2–5 GB sized disks that fit directly into a PC card expansion slot. From these, the smaller 1 inch (3 cm) form factor was evolved, which is designed to fit the dimensions of CF Type II, which is also usually used as storage for portable devices including digital cameras. 1 inch was a de facto form factor led by IBM's Microdrive, but is now generically called 1 inch due to other manufacturers producing similar products. There is also a 0.85 inch form factor produced by Toshiba for use in mobile phones and similar applications, including SD/MMC slot compatible HDDs optimized for video storage on 4G handsets.

The size designations are more nomenclature than descriptive. The names refer to the width of the disk inserted into the drive rather than the actual width of the entire drive. A 5.25 inches (13 cm) drive has an actual width of 5.75 inches (15 cm), a 3.5 inches (9 cm) drive 4 inches (10 cm), a 2.5 inches (6 cm) drive 2.75 inches (7 cm). A 1.8 inches (5 cm) drive can have different widths, depending on its form factor. A PCMCIA drive has a width of 54 mm, while an ATA-7 LIF form factor drive has a width of 53.85 mm.

A hard disk is defined to be at "full height" if its height is 3.25 inches (8 cm). It is "half height" at a height of 1.625 inches (4 cm). A "slim height" or "low profile" HDD has a height of 1 inch (3 cm). "Ultra low profile" drives can have heights of 0.75 inches (19 mm), 0.67 inches (17 mm), 0.49 inches (12 mm) or 0.37 inches (9 mm).

History of hard disk drives

The commercial usage of hard disk drives began in 1956 with the shipment of an IBM 305 RAMAC system including IBM Model 350 disk storage.

For many years, hard disk drives were large, cumbersome devices, more suited to use in the protected environment of a data center or large office than in a harsh industrial environment (due to their delicacy), or small office or home (due to their size and power consumption). Before the early 1980s, most hard disk drives had 8-inch (actually, 210 - 195 mm) or 14-inch platters, required an equipment rack or a large amount of floor space (especially the large removable-media drives, which were frequently comparable in size to washing machines), and in many cases needed high-amperage and/or three-phase power hookups due to the large motors they used. Because of this, hard disk drives were not commonly used with microcomputers until after 1980, when Seagate Technology introduced the ST-506, the first 5.25-inch hard drive, with a formatted capacity of 5 megabytes.

The capacity of hard drives has grown exponentially over time. With early personal computers, a drive with a 20 megabyte capacity was considered large. During the mid to late 1990s, when PCs were capable of storing not just text files and documents but pictures, music, and video, internal drives were made with 8 to 20 GB capacities. As of early 2007, desktop hard disk drives typically have a capacity of 100 to 500 gigabytes, while the largest-capacity drives are 1 terabyte.

1950s - 1970s

The IBM 350 Disk File, invented by Reynold Johnson, was introduced in 1956 with the IBM 305 RAMAC computer. This drive had fifty 24 inch platters, with a total capacity of five million characters. A single head assembly having two heads was used for access to all the platters, making the average access time very slow (just under 1 second).

The IBM 1301 Disk Storage Unit, announced in 1961, introduced the usage of a head for each data surface with the heads having self acting air bearings (flying heads).

The first disk drive to use removable media was the IBM 1311 drive, which used the IBM 1316 disk pack to store two million characters.

In 1973, IBM introduced the IBM 3340 "Winchester" disk drive, the first significant commercial use of low mass and low load heads with lubricated media. All modern disk drives now use this technology and/or derivatives thereof. During the 1980s, the term "Winchester" became a common description for all hard disk drives, though generally falling out of use during the 1990s. Project head designer/lead designer Kenneth Haughton named it after the Winchester 30-30 rifle after the developers called it the "30-30" because of it was planned to have two 30 MB spindles; however, the actual product shipped with two spindles for data modules of either 35 MB or 70 MB.

1980s - PC era

Internal drives became the system of choice on PCs in the 1980s. Most microcomputer hard disk drives in the early 1980s were not sold under their manufacturer's names, but by OEMs as part of larger peripherals (such as the Corvus Disk System and the Apple ProFile). The IBM PC/XT had an internal hard disk drive, however, and this started a trend toward buying "bare" drives (often by mail order) and installing them directly into a system.

External hard drives remained popular for much longer on the Apple Macintosh and other platforms. Every Mac made between 1986 and 1998 has a SCSI port on the back, making external expansion easy; also, "toaster" Macs did not have easily accessible hard drive bays (or, in the case of the Mac Plus, any hard drive bay at all), so on those models, external SCSI disks were the only reasonable option.


