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Keys on a computer keyboard
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Modifier key: Control key – Shift key, Alt key / Option key (Macintosh), AltGr key, Command key / Meta key (MIT computer keyboards), Windows key, Fn key (compact keyboard layout); Dead key – Compose key; Lock key – Scroll lock, Num lock, Caps lock; Navigation keys – Arrow keys, Page scroll keys (Page up key / Page down key), Home key / End key; Edit keys – Return key / Enter key, Backspace, Insert key, Delete key, Tab key; SysRq / Print screen; Break key / Pause key; Escape key; Menu key; Space bar; Numeric keypad; Function key; Power management keys.
Assignments
Task III. Give equivalent of the following computer word combs with nouns used as modifiers.
Web Browser; e-mail client; connection types; wireless keyboards; game controllers; side effect; key unlocking; circuit design.
Task IV. Translate & remember the following phrases, make sentences of your own, using these phrases:
Prior to …; to pose a security problem; due to …; to project image on a surface; to be purposed for; to be easily pressed by fingers; to be designed for …; it does not matter; to type commands to a computer; options for handling currently running applications; for instance; for example.
Task V. Topics for discussion:
1. Dwell on main trends in keyboards designs.
2. Describe the different keyboards their advantages and disadvantages.
Task VI. What do the following acronyms stand for? Match the equivalents.
ADD, USB
Unit 6. Hard disk
Task I. Key vocabulary.
Find the Russian equivalents of the following words and word combinations:
The actuator arm, spindle, grain, thin film head, sequential, transfer, storage capacity, amount of data, to contain, a discrepancy, utilities, to provide, standard binary prefix, to occupy, therefore, account for, apparent, the appearance, especially, to seal, to lead to, to be swept in, by friction, to contaminant, enclosure, either or, a spring, scheduling, motherboard, failure, predictable, eventually, breakdown, inherently, fragile, storage device, impact, transducer, wires, to gold-plated pad, wear, to take it toll, to contain, of damage on, startup, surviving, precision, eliminating the risks, shock performance, tolerance, to utilize, capacity, specified, to run at the higher RLL data rate, sufficient margin, drive’s internal data bus, a master/slave setup, track, significantly, transmission of, to associate, computer bus, undergo, to exit, to survive, controversy, transaction, valued at, appropriate.
Task II.
1) Read texts to comprehend its subject matter and to note the terminological words and word combinations.
2) Look through texts below to copy out the key words and sentences containing the main idea of the texts.
3) Make use of these key words and sentences to compile a short topic to be presented to your classmates at the classroom.
4) After this, try to make common Abstract (orally or in writing).
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Hard Disk Drive
An IBM hard disk drive with the metal cover removed.
The platters are highly reflective. Date Invented: September 13, 1956 Invented By: Reynold Johnson Connects to:
Controller (typically on motherboard) via one of
· PATA (IDE) interface
· SATA interface
· SCSI interface
SAS interface Market Segments:
· Desktop
· Mobile
· Enterprise
· Consumer
Other/MiscellaneousThe inside of a hard disk drive displaying the actuator arm traveling over the top platter
A hard disk (commonly known as a HDD (hard disk drive) or hard drive (HD) and formerly known as a fixed disk) 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 that drives (removable) media, such as a tape drive or (floppy) disk drive, while a hard disk contains fixed (non-removable) media. However, in recent times, the hard disk has become more commonly known as the "hard drive".
Hard disks were originally developed for use with computers. In the 21st century, applications for hard disks 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 hard disks were introduced by Samsung Group and Nokia. The need for large-scale, reliable storage, independent of a particular device, led to the introduction of configurations such as RAID, hardware such as network attached storage (NAS) devices, and systems such as storage area networks (SANs) for efficient access to large volumes of data.
Technology
Hard disks record data by magnetizing a magnetic material in a pattern that represents the data. They read the data back by detecting the magnetization of the material. A typical hard disk 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 fly 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 inside of a hard disk drive with the disk(s) and spindle motor hub removed. To the left of center is the actuator arm. A read-write head is at the end of the arm. In the middle the internal structure of the drive's spindle motor can be seen.
