INSTITUTION OF CONTINUING EDUCATION (I.C.E)
RIVERS STATE COLLEGE OF ARTS AND SCIENCE
RUMUOLA, PORT HARCOURT.

NAME: JOSHUA JAKES DEPARTMENT: SAFETY AND SECURITY MANAGEMENT

COURSE TITLE: HEALTH RELATED PROBLEMS IN WORK PLACES

COURSES CODE: KSS 207

Assignment on.
Explain 5 ways were by management can promote and Maintain the health of workers
JUNE, 2014

Hard disk drive
"Hard drive" redirects here. For other uses,. | A 2.5" SATA hard drive | | | Invented by | |

A disassembled and labeled 1997 HDD laying atop a mirror.

Overview of how an HDD functions
A hard disk drive (HDD)[b] is a data storage device used for storing and retrieving digital information using rapidly rotating disks (platters) coated with magnetic material.[2] An HDD retains its data even when powered off. Data is read in a random-access manner, meaning individual blocks of data can be stored or retrieved in any order rather than sequentially. An HDD consists of one or more rigid ("hard") rapidly rotating disks (platters) with magnetic heads arranged on a moving actuator arm to read and write data to the surfaces.
Introduced by IBM in 1956,[3] HDDs became the dominant secondary storage device for general purpose computers by the early 1960s. Continuously improved, HDDs have maintained this position into the modern era of servers and personal computers. More than 200 companies have produced HDD units, though most current units are manufactured by Seagate, Toshiba and Western Digital. Worldwide revenues for HDD shipments are expected to reach US $33 billion in 2013, a decrease of approximately 12% from US $37.8 billion in 2012.
The primary characteristics of an HDD are its capacity and performance. Capacity is specified in unit prefixes corresponding to powers of 1000: a 1-terabyte (TB) drive has a capacity of 1,000 gigabytes (GB; where 1 gigabyte = 1 billion bytes). Typically, some of an HDD's capacity is unavailable to the user because it is used by the file system and the computer operating system, and possibly inbuilt redundancy for error correction and recovery. Performance is specified by the time to move the heads to a file (Average Access Time) plus the time it takes for the file to move under its head (average latency, a function of the physical rotational speed in revolutions per minute) and the speed at which the file is transmitted (data rate).
The two most common form factors for modern HDDs are 3.5-inch in desktop computers and 2.5-inch in laptops. HDDs are connected to systems by standard interface cables such as SATA (Serial ATA), USB or SAS (Serial attached SCSI) cables.
As of 2014, the primary competing technology for secondary storage is flash memory in the form of solid-state drives (SSDs). HDDs are expected to remain the dominant medium for secondary storage due to predicted continuing advantages in recording capacity, price per unit of storage, write latency and product lifetime.[4][5] However, SSDs are replacing HDDs where speed, power consumption and durability are more important considerations.[6][7]

