Parts of Hard Disk

Head Sliders, Arms and Actuator
The hard disk platters are accessed for read and write operations using theread/write heads mounted on the top and bottom surfaces of each platter. Obviously, the read/write heads don't just float in space; they must be held in an exact position relative to the surfaces they are reading, and furthermore, they must be moved from track to track to allow access to the entire surface of the disk. The heads are mounted onto a structure that facilitates this process. Often called the head assembly or actuator assembly (or even the head-actuator assembly), it is comprised of several different parts.
The heads themselves are mounted on head sliders. The sliders are suspended over the surface of the disk at the ends of the head arms. The head arms are all mechanically fused into a single structure that is moved around the surface of the disk by the actuator. (Sort of like "the leg bone's connected to the knee bone", isn't it? :^) ) It would be an understatement to say that these components are neglected; heck, most people don't even know they exist! Yet they play an important role in the function and performance of the drive. In particular, advances in slider, arm and actuator design are critical to improving the seek time of a hard disk; the impact that the actuator has on performance is discussed in this section.

Annotated illustration of a typical PC actuator assembly, showing the major
components. The platters have been removed from the drive to provide a better
view of the actuator arms and heads. There are four sliders but only
one of each pair is visible. The spindle motor is visible at the top right.
This section discusses the sliders, arms and actuator of the modern disk drive, as well as explaining the operation of disk drive servo mechanisms and related technologies.

Head Sliders :
Hard disk read/write heads are too small to be used without attaching them to a larger unit. This is especially true of modern hard disk heads. Each hard disk head is therefore mounted to a special device called a head slider or just sliderfor short. The function of the slider is to physically support the head and hold it in the correct position relative to the platter as the head floats over its surface.
Sliders are given a special shape to allow them to ride precisely over the platter. Usually they are shaped somewhat like a sled; there are two rails or runners on the outside that support the slider at the correct flying height over the surface of the disk, and in the middle the read/write head itself is mounted, possibly on another rail.
As hard disk read/write heads have been shrinking in size, so have the sliders that carry them. The main advantage of using small sliders is that it reduces the weight that must be yanked around the surface of the platters, improving both positioning speed and accuracy. Smaller sliders also have less surface area to potentially contact the surface of the disk.
A graphic illustration of what approximately 15 years' worth of
technological evolution has done to hard disk head sliders.
At left, a slider from a 40 MB 5.25" ferrite-head drive;
at right, the slider from a 3.2 GB, 3.5" MR-head drive.
The hard disk industry has given names to various generations of slidertechnology. When the design was first reduced to 50% of the size of the first hard disk sliders, someone decided to call it the nano-slider, where "nano" is the prefix denoting "one billionth". Of course the name is silly, since the sliders have not shrunk by even a factor of 10. The newest sliders have been shrunk from the "nano" size by about another 50% and are being called pico-sliders, which in this author's opinion is an equally silly name, and for the same reason. :^)
Each slider is mounted onto a head arm to allow it to be moved over the surface of the platter to which it is mated.

Head Arms :
The head arms are thin pieces of metal, usually triangular in shape onto which the head sliders (carrying the read/write heads) are mounted. In a way, the idea here is similar to how the arm of a phonograph is used to move the stylus from the outside of a record to the inside (although of course the similarity ends there). There is one arm per read/write head, and all of them are lined up and mounted to the head actuator to form a single unit. This means that when the actuator moves, all of the heads move together in a synchronized fashion. Heads cannot be individually sent to different track numbers.
The top head arm of a typical recent-design hard disk drive. Note
that the arm is not solid, but rather has a structural triangular shape.
This is done to reduce weight while maintaining rigidity.
The arms themselves are made of a lightweight, thin material, to allow them to be moved rapidly from the inner to outer parts of the drive. Newer designs have replaced solid arms with structural shapes in order to reduce weight andimprove performance. This is the same technique used to reduce weight in the construction of airplane wings, for example. Newer drives achieve faster seek times in part by using faster and smarter actuators and lighter, more rigid head arms, allowing the time to switch between tracks to be reduced.
A recent trend in the hard disk industry has been the reduction in the number of platters in various drive families. Even some "flagship" drives in various families now only have three or even two platters, where four or five was commonplace a year or so ago. One reason for this trend is that having a large number of head arms makes it difficult to make the drive with high enough precision to permit very fast positioning (on random seeks). This is due to increased weight in the actuator assembly from the extra arms, and also problems aligning all the heads. So in essence, this is a tradeoff that some drive manufacturers are making to improve performance at the expense of capacity. With drive densities now at 20 GB per platter and bound to increase, this is an acceptable design decision for most buyers.