1950s - 1990s

First disk drive
1956 IBM 350 RAMAC – 5 Megabytes, fifty 24" disks

First use of zoned recording
1961 Bryant Computer 4240 – 90 Megabytes, twenty four 39" disks

First disk drive with air bearing heads
1962 IBM 1301 "Advanced Disk File" – 28 Megabytes, twenty five 24" disks

First 14" disk drive and first with removable disk pack
1963 IBM 1311 "Low Cost File" – 2.69 Megabytes, six 14" disks

First voice coil actuator, first single disk cartridge drive
1965 IBM 2310 "Ramkit" – 1.024 Megabytes, one 14" disk

First disk drive with ferrite core heads
1966 IBM 2314 -- 29.17 Megabytes, eleven 14" disks

First track-following servo system
1971 IBM 3330-1 "Merlin" – 100 Megabytes, eleven 14" disks

First flexible disk drive, read-only
1971 IBM 23FD "Minnow" -- .0816 Megabytes, one 8" disk

First flexible disk drive to set industry standard for 8 inch diskettes
1973 IBM 33FD "Igar" -- .156 Megabytes, one 8" disk

First disk drive with low mass heads, lubricated disks, sealed assembly
1973 IBM 3340 "Winchester" – 35 or 70 Megabytes, two or four 14 disks

First disk drive with rotary actuator
1975 IBM 62 GV "Gulliver" – 5 or 9 Megabytes, one 14" disk

Re-introduction of disk drive with fixed disk media
1976 IBM 3350 "Madrid" -- 317.5 Megabytes, eight 14" disks

First flexible disk drive with two sided recording
1976 IBM 43FD "Crystal" -- .568 Megabytes, one 8" disk

First 5.25 inch flexible disk drive
1976 Shugart Associates SA400 -- .2188 Megabytes, one 5.25" disk

First disk drive with thin film heads, and 2,7 encoding
1979 IBM 3370 "New File Project" – 571.4 Megabytes, seven 14" disks

First 8 inch rigid disk drive
1979 IBM 62PC "Piccolo" – 64.5 Megabytes, six 8" disks

First 10.5 inch rigid disk drive
1981 Fujitsu F6421 "Eagle" – 446 Megabytes, six 10.5" disks

First 5.25 inch rigid disk drive
1980 Seagate Technology ST506 – 5 Megabytes, four 5.25" disks

First 3.5 inch flexible disk drive
1981 Sony OA-D3OV -- .4375 Megabytes, one 3.5" disk

First 3.5 inch rigid disk drive
1983 Rodime RO 352 – 10 Megabytes, two 3.5" disks

First 9 inch rigid disk drive
1982 Control Data 9715-160 "FSD" – 150 Megabytes, six 9" disks

First 8 disk 5.25 inch disk drive, with in-hub motor
1983 Maxtor XT-1140 – 126 Megabytes, eight 5.25" disks

First 8.8 inch rigid disk drive
1984 Hitachi DK815-5 – 460 Megabytes, eight 8.8" disks

First disk drive mounted on card
1985 Quantum Hardcard – 10.5 Megabytes, one 3.5" disk

First voice coil actuator 3.5" disk drive
1986 Conner Peripherals CP340 – 40 Megabytes, two 3.5" disks

First one inch high 3.5" disk drive
1988 Conner Peripherals CP3022 – 21 Megabytes, one 3.5" disk

First 2.5 inch disk drive
1988 PrairieTek 220 – 20 Megabytes, two 2.5" disks

First 9.5 inch rigid disk drive
1988 Hitachi DKU-86i – 1,890 Megabytes, eight 9.5" disks

First disk drive with PRML encoding
1990 IBM 0681 "Redwing" – 857 Megabytes, twelve 5.25" disks

First disk drive using magnetoresistive heads
1991 IBM 0663 "Corsair" – 1,004 Megabytes, eight 3.5" disks

First 1.8 inch disk drive
1991 Integral Peripherals 1820 "Mustang" – 21.4 Megabytes, one 1.8" disk

First 1.8 inch PC Card disk drives
1992 Integral Peripherals 1841PA "Ranger" – 42.5 Megabytes, one 1.8" disk

First 1.3 inch disk drive
1992 Hewlett-Packard C3013A "Kittyhawk" – 21.4 Megabytes, two 1.3" disks

First 7,200 RPM disk drive
1993 Seagate Technology ST12550 "Barracuda" – 2,139 Megabytes, ten 3.5" disks

First 6.5" rigid disk drive
1993 Hitachi H-6588-314 – 2,920 Megabytes, eight 6.5" disks

First 3 inch rigid disk drive
1995 JTS N0640-2AR – 641.7 Megabytes, two 3" disks

First embedded servo flexible disk drive
1995 Iomega Zip 100 – 100 Megabytes, one 3.5" disk

First drive using giant magnetoresistive heads
1997 IBM Deskstar 16GP "Titan" – 16,800 Megabytes, five 3.5" disks