Video of modern HDD operation (cover removed)
Main article: History of hard disk drives
HDDs were introduced in 1956 as data storage for an IBM real-time transaction processing computer[3] and were developed for use with general purpose mainframe and minicomputers. The first IBM drive, the 350 RAMAC, was approximately the size of two refrigerators and stored 5 million 6-bit characters (3.75 megabytes) on a stack of 50 disks.
In 1961 IBM introduced the model 1311 disk drive, which was about the size of a washing machine and stored two million characters on a removable disk pack. Users could buy additional packs and interchange them as needed, much like reels of magnetic tape. Later models of removable pack drives, from IBM and others, became the norm in most computer installations and reached capacities of 300 megabytes by the early 1980s. Non-removable HDDs were called "fixed disk" drives.
Some high performance HDDs were manufactured with one head per track, e.g., IBM 2305 so that no time was lost physically moving the heads to a track.[8] Known as Fixed-Head or Head-Per-Track disk drives they were very expensive and are no longer in production.[9]
In 1973, IBM introduced a new type of HDD codenamed "Winchester". Its primary distinguishing feature was that the disk heads were not withdrawn completely from the stack of disk platters when the drive was powered down. Instead, the heads were allowed to "land" on a special area of the disk surface upon spin-down, "taking off" again when the disk was later powered on. This greatly reduced the cost of the head actuator mechanism, but precluded removing just the disks from the drive as was done with the disk packs of the day. Instead, the first models of "Winchester technology" drives featured a removable disk module, which included both the disk pack and the head assembly, leaving the actuator motor in the drive upon removal. Later "Winchester" drives abandoned the removable media concept and returned to non-removable platters.
Like the first removable pack drive, the first "Winchester" drives used platters 14 inches (360 mm) in diameter. A few years later, designers were exploring the possibility that physically smaller platters might offer advantages. Drives with non-removable eight-inch platters appeared, and then drives that used a 5 1⁄4 in (130 mm) form factor (a mounting width equivalent to that used by contemporary floppy disk drives). The latter were primarily intended for the then-fledgling personal computer (PC) market.
As the 1980s began, HDDs were a rare and very expensive additional feature on PCs; however by the late 1980s, their cost had been reduced to the point where they were standard on all but the cheapest PC.
Most HDDs in the early 1980s were sold to PC end users as an external, add-on subsystem. The subsystem was not sold under the drive manufacturer's name but under the subsystem manufacturer's name such as Corvus Systems and Tallgrass Technologies, or under the PC system manufacturer's name such as the Apple ProFile. The IBM PC/XT in 1983 included an internal 10 MB HDD, and soon thereafter internal HDDs proliferated on personal computers.
External HDDs remained popular for much longer on the Apple Macintosh. Every Mac made between 1986 and 1998 has a SCSI port on the back, making external expansion easy; also, "toaster" Compact Macs did not have easily accessible HDD 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.
The 2011 Thailand floods damaged manufacturing plants, and impacted hard disk drive cost adversely in 2011-2013.[10]
Driven by areal density doubling every two to four years since their invention (an observation known as Kryder's law, similar to Moore's Law), HDDs have continuously improved their characteristics; a few highlights include: * Capacity per HDD increasing from 3.75 megabytes to 4 terabytes or more, more than a million times larger. * Physical volume of HDD decreasing from 68 cubic feet (1.9 m3) (comparable to a large side-by-side refrigerator), to less than 20 cubic centimetres (1.2 cu in), a 100,000-to-1 decrease. * Weight decreasing from 2,000 pounds (910 kg) to 48 grams (1.7 oz),[11] a 20,000-to-1 decrease. * Price decreasing from about US$15,000 per megabyte to less than $0.00006 per megabyte ($90/1.5 terabyte), a greater than 250-million-to-1 decrease. * Average Access Time decreasing from over 100 milliseconds to a few milliseconds, a greater than 40-to-1 improvement. * Market application expanding from mainframe computers of the late 1950s to most mass storage applications including computers and consumer applications such as storage of entertainment content.
Technology

Magnetic recording
An HDD records data by magnetizing a thin film of ferromagnetic material[c] on a disk. Sequential changes in the direction of magnetization represent binary data bits. The data is read from the disk by detecting the transitions in magnetization. User data is encoded using an encoding scheme, such as run-length limited encoding,[d] which determines how the data is represented by the magnetic transitions.
A typical HDD design consists of a spindle that holds flat circular disks, also called platters, which hold the recorded data. The platters are made from a non-magnetic material, usually aluminium alloy, glass, or ceramic, and are coated with a shallow layer of magnetic material typically 10–20 nm in depth, with an outer layer of carbon for protection.[15][16][17] For reference, a standard piece of copy paper is 0.07–0.18 millimetres (70,000–180,000 nm).[18]

Diagram labeling the major components of a computer HDD

Recording of single magnetisations of bits on a 200 MB HDD-platter (recording made visible using CMOS-MagView).[19]

Longitudinal recording (standard) & perpendicular recording diagram
The platters in contemporary HDDs are spun at speeds varying from 4,200 rpm in energy-efficient portable devices, to 15,000 rpm for high-performance servers.[20] The first HDDs spun at 1,200 rpm[3] and, for many years, 3,600 rpm was the norm.[21] As of December 2013, the platters in most consumer-grade HDDs spin at either 5,400 rpm or 7,200 rpm.
Information is written to and read from a platter as it rotates past devices called read-and-write heads that operate very close (often tens of nanometers) over the magnetic surface. The read-and-write head is used to detect and modify the magnetization of the material immediately under it.
In modern drives 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 some older designs a stepper motor. Early hard disk drives wrote data at some constant bits per second, resulting in all tracks having the same amount of data per track but modern drives (since the 1990s) use zone bit recording—increasing the write speed from inner to outer zone and thereby storing more data per track in the outer zones.
In modern drives, the small size of the magnetic regions creates the danger that their magnetic state might be lost because of thermal effects, thermally induced magnetic instability which is commonly known as the "super paramagnetic." To counter this, the platters are coated with two parallel magnetic layers, separated by a 3-atom layer of the non-magnetic element ruthenium, and the two layers are magnetized in opposite orientation, thus reinforcing each other.[22] Another technology used to overcome thermal effects to allow greater recording densities is perpendicular recording, first shipped in 2005,[23] and as of 2007 the technology was used in many HDDs.[24][25][26]
Components