Head Actuator :
The actuator is the device used to position the head arms to different tracks on the surface of the platter (actually, to different cylinders, since all head arms are moved as a synchronous unit, so each arm moves to the same track number of its respective surface). The actuator is a very important part of the hard disk, because changing from track to track is the only operation on the hard disk that requires active movement: changing heads is an electronic function, and changing sectors involves waiting for the right sector number to spin around and come under the head (passive movement). Changing tracks means the heads must be shifted, and so making sure this movement can be done quickly and accurately is of paramount importance. This is especially so because physical motion is so slow compared to anything electronic--typically a factor of 1,000 times slower or more.
Head actuators come in two general varieties:
  • Stepper Motors: Originally, hard disk drives used a stepper motor to control the movement of the heads over the surface of the platters. A regular motor turns in a rotary fashion continuously; it can stop at any point in its rotation as it spins around, kind of like the second hand on a wind-up wristwatch. A stepper motor can only stop at predefined "steps" as it turns around, much the way the second hand turns on an electronic, quartz wristwatch. A hard drive using a stepper motor for an actuator attaches the arms to the motor, and each time the motor steps one position clockwise or counterclockwise, the arms move in or out one position. Each position defines a track on the surface of the disk. Stepper motors are also commonly used for both turning the spindle and positioning the head on floppy disk drives. If you have a floppy drive, find one of its motors and turn it slowly with your hand; you will feel the discrete step-wise nature of its motion.
A stepper motor actuator. The motor moves in steps, which you can feel if
you move the motor shaft by hand. The shaft has two thin strips of metal
wrapped around it, which are connected to a pivot that is rigidly attached
to the actuator arms. As the motor shaft turns, one half of this "split band"
coils onto the shaft and the other half uncoils. When the motor turns in the
opposite direction the process reverses. As this occurs the pivot moves
and in doing so, moves the actuator arms and the hard disk heads.
  • Voice Coils: The actuator in a modern hard disk uses a device called avoice coil to move the head arms in and out over the surface of the platters, and a closed-loop feedback system called a servo system to dynamically position the heads directly over the data tracks. The voice coil works using electromagnetic attraction and repulsion. A coil is wrapped around a metal protrusion on the end of the set of head arms. This is mounted within an assembly containing a strong permanent magnet. When current is fed to the coil, an electromagnetic field is generated that causes the heads to move in one direction or the other based on attraction or repulsion relative to the permanent magnet. By controlling the current, the heads can be told to move in or out much more precisely than using a stepper motor. The name "voice coil" comes from the resemblance of this technology to that used to drive audio speakers, which are also basically electromagnets. All PC hard disk voice coil actuators are rotary, meaning that the actuator changes position by rotating on an axis.
A partially-disassembled voice coil actuator. The magnet assembly has
been unscrewed from its mounting and pulled to the left to expose the
coil. The magnet assembly consists of two metal plates (top one  easily
visible above, and part of the bottom one visible.) The magnet itself is
mounted on the underside of the top plate, and spacers used between
the plates to create the gap for the coil assembly. Being non-ferrous the
coil moves freely between the plates, rotating the actuator on its axis
as its magnetic polarity is changed. (Incidentally, the magnet is strong
enough that after removing the spacers between the plates, the bottom plate
got "stuck" on the magnet and required considerable effort to remove!)