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 hard disks 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 hard disks used the same inductor that was used to read the data as an electromagnet to create this field. 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 are 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.
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Hard disks have a mostly sealed enclosure that protects the disk internals from dust, condensation, and other sources of contamination. The hard disk's read-write heads fly on an air bearing which is a cushion of air only nanometers above the disk surface. The disk surface and the disk's internal environment must therefore be kept immaculate to prevent damage from fingerprints, hair, dust, smoke particles and such, given the sub-microscopic gap between the heads and disk.
Using rigid platters and sealing the unit allows much tighter tolerances than in a floppy disk drive. Consequently, 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 hard disk might store between 160 GB and 750 GB of data (as of local US market by December 2006), rotate at 7,200 to 10,000 revolutions per minute (RPM), and have a sequential media transfer rate of over 80 MB/s. The fastest enterprise hard disks spin at 15,000 RPM, and can achieve sequential media transfer speeds up to and beyond 110 MB/s. Mobile, i.e., Laptop hard disks, which are physically smaller than their desktop and enterprise counterparts, tend to be slower and have less capacity. In the 1990's, most spun at 4,200 RPM. In 2007 a typical mobile hard disk spins at 5,400 RPM and 7,200 RPM models are readily available for a slight price premium.
Capacity
PC hard disk capacity (in GB). The plot is logarithmic, so the fit line corresponds to exponential growth.
The exponential increases in disk space and data access speeds for hard disks has enabled the commercial viability of consumer products that require large storage capacities, such as the Apple iPod digital music player, the TiVo personal video recorder, and web-based email programs, like Google's Gmail. Gmail goes so far as to display a simulation of a real-time counter showing the amount of storage space available to an account as it increases each second.
This is also gradually but significantly altering how programmers think; in many programming tasks there is a time-space tradeoff, so as space becomes cheaper and cheaper relative to CPU cycles the appropriate choice about time versus space changes. For instance in database work it is now common practice to store recomputed views, transitive closures, and the like on disk in order to speed up queries; 20 years ago such profligate use of disk space would have been impractical.
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.
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. However, areal density is determined by two factors: recording density and track density. Track density measures how many tracks that can be packed into one area of space, while recording density measures the amount of data stored in a given physical length unit. Although higher track density can improve seek time, as disk head does not have to move as far to reach scattered data, improvement on transfer rate is not as important as increasing recording density. As of 2006, disk drives include perpendicular recording technology, in the attempt to enhance recording density and throughput.
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The first 3.5" hard disk marketed as able to store 1TB is the Hitachi Deskstar 7K1000. The drive contains five platters at approximately 200 GB each, providing 935.5GB of usable space.
Capacity measurements
Hard disk manufacturers specify disk capacity using the SI definition of the prefixes "mega", "giga", and "tera". This is largely for historical reasons. Disks with multi-million byte capacity have been used since 1956, long before there were standard binary prefixes. The International Electrotechnical Commission (IEC) only standardized binary prefixes in 1999. Many practitioners early on in the computer and semiconductor industries used the prefix kilo to describe 210 (1024) bits, bytes or words because 1024 is close to 1000. Similar usage has been applied to the prefixes mega, giga, tera, and even peta. Often this non-SI conforming usage is noted by a qualifier such as "1 kB = 1,024 bytes" but the qualifier is sometimes omitted, particularly in marketing literature.
Operating systems, such as Microsoft Windows, frequently report capacity using the binary interpretation of the prefixes, which results in a discrepancy between the disk manufacturer's stated capacity and what the system reports. The difference becomes much more noticeable in the multi-gigabyte range. For example, Microsoft's Windows 2000 reports disk capacity both in decimal to 12 or more significant digits and with binary prefixes 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. However utilities provided by Windows define a gigabyte as 230, or 1,073,741,824, bytes, so the reported capacity of the disk will be closer to 28.0 GB. For this reason, many utilities that report capacity have begun to use the aforementioned IEC standard binary prefixes (e.g. KiB, MiB, GiB) since their definitions are unambiguous.
Some people mistakenly attribute the discrepancy in reported and specified capacities to reserved space used for file system and partition accounting information. However, for large (several GiB) filesystems, this data rarely occupies more than a few MiB, and therefore cannot possibly account for the apparent "loss" of tens of GBs.