HDD with disks and motor hub removed exposing copper colored stator coils surrounding a bearing in the center of the spindle motor. Orange stripe along the side of the arm is thin printed-circuit cable, spindle bearing is in the center and the actuator is in the upper left
A typical HDD has two electric motors; a spindle motor that spins the disks and an actuator (motor) that positions the read/write head assembly across the spinning disks. The disk motor has an external rotor attached to the disks; the stator windings are fixed in place. Opposite the actuator at the end of the head support arm is the read-write head; thin printed-circuit cables connect the read-write heads to amplifier electronics mounted at the pivot of the actuator. The head support arm is very light, but also stiff; in modern drives, acceleration at the head reaches 550 g.

Head stack with an actuator coil on the left and read/write heads on the right
The actuator is a permanent magnet and moving coil motor that swings the heads to the desired position. A metal plate supports a squat 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 is 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 HDD's electronics control the movement of the actuator and the rotation of the disk, and perform reads and writes on demand from the disk controller. Feedback of the drive electronics is accomplished by means of special segments of the disk dedicated to servo feedback. These are either complete concentric circles (in the case of dedicated servo technology), or segments interspersed with real data (in the case of embedded servo technology). The servo feedback optimizes the signal to noise ratio of the GMR sensors by adjusting the voice-coil of the actuated arm. The spinning of the disk also uses a servo motor. Modern disk firmware is capable of scheduling reads and writes efficiently on the platter surfaces and remapping sectors of the media which have failed.
Error rates and handling
Modern drives make extensive use of error correction codes (ECCs), particularly Reed–Solomon error correction. These techniques store extra bits, determined by mathematical formulas, for each block of data; the extra bits allow many errors to be corrected invisibly. The extra bits themselves take up space on the HDD, but allow higher recording densities to be employed without causing uncorrectable errors, resulting in much larger storage capacity.[27] For example, a typical 1 TB hard disk with 512-byte sectors provides additional capacity of about 93 GB for the ECC data.[28]
In the newest drives, as of 2009, low-density parity-check codes (LDPC) were supplanting Reed-Solomon; LDPC codes enable performance close to the Shannon Limit and thus provide the highest storage density available.[29]
Typical hard disk drives attempt to "remap" the data in a physical sector that is failing to a spare physical sector provided by the drive's "spare sector pool" (also called "reserve pool"),[30] while relying on the ECC to recover stored data while the amount of errors in a bad sector is still low enough. The S.M.A.R.T (Self-Monitoring, Analysis and Reporting Technology) feature counts the total number of errors in the entire HDD fixed by ECC (although not on all hard drives as the related S.M.A.R.T attributes "Hardware ECC Recovered" and "Soft ECC Correction" are not consistently supported), and the total number of performed sector remappings, as the occurrence of many such errors may predict an HDD failure.
The "No-ID Format", developed by IBM in the mid-1990s, contains information about which sectors are bad and where remapped sectors have been located.[31]
Only a tiny fraction of the detected errors ends up as not correctable. For example, specification for an enterprise SAS disk (a model from 2013) estimates this fraction to be one uncorrected error in every 1016 bits,[32] and another SAS enterprise disk from 2013 specifies similar error rates.[33] Another modern (as of 2013) enterprise SATA disk specifies an error rate of less than 10 non-recoverable read errors in every 1016 bits.[34] An enterprise disk with a Fibre Channel interface, which uses 520 byte sectors to support the Data Integrity Field standard to combat data corruption, specifies similar error rates in 2005.[35]
The worst type of errors are those that go unnoticed, and are not even detected by the disk firmware or the host operating system. These errors are known as silent data corruption, some of which may be caused by hard disk drive malfunctions.[36]
Future development
HDD areal density has shown a long term compound annual growth rate (1956 - 2010) somewhat higher than the 41% per year Moore's Law growth;[37] most recently growth has been in the range of 8–12% annually[38][39] However beginning around 2010, the super paramagnetic limit constrained the rate of progress.[39] According to industry observers and analysts for 2011 to 2016 and beyond, the areal density compound annual growth is forecasted to be 19,[40] 25%[41] or 20-40%[42] per year.
New magnetic storage technologies are being developed to support higher areal density growth, address the super paramagnetic limit, and maintain the competitiveness of HDDs with respect to products such as flash memory-based solid-state drives (SSDs). One of several such technologies, Shingled magnetic recording, was introduced in 2013 as the first step to reaching a 20 TB HDD by 2020.[43] Other new HDD technologies still in the laboratory include heat-assisted magnetic recording (HAMR),[44][45] bit-patterned recording (BPR)[46] and "current perpendicular to plane" giant magneto resistance (CPP/GMR) heads.[41][47]
File system use
The presentation of an HDD to its host is determined by its controller. This may differ substantially from the drive's native interface particularly in mainframes or servers.
Modern HDDs, such as SAS[48] and SATA[49] drives, appear at their interfaces as a contiguous set of logical blocks; typically 512 bytes long but the industry is in the process of changing to 4,096-byte logical blocks; see Advanced Format.[51]
The process of initializing these logical blocks on the physical disk platters is called low level formatting which is usually performed at the factory and is not normally changed in the field.[e]
In the case of "mega-", there is a nearly 5% difference between the powers of 1,000 definition and the powers of 1,024 definition. Furthermore, the difference is compounded by 2.4% with each incrementally larger prefix (gigabyte, terabyte, etc.). The discrepancy between the two conventions for measuring capacity was the subject of several class action suits against HDD manufacturers. The plaintiffs argued that the use of decimal measurements effectively misled consumers[65][66] while the defendants denied any wrongdoing or liability, asserting that their marketing and advertising complied in all respects with the law and that no class member sustained any damages or injuries.[67]
In December 1998, standards organizations addressed these dual definitions of the conventional prefixes by standardizing on unique binary prefixes and prefix symbols to denote multiples of 1,024, such as "mebibyte (MiB)", which exclusively denotes 220 or 1,048,576 bytes.[68] This standard has seen little adoption by the computer industry, and the conventionally prefixed forms of "byte" continue to denote slightly different values depending on context.[69][70]