The primary distinction between the two designs is that the stepper motor is anabsolute positioning system, while the voice coil is a relative positioning system. Commands given to a stepper motor actuator are generally of the form "Go in this direction to position A, where you'll find item B". Commands to a voice coil actuator are of the form "Go in this direction until you find item B". Consider this analogy. In your backyard you have buried a "secret treasure" and want to tell a friend where to find it. When you buried it, you walked down a path 139 paces to the fourth oak tree, and buried it at the edge of the path. The stepper motor analog would be to tell your friend to walk 139 paces down the path, and start digging. The voice coil analog would be to tell him to look for the fourth oak tree and dig there. Obviously, using the "139 paces" method, your friend has a problem: his paces aren't likely to be the same length as yours. In fact, even if you yourself walked out 139 paces twice, you'd probably end up in very different spots, since a "pace" isn't an accurate or repeatable measure. On the other hand, the fourth oak tree will always be the fourth oak tree (barring disastrous chain-saw activity :^) ).
Now hard disks of course don't have to use inaccurate measures like "paces", and it's always the same stepper motor accessing the disk, not a "friend", so why is saying "track #139" a big problem? For starters, motors change their characteristics over time, and after a year or two position #139 might not be where it was when the drive was first formatted. However, they have an even more serious problem: disk components (the platters and the head arms themselves especially) expand and contract with heat. Even if a stepper motor was perfect, it could not properly account for the fact that the disks are changing in size, and therefore, the tracks are literally moving around. If you consider our backyard analogy and think about what it would be like if the oak tree moved a few feet closer to or further from the house based on the day's temperature, you start to realize how inadequate absolute positioning of this form can be.
A stepper motor has no way to compensate for expansion or contraction of the disk: all it can do is go to where "track #139" is supposed to be, and hope it finds it there! If it doesn't find it because the motor and the disk have become out of sync, errors and data loss result. This is why older disks were so sensitive to temperature, and normally had to be low-level formattedperiodically to make sure the tracks lined up with the heads properly. This is also why many drives would fail when first powered up after a weekend, but would work properly after the drive had been allowed to warm up.
The shortcomings of stepper motors were unfortunate but acceptable with old hard disks, because of their relatively low track density. To compensate, tracks could be written fairly wide so that the head would find them even if it was a bit misaligned. The first PC hard disks in 1982 had a track density of only two or three hundred tracks per inch (TPI). Even In 1986, the year Conner Peripherals introduced the first voice coil PC hard disk, density had increased to only about 1,000 TPI. Stepper motors are still used to drive floppy disks, for example, because the accuracy demands for floppies are much lower: a 1.44 MB floppy disk has a track density of 135 tracks per inch. In contrast, today's hard disks have densities as high as 30,000 tracks per inch. With data packed this densely, tracks are extremely thin, and a stepper motor lacks the accuracy and stability necessary for proper operation.
All modern hard disks use voice coil actuators. The voice coil actuator is not only far more adaptable and insensitive to thermal issues, it is much faster and more reliable than a stepper motor. The actuator's positioning is dynamic and is based on feedback from examining the actual position of the tracks. This closed-loop feedback system is also sometimes called a servo motor or servo positioning system and is commonly used in thousands of differentapplications where precise positioning is important. There are several different ways that the servo positioning system is implemented in PCs; the servo's operation is discussed in its own section.