First 10,000 RPM disk drive
1997 Seagate Technology ST19101 "Cheetah 9" – 9,100 Megabytes, eight 3.5" disks

First 10,000 RPM drive with 3 inch disks
1998 Seagate Technology ST118202 "Cheetah 18" – 18,200 Megabytes, twelve 3" disks

First 12,000 RPM disk drive
1998 Hitachi DK3E1T-91 – 9,200 Megabytes, nine 2.5" disks

First one inch disk drive
1999 IBM "Microdrive" – 340 Megabytes, one 1" disk

First 15,000 RPM disk drive
2000 Seagate Technology ST318451 "Cheetah X15" – 18,350 Megabytes, three 2.5" disks

1980s to present day

* 1980 - The world's first gigabyte-capacity disk drive, the IBM 3380, was the size of a refrigerator, weighed 550 pounds (about 250 kg), and had a price tag of $40,000.
* 1986 - Standardization of SCSI
* 1989 - Jimmy Zhu and H. Neal Bertram from UCSD proposed exchange decoupled granular microstructure for thin film disk storage media, still used today.
* 1991 - 2.5-inch 100 megabyte hard drive
* 1991 - PRML Technology (Digital Read Channel with 'Partial Response Maximum Likelihood' algorithm)
* 1992 - first 1.3-inch hard disk drive - HP C3013A
* 1994 - IBM introduces Laser Textured Landing Zones (LZT)
* 1996 - IBM introduces GMR (Giant MR) Technology for read sensors
* 1998 - UltraDMA/33 and ATAPI standardized
* 1999 - IBM releases the Microdrive in 170 MB and 340 MB capacities
* 2002 - 137 GB addressing space barrier broken
* 2003 - Serial ATA introduced
* 2005 - First 500 GB hard drive shipping (Hitachi GST)
* 2005 - Serial ATA 3G standardized
* 2005 - Seagate introduces Tunnel MagnetoResistive Read Sensor (TMR) and Thermal Spacing Control
* 2005 - Introduction of faster SAS (Serial Attached SCSI)
* 2005 - Perpendicular recording introduced in consumer HDDs (Toshiba)
* 2006 - First 750 GB hard drive (Seagate)
* 2006 - First 200 GB 2.5" hard drive utilizing Perpendicular recording (Toshiba)
* 2006 - Seagate announces research into nanotube-lubricated HDDs with capacities of several terabits per square inch, making possible a 7.5 terabyte 3.5" HDD
* 2006 - Fujitsu develops heat-assisted magnetic recording (HAMR) that could one day achieve one terabit per square inch densities.
* 2007 - Hitachi GST introduces 1 terabyte hard drive

Capacity and access speed

Hard disk drives can store much more data than floppy disk drives and access and transmit it faster. In 2007, a typical enterprise, i.e. workstation HDD might store between 160 GB and 1 TB of data (as of local US market by July 2007), rotate at 7,200 or 10,000 revolutions per minute (RPM), and have a sequential media transfer rate of over 80 MB/s. The fastest enterprise HDDs spin at 15,000 rpm, and can achieve sequential media transfer speeds up to and beyond 110 MB/s. Mobile, i.e., Laptop HDDs, which are physically smaller than their desktop and enterprise counterparts, tend to be slower and have less capacity. In the 1990s, most spun at 4,200 rpm. In 2007, a typical mobile HDD spins at 5,400 rpm, with 7,200 rpm models available for a slight price premium.

The exponential increases in disk space and data access speeds of HDDs have enabled the commercial viability of consumer products that require large storage capacities, such as the TiVo personal video recorder and digital music players. In addition, the availability of vast amounts of cheap storage has made viable a variety of web-based systems with extraordinary capacity requirements, such as the search and email systems offered by companies like Google.

The main way to decrease access time is to increase rotational speed, while the main way to increase throughput and storage capacity is to increase areal density. A vice president of Seagate Technology projects a future growth in disk density of 40% per year. Access times have not kept up with throughput increases, which themselves have not kept up with growth in storage capacity.

As of 2006, disk drives include perpendicular recording technology, in the attempt to enhance recording density and throughput.

The first 3.5" HDD marketed as able to store 1 TB is the Hitachi Deskstar 7K1000. The drive contains five platters at approximately 200 GB each, providing 935.5 GiB of usable space. Hitachi has since been joined by Samsung and Seagate in the 1 TB drive market.

Capacity measurements

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). On ATA drives bigger than 8 gigabytes, the values are set to 16383 cylinder, 16 heads, 63 sectors for compatibility with older operating systems. It should be noted that the values for cylinder, head & sector reported by a modern drive are not the actual physical parameters since, amongst other things, with zone bit recording the number of sectors varies by zone.