Six HDDs with 8", 5.25", 3.5", 2.5", 1.8", and 1" hard disks with a ruler to show the length of platters and read-write heads
Mainframe and minicomputer hard disks were of widely varying dimensions, typically in free standing cabinets the size of washing machines or designed to fit a 19" rack. In 1962, IBM introduced its model 1311 disk, which used 14 inch (nominal size) platters. This became a standard size for mainframe and minicomputer drives for many years.[87] Such large platters were never used with microprocessor-based systems.
With increasing sales of microcomputers having built in floppy-disk drives (FDDs), HDDs that would fit to the FDD mountings became desirable. Thus HDD Form factors, initially followed those of 8-inch, 5.25-inch, and 3.5-inch floppy disk drives. Because there were no smaller floppy disk drives, smaller HDD form factors developed from product offerings or industry standards.

Smallest HDD.

5¼" full height 110 MB HDD; 2½" (63.5 mm) 6,495 MB HDD
As of 2012, 2.5-inch and 3.5-inch hard disks were the most popular sizes.
By 2009 all manufacturers had discontinued the development of new products for the 1.3-inch, 1-inch and 0.85-inch form factors due to falling prices of flash memory,[105][106] which has no moving parts.
While these sizes are customarily described by an approximately correct figure in inches, actual sizes have long been specified in millimeters.

Access and interfaces

HDDs are accessed over one of a number of bus types, including as of 2011 parallel ATA (PATA, also called IDE or EIDE; described before the introduction of SATA as ATA), Serial ATA (SATA), SCSI, Serial Attached SCSI (SAS), and Fibre Channel. Bridge circuitry is sometimes used to connect HDDs to buses with which they cannot communicate natively, such as IEEE 1394, USB and SCSI.
Integrity and failure