Hard Disk

Hard Disk Drives
The hard disk drive in your system is the "data center" of the PC. It is here that all of your programs and data are stored between the occasions that you use the computer. Your hard disk (or disks) are the most important of the various types of permanent storage used in PCs (the others being floppy disks and other storage media such as CD-ROMs, tapes, removable drives, etc.) The hard disk differs from the others primarily in three ways: size (usually larger), speed (usually faster) and permanence (usually fixed in thePC and not removable).
Hard disk drives are almost as amazing as microprocessors in terms of thetechnology they use and how much progress they have made in terms of capacity, speed, and price in the last 20 years. The first PC hard disks had a capacity of 10 megabytes and a cost of over $100 per MB. Modern hard disks have capacities approaching 100 gigabytes and a cost of less than 1 cent per MB! This represents an improvement of 1,000,000% in just under 20 years, or around 67% cumulative improvement per year. At the same time, the speed of the hard disk and its interfaces have increased dramatically as well.

Top view of a 36 GB, 10,000 RPM, IBM SCSI
server hard disk, with its top cover removed.
Note the height of the drive and the 10 stacked platters.
(The IBM Ultrastar 36ZX.)
Original image © IBM Corporation
Image used with permission.
Your hard disk plays a significant role in the following important aspects of your computer system:
  • Performance: The hard disk plays a very important role in overall system performance, probably more than most people recognize (though that is changing now as hard drives get more of the attention they deserve). The speed at which the PC boots up and programs load is directly related to hard disk speed. The hard disk's performance is also critical when multitasking is being used or when processing large amounts of data such as graphics work, editing sound and video, or working with databases.
  • Storage Capacity: This is kind of obvious, but a bigger hard disk lets you store more programs and data.
  • Software Support: Newer software needs more space and faster hard disks to load it efficiently. It's easy to remember when 1 GB was a lot of disk space; heck, it's even easy to remember when 100 MB was a lot of disk space! Now a PC with even 1 GB is considered by many to be "crippled", since it can barely hold modern (inflated)operating system files and a complement of standard business software.
  • Reliability: One way to assess the importance of an item of hardware is to consider how much grief is caused if it fails. By this standard, the hard disk is the most important component by a long shot. As I often say, hardware can be replaced, but data cannot. A good quality hard disk, combined with smart maintenance and backup habits, can help ensure that the nightmare of data loss doesn't become part of your life.
This chapter takes a very detailed look at hard disks and how they work. This includes a full dissection of the internal components in the drive, a look at how data is formatted and stored, a discussion of performance issues, and a full analysis of the two main interfaces used to connect hard disks to the rest of the PC. A discussion is also included about the many confusing issues regarding hard disks and BIOS versions, and support for the newer and larger hard disks currently on the market. Finally, a full description is given of logical hard disk structures and the functioning of the FAT and NTFS file systems, by far the most popular currently used by PCs.

Keyboard Shortcuts

General keyboard shortcuts

  • CTRL+C (Copy)
  • CTRL+X (Cut)
  • CTRL+V (Paste)
  • CTRL+Z (Undo)
  • DELETE (Delete)
  • SHIFT+DELETE (Delete the selected item permanently without placing the item in the Recycle Bin)
  • CTRL while dragging an item (Copy the selected item)
  • CTRL+SHIFT while dragging an item (Create a shortcut to the selected item)
  • F2 key (Rename the selected item)
  • CTRL+RIGHT ARROW (Move the insertion point to the beginning of the next word)
  • CTRL+LEFT ARROW (Move the insertion point to the beginning of the previous word)
  • CTRL+DOWN ARROW (Move the insertion point to the beginning of the next paragraph)
  • CTRL+UP ARROW (Move the insertion point to the beginning of the previous paragraph)
  • CTRL+SHIFT with any of the arrow keys (Highlight a block of text)
  • SHIFT with any of the arrow keys (Select more than one item in a window or on the desktop, or select text in a document)
  • CTRL+A (Select all)
  • F3 key (Search for a file or a folder)
  • ALT+ENTER (View the properties for the selected item)
  • ALT+F4 (Close the active item, or quit the active program)
  • ALT+ENTER (Display the properties of the selected object)
  • ALT+SPACEBAR (Open the shortcut menu for the active window)
  • CTRL+F4 (Close the active document in programs that enable you to have multiple documents open simultaneously)
  • ALT+TAB (Switch between the open items)
  • ALT+ESC (Cycle through items in the order that they had been opened)
  • F6 key (Cycle through the screen elements in a window or on the desktop)
  • F4 key (Display the Address bar list in My Computer or Windows Explorer)
  • SHIFT+F10 (Display the shortcut menu for the selected item)
  • ALT+SPACEBAR (Display the System menu for the active window)
  • CTRL+ESC (Display the Start menu)
  • ALT+Underlined letter in a menu name (Display the corresponding menu)
  • Underlined letter in a command name on an open menu (Perform the corresponding command)
  • F10 key (Activate the menu bar in the active program)
  • RIGHT ARROW (Open the next menu to the right, or open a submenu)
  • LEFT ARROW (Open the next menu to the left, or close a submenu)
  • F5 key (Update the active window)
  • BACKSPACE (View the folder one level up in My Computer or Windows Explorer)
  • ESC (Cancel the current task)
  • SHIFT when you insert a CD-ROM into the CD-ROM drive (Prevent the CD-ROM from automatically playing)
  • CTRL+SHIFT+ESC (Open Task Manager)