The capacity of a hard disk 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). However, the cylinder, head, sector values are not accurate for drives using zone bit recording, or address translation. On ATA drives bigger than 8 gibibytes, the values are set to 16383 cylinder, 16 heads, 63 sectors for compatibility with older operating systems.
History
IBM 62PC "Piccolo" HDD, circa 1979 8" disk A 2.5" hard disk for laptops, 2000
For many years, hard disks 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 disks had 8-inch (20 cm) or 14-inch (35 cm) platters, required an equipment rack or a large amount of floor space (especially the large removable-media disks, which were often referred to as "washing machines"), and in many cases needed high-current or even three-phase power hookups due to the large motors they used. Because of this, hard disks were not commonly used with microcomputers until after 1980, when Seagate Technology introduced the ST-506, the first 5.25-inch hard disk, with a capacity of 5 megabytes. In fact, in its factory configuration, the original IBM PC (IBM 5150) was not equipped with a hard disk.
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Most microcomputer hard disks 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, however, and this started a trend toward buying "bare" disks (often by mail order) and installing them directly into a system. Hard disk makers started marketing to end users as well as OEMs, and by the mid-1990s, hard disks had become available on retail store shelves.
While internal disks became the system of choice on PCs, external hard disks remained popular for much longer on the Apple Macintosh and other platforms. The first Apple Macintosh built between 1984 and 1986 had a closed architecture that did not support an external or internal hard drive. In 1986, Apple added a SCSI port on the back, making external expansion easy. External SCSI drives were also popular with older microcomputers such as the Apple II series, and were also used extensively in servers, a usage which is still popular today. The appearance in the late 1990s of high-speed external interfaces such as USB and FireWire has made external disk systems popular among PC users once again, especially for users who move large amounts of data between two or more areas, and most hard disk makers now make their disks available in external cases.
Hard disk characteristics
5.25" MFM 110 MB hard disk (2.5" ATA 6495 MB hard disk, US & UK pennies for comparison)
· Capacity, usually quoted in gigabytes. (older hard disks used to quote their smaller capacities in megabytes)
· Physical size, usually quoted in inches:
o Almost all hard disks today are of either the 3.5" or 2.5" varieties, used in desktops and laptops, respectively. 2.5" disks are usually slower and have less capacity, but use less power and are more tolerant of movement. However, as of early 2007, manufacturers have started selling SATA and SAS 2.5" drives for use in servers and desktops.
o An increasingly common size is the 1.8" ATA-7 LIF form factor used inside digital audio players and subnotebooks, which provide up to 100GB storage capacity at low power consumption and are highly shock-resistant. A previous 1.8" hard disk standard exists, for 2-5GB sized disks that fit directly into PCMCIA or Cardbus expansion slots. From these, the smaller 1" 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" was a de facto form factor led by IBM's Microdrive, but is now generically called 1" due to other manufacturers producing similar products. There is also a 0.85" form factor produced by Toshiba for use in mobile phones and similar applications, including SD/MMC slot compatible hard disks optimized for video storage on 4G handsets.
o The size designations are more nomenclature than descriptive: for example, a 3.5" drive is named for the size of the floppy disk whose drive bay size it was originally designed to occupy; the drive itself is actually wider.
o The physical dimensions of the most common hard drive bays are as follows.
o Number of I/O operations per second:
o Modern disks can perform around 50 random access or 100 Sequential access operations per second.
v Power consumption (especially important in battery-powered laptops).
v audible noise in dBA (although many still report it in bels, not decibels).
v G-shock rating (surprisingly high in modern disks).
v Transfer Rate:
o Inner Zone: from 44.2 MB/s to 74.5 MB/s.
o Outer Zone: from 74.0 MB/s to 111.4 MB/s.
v Random access time: from 5 ms to 15 ms.
Integrity
An IBM hard disk head suspended
above the disk platter.