Close-up of an HDD head resting on a disk platter; its mirror reflection is visible on the platter surface.
Due to the extremely close spacing between the heads and the disk surface, HDDs are vulnerable to being damaged by a head crash—a failure of the disk in which the head scrapes across the platter surface, often grinding away the thin magnetic film and causing data loss. Head crashes can be caused by electronic failure, a sudden power failure, physical shock, contamination of the drive's internal enclosure, wear and tear, corrosion, or poorly manufactured platters and heads.
The HDD's spindle system relies on air density inside the disk enclosure to support the heads at their proper flying height while the disk rotates. HDDs require a certain range of air densities in order to operate properly. The connection to the external environment and density occurs through a small hole in the enclosure (about 0.5 mm in breadth), usually with a filter on the inside (the breather filter).[115] If the air density is too low, then there is not enough lift for the flying head, so the head gets too close to the disk, and there is a risk of head crashes and data loss. Specially manufactured sealed and pressurized disks are needed for reliable high-altitude operation, above about 3,000 m (9,800 ft).[116] Modern disks include temperature sensors and adjust their operation to the operating environment. Breather holes can be seen on all disk drives—they usually have a sticker next to them, warning the user not to cover the holes. The air inside the operating drive is constantly moving too, being swept in motion by friction with the spinning platters. This air passes through an internal recirculation (or "recirc") filter to remove any leftover contaminants from manufacture, any particles or chemicals that may have somehow entered the enclosure, and any particles or outgassing generated internally in normal operation. Very high humidity present for extended periods of time can corrode the heads and platters.
External hard disk drives
See also: USB mass storage / USB drive and Disk enclosure

Toshiba 1 TB 2.5" external USB 2.0 HDD

3.0 TB 3.5" Seagate FreeAgent GoFlex plug and play external USB 3.0-compatible drive (left), 750 GB 3.5" Seagate Technology push-button external USB 2.0 drive (right), and a 500 GB 2.5" generic brand plug and play external USB 2.0 drive (front).
External HDDs[k] typically connect via USB; variants using USB 2.0 interface generally have slower data transfer rates when compared to internally mounted hard drives connected through SATA. Plug and play drive functionality offers system compatibility and features large storage options and portable design.
External HDDs are usually available as pre-assembled integrated products, but may be also assembled by combining an external enclosure (with USB or other interface) with a separately purchased HDD. They are available in 2.5-inch and 3.5-inch sizes; 2.5-inch variants are typically called portable external drives, while 3.5-inch variants are referred to as desktop external drives. "Portable" drives are packaged in smaller and lighter enclosures than the "desktop" drives; additionally, "portable" drives use power provided by the USB connection, while "desktop" drives require external power bricks.
As of April 2014, capacities of external HDDs generally range from 160 GB to 6 TB; common sizes are 160 GB, 250 GB, 320 GB, 500 GB, 640 GB, 750 GB, 1 TB, 2 TB, 3 TB, 4 TB, 5 TB and 6 TB.[126][127] Features such as biometric security or multiple interfaces (for example, Firewire) are available at a higher cost.[128]
There are pre-assembled external hard disk drives that, when taken out from their enclosures, cannot be used internally in a laptop or desktop computer due to embedded USB interface on their printed circuit boards, and lack of SATA (or Parallel ATA) interfaces.[129][130]
Icons
HDDs are traditionally symbolized as a stylized stack of platters or as a cylinder and are found in diagrams, or on lights to indicate HDD access. In most modern operating systems, HDDs are represented by an illustration or photograph of the drive enclosure. *
HDDs are commonly symbolized with a drive icon *
RAID diagram icon symbolizing the array of disks

References 1. Kean, David W., "IBM San Jose, A quarter century of innovation", 1977. 2. Arpaci-Dusseau, Remzi H.; Arpaci-Dusseau, Andrea C. (2014). "Operating Systems: Three Easy Pieces [Chapter: Hard Disk Drives]". Arpaci-Dusseau Books. 3. "IBM Archives: IBM 350 disk storage unit". Retrieved 2012-10-19. 4. Fullerton, Eric (March 2014). "5th Non-Volatile Memories Workshop (NVMW 2014)". IEEE. Retrieved April 23, 2014. 5. Handy, James (July 31, 2012). "For the Lack of a Fab.". Objective Analysis. Retrieved November 25, 2012. 6. Hutchinson, Lee. (2012-06-25) How SSDs conquered mobile devices and modern OSes. Ars Technica. Retrieved on 2013-01-07. 7. Santo Domingo, Joel (May 10, 2012). "SSD vs HDD: What's the Difference?". PC Magazine. Retrieved November 24, 2012. 8. Microsoft Windows NT Workstation 4.0 Resource Guide © 1995, Chapter 17 – Disk and File System Basics 9. Computer Organization and Design, 2nd Ed., P. Pal Chaudhuri, © 2006,p. 635 10. "Farming hard drives: how Backblaze weathered the Thailand drive crisis". blaze.com. 2013. Retrieved 2014-05-23.