Hard disk drive manufacturers specify disk capacity using the SI prefixes mega, giga, and tera and their abbreviations M, G and T, respectively. Byte is typically abbreviated B.

Operating systems frequently report capacity using the same abbreviations but in reference to binary-based units. For instance, the prefix mega in the context of data storage can mean 220 (1,048,576), which is approximately equal to the actual value of the SI prefix mega, 106 (1,000,000). Similar usage has been applied to prefixes of greater magnitude. This results in a discrepancy between the disk manufacturer's stated capacity and the apparent capacity of the drive when examined from the operating system.

The difference becomes much more noticeable in the multi-gigabyte range. For example, Microsoft Windows reports disk capacity both in decimal-based units to 12 or more significant digits and with binary-based units to 3 significant digits. Thus a disk specified by a disk manufacturer as a 30 GB disk might have its capacity reported by Windows 2000 both as "30,065,098,568 bytes" and "28.0 GB" The disk manufacturer used the SI definition of "giga", 109 to arrive at 30 GB; however, because the utilities provided by Windows define a gigabyte as 1,073,741,824 bytes (230 bytes, often referred to as a gibibyte, or GiB), the operating system reports capacity of the disk drive as 28.0 GB.

Monday, November 12, 2007

The technology and how does it works

HDDs record data by magnetizing a ferromagnetic material directionally, to represent either a 0 or a 1 binary digit. They read the data back by detecting the magnetization of the material. A typical HDD design consists of a spindle which holds one or more flat circular disks called platters, onto which the data is recorded. The platters are made from a non-magnetic material, usually glass or aluminum, and are coated with a thin layer of magnetic material. Older disks used iron(III) oxide as the magnetic material, but current disks use a cobalt-based alloy.

The platters are spun at very high speeds. Information is written to a platter as it rotates past mechanisms called read-and-write heads that operate very close over the magnetic surface. The read-and-write head is used to detect and modify the magnetization of the material immediately under it. There is one head for each magnetic platter surface on the spindle, mounted on a common arm. An actuator arm (or access arm) moves the heads on an arc (roughly radially) across the platters as they spin, allowing each head to access almost the entire surface of the platter as it spins. The arm is moved using a voice coil actuator or (in older designs) a stepper motor.

The magnetic surface of each platter is divided into many small sub-micrometre-sized magnetic regions, each of which is used to encode a single binary unit of information. In today's HDDs each of these magnetic regions is composed of a few hundred magnetic grains. Each magnetic region forms a magnetic dipole which generates a highly localized magnetic field nearby. The write head magnetizes a magnetic region by generating a strong local magnetic field nearby. Early HDDs used an electromagnet both to generate this field and to read the data by using electromagnetic induction. Later versions of inductive heads included metal in Gap (MIG) heads and thin film heads. In today's heads, the read and write elements are separate but in close proximity on the head portion of an actuator arm. The read element is typically magneto-resistive while the write element is typically thin-film inductive.

In modern drives, the small size of the magnetic regions creates the danger that their magnetic state be lost because of thermal effects. To counter this, the platters are coated with two parallel magnetic layers, separated by a 3-atom-thick layer of the non-magnetic element ruthenium, and the two layers are magnetized in opposite orientation, thus reinforcing each other. Another technology used to overcome thermal effects to allow greater recording densities is perpendicular recording, which has been used in some hard drives as of 2006.

Hard disk drives are sealed to prevent dust and other sources of contamination from interfering with the operation of the hard disks heads. The hard drives are not air tight, but rather utilize an extremely fine air filter, to allow for air inside the hard drive enclosure. The spinning of the disks causes the air to circulate forcing any particulates to become trapped on the filter. The same air currents also act as a gas bearing which enables the heads to float on a cushion of air above the surfaces of the disks.

Source: YouTube, wikipedia

Sunday, November 11, 2007

About Harddisk drive

A hard disk drive (HDD), commonly referred to as a hard drive, hard disk or fixed disk drive, is a non-volatile storage device which stores digitally encoded data on rapidly rotating platters with magnetic surfaces. Strictly speaking, "drive" refers to a device distinct from its medium, such as a tape drive and its tape, or a floppy disk drive and its floppy disk. Early HDDs had removable media; however, an HDD today is typically a sealed unit with fixed media.

HDDs were originally developed for use with computers. In the 21st century, applications for HDDs have expanded beyond computers to include digital video recorders, digital audio players, personal digital assistants, digital cameras, and video game consoles. In 2005 the first mobile phones to include HDDs were introduced by Samsung and Nokia. The need for large-scale, reliable storage, independent of a particular device, led to the introduction of configurations such as RAID arrays, network attached storage (NAS) systems and storage area network (SAN) systems that provide efficient and reliable access to large volumes of data.

Taken from wikipedia.