The hard disk's spindle system relies on air pressure inside the enclosure to support the heads at their proper flying height while the disk is in motion. A hard disk requires a certain range of air pressures in order to operate properly. The connection to the external environment and pressure occurs through a small hole in the enclosure (about 1/2 mm in diameter), usually with a carbon filter on the inside (the breather filter, see below). If the air pressure is too low, there will not be enough lift for the flying head, the head will not be at the proper height, 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 10,000 feet (3,000 m). This does not apply to pressurized enclosures, like an airplane pressurized cabin. Modern disks include temperature sensors and adjust their operation to the operating environment.
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Very high humidity for extended periods can cause accelerated wear of the heads and platters by corrosion. If the disk uses "Contact Start/Stop" (CSS) technology to park its heads on the platters when not operating, increased humidity can also lead to increased stiction (the tendency for the heads to stick to the platter surface). This can cause physical damage to the platter and spindle motor and can also lead to head crash. Breather holes can be seen on all disks — they usually have a warning sticker next to them, informing the user not to cover the holes. The air inside the operating disk 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.
Close-up of a hard disk head suspended above the disk platter together with its mirror image in the smooth surface of the magnetic platter.
Due to the extremely close spacing between the heads and the disk surface, any contamination of the read-write heads or platters can lead to a head crash — a failure of the disk in which the head scrapes across the platter surface, often grinding away the thin magnetic film. For giant magnetoresistive (GMR) heads in particular, a minor head crash from contamination (that does not remove the magnetic surface of the disk) will still result in the head temporarily overheating, due to friction with the disk surface, and can render the data unreadable for a short period until the head temperature stabilizes (so called "thermal asperity," a problem which can partially be dealt with by proper electronic filtering of the read signal). Head crashes can be caused by electronic failure, a sudden power failure, physical shock, wear and tear, corrosion, or poorly manufactured platters and heads. In most desktop and server disks, when powering down, the heads are moved to a landing zone, an area of the platter usually near its inner diameter (ID), where no data is stored. This area is called the CSS (Contact Start/Stop) zone. However, especially in old models, sudden power interruptions or a power supply failure can sometimes result in the device shutting down with the heads in the data zone, which increases the risk of data loss. In fact, it used to be procedure to "park" the hard disk before shutting down your computer. Newer disks are designed such that either a spring (at first) or (more recently) rotational inertia in the platters is used to safely park the heads in the case of unexpected power loss.
The hard disk'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. Modern disk firmware is capable of scheduling reads and writes efficiently on the platter surfaces and remapping sectors of the media which have failed. Also, most major hard disk and motherboard vendors now support self-monitoring, analysis, and reporting technology (S.M.A.R.T.), which attempt to alert users to impending failures.
However, not all failures are predictable. Normal use eventually can lead to a breakdown in the inherently fragile device, which makes it essential for the user to periodically back up the data onto a separate storage device. Failure to do so can lead to the loss of data. While it may be possible to recover lost information, it is normally an extremely costly procedure, and it is not possible to guarantee success in the attempt. A 2007 study published by Google suggested very little correlation between failure rates and either high temperature or activity level. While several S.M.A.R.T. parameters have an impact on failure probability, a large fraction of failed drives do not produce predictive S.M.A.R.T. parameters. S.M.A.R.T. parameters alone may not be useful for predicting individual drive failures.
Landing zones
Microphotograph of a hard disk head. The size of the front face (which is the "trailing face" of the slider) is about 0.3 mm Ч 1.0 mm. The (not visible) bottom face of the slider is about 1.0 mm Ч 1.25 mm (so called "nano" size) and faces the platter. One functional part of the head is the round, orange structure in the middle - the lithographically defined copper coil of the write transducer. Also note the electric connections by wires bonded to gold-plated pads.
Spring tension from the head mounting constantly pushes the heads towards the platter. While the disk is spinning, the heads are supported by an air bearing and experience no physical contact or wear. In CSS drives the sliders carrying the head sensors (often also just called heads) are designed to reliably survive a number of landings and takeoffs from the media surface, though wear and tear on these microscopic components eventually takes its toll. The heads typically land in a "landing zone" that does not contain user data. Most manufacturers design the sliders to survive 50,000 contact cycles before the chance of damage on startup rises above 50%. However, the decay rate is not linear—when a disk is younger and has fewer start-stop cycles, it has a better chance of surviving the next startup than an older, higher-mileage disk (as the head literally drags along the disk's surface until the air bearing is established). For example, the Seagate Barracuda 7200.10 series of desktop hard disks are rated to 50,000 start-stop cycles. This means that no failures attributed to the head-platter interface were seen before at least 50,000 start-stop cycles during testing.
Around 1995 IBM pioneered a technology where a landing zone on the disk is made by a precision laser process (Laser Zone Texture = LZT) producing an array of smooth nanometer-scale "bumps" in a landing zone, thus vastly improving stiction and wear performance. This technology is still largely in use today (2006). In most mobile applications, the heads are lifted off the platters onto plastic "ramps" near the outer disk edge, thus eliminating the risks of wear and stiction altogether and greatly improving non-operating shock performance. All HDD's use one of these two technologies. Each has a list of advantages and drawbacks in terms of loss of storage space, relative difficulty of mechanical tolerance control, cost of implementation, etc.
IBM created a technology for their Thinkpad line of laptop computers called the Active Protection System. When a sudden, sharp movement is detected by the built-in motion sensor in the Thinkpad, internal hard disk heads automatically unload themselves into the parking zone to reduce the risk of any potential data loss or scratches made. Apple later also utilized this technology in their Powerbook, iBook, MacBook Pro, and MacBook line, known as the Sudden Motion Sensor.
Access and interfaces. Hard disk drives are accessed over one of a number of bus types, including ATA (IDE, EIDE), Serial ATA (SATA), SCSI, SAS, and Fibre Channel. Bridge circuitry is sometimes used to connect hard disk drives to busses that they cannot communicate with natively, such as IEEE 1394 and USB.
Back in the days of the ST-506 interface, the data encoding scheme was also important. The first ST-506 disks used Modified Frequency Modulation (MFM) encoding, and transferred data at a rate of 5 megabits per second. Later on, controllers using 2,7 RLL (or just "RLL") encoding increased the transfer rate by fifty percent, to 7.5 megabits per second; it also increased disk capacity by fifty percent.
Many ST-506 interface disk drives were only specified by the manufacturer to run at the lower MFM data rate, while other models (usually more expensive versions of the same basic disk drive) were specified to run at the higher RLL data rate. In some cases, a disk drive had sufficient margin to allow the MFM specified model to run at the faster RLL data rate; however, this was often unreliable and was not recommended. (An RLL-certified disk drive could run on a MFM controller, but with 1/3 less data capacity and speed.)
Enhanced Small Disk Interface (ESDI) also supported multiple data rates (ESDI disks always used 2,7 RLL, but at 10, 15 or 20 megabits per second), but this was usually negotiated automatically by the disk drive and controller; most of the time, however, 15 or 20 megabit ESDI disk drives weren't downward compatible (i.e. a 15 or 20 megabit disk drive wouldn't run on a 10 megabit controller). ESDI disk drives typically also had jumpers to set the number of sectors per track and (in some cases) sector size.
SCSI originally had just one speed, 5 MHz (for a maximum data rate of 5 megabytes per second), but later this was increased dramatically. The SCSI bus speed had no bearing on the disk's internal speed because of buffering between the SCSI bus and the disk drive's internal data bus; however, many early disk drives had very small buffers, and thus had to be reformatted to a different interleave (just like ST-506 disks) when used on slow computers, such as early IBM PC compatibles and early Apple Macintoshes.
ATA disks have typically had no problems with interleave or data rate, due to their controller design, but many early models were incompatible with each other and couldn't run in a master/slave setup (two disks on the same cable). This was mostly remedied by the mid-1990s, when ATA's specification was standardised and the details began to be cleaned up, but still causes problems occasionally (especially with CD-ROM and DVD-ROM disks, and when mixing Ultra DMA and non-UDMA devices).
Serial ATA does away with master/slave setups entirely, placing each disk on its own channel (with its own set of I/O ports) instead.
FireWire/IEEE 1394 and USB(1.0/2.0) hard disks are external units containing generally ATA or SCSI disks with ports on the back allowing very simple and effective expansion and mobility. Most FireWire/IEEE 1394 models are able to daisy-chain in order to continue adding peripherals without requiring additional ports on the computer itself.
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