Dialog box keyboard shortcuts

If you press SHIFT+F8 in extended selection list boxes, you enable extended selection mode. In this mode, you can use an arrow key to move a cursor without changing the selection. You can press CTRL+SPACEBAR or SHIFT+SPACEBAR to adjust the selection. To cancel extended selection mode, press SHIFT+F8 again. Extended selection mode cancels itself when you move the focus to another control.
  • CTRL+TAB (Move forward through the tabs)
  • CTRL+SHIFT+TAB (Move backward through the tabs)
  • TAB (Move forward through the options)
  • SHIFT+TAB (Move backward through the options)
  • ALT+Underlined letter (Perform the corresponding command or select the corresponding option)
  • ENTER (Perform the command for the active option or button)
  • SPACEBAR (Select or clear the check box if the active option is a check box)
  • Arrow keys (Select a button if the active option is a group of option buttons)
  • F1 key (Display Help)
  • F4 key (Display the items in the active list)
  • BACKSPACE (Open a folder one level up if a folder is selected in the Save As or Opendialog box)

Microsoft natural keyboard shortcuts

  • Windows Logo (Display or hide the Start menu)
  • Windows Logo+BREAK (Display the System Properties dialog box)
  • Windows Logo+D (Display the desktop)
  • Windows Logo+M (Minimize all of the windows)
  • Windows Logo+SHIFT+M (Restore the minimized windows)
  • Windows Logo+E (Open My Computer)
  • Windows Logo+F (Search for a file or a folder)
  • CTRL+Windows Logo+F (Search for computers)
  • Windows Logo+F1 (Display Windows Help)
  • Windows Logo+ L (Lock the keyboard)
  • Windows Logo+R (Open the Run dialog box)
  • Windows Logo+U (Open Utility Manager)

Accessibility keyboard shortcuts

  • Right SHIFT for eight seconds (Switch FilterKeys either on or off)
  • Left ALT+left SHIFT+PRINT SCREEN (Switch High Contrast either on or off)
  • Left ALT+left SHIFT+NUM LOCK (Switch the MouseKeys either on or off)
  • SHIFT five times (Switch the StickyKeys either on or off)
  • NUM LOCK for five seconds (Switch the ToggleKeys either on or off)
  • Windows Logo +U (Open Utility Manager)

Windows Explorer keyboard shortcuts

  • END (Display the bottom of the active window)
  • HOME (Display the top of the active window)
  • NUM LOCK+Asterisk sign (*) (Display all of the subfolders that are under the selected folder)
  • NUM LOCK+Plus sign (+) (Display the contents of the selected folder)
  • NUM LOCK+Minus sign (-) (Collapse the selected folder)
  • LEFT ARROW (Collapse the current selection if it is expanded, or select the parent folder)
  • RIGHT ARROW (Display the current selection if it is collapsed, or select the first subfolder)

Shortcut keys for Character Map

After you double-click a character on the grid of characters, you can move through the grid by using the keyboard shortcuts:
  • RIGHT ARROW (Move to the right or to the beginning of the next line)
  • LEFT ARROW (Move to the left or to the end of the previous line)
  • UP ARROW (Move up one row)
  • DOWN ARROW (Move down one row)
  • PAGE UP (Move up one screen at a time)
  • PAGE DOWN (Move down one screen at a time)
  • HOME (Move to the beginning of the line)
  • END (Move to the end of the line)
  • CTRL+HOME (Move to the first character)
  • CTRL+END (Move to the last character)
  • SPACEBAR (Switch between Enlarged and Normal mode when a character is selected)

Microsoft Management Console (MMC) main window keyboard shortcuts

  • CTRL+O (Open a saved console)
  • CTRL+N (Open a new console)
  • CTRL+S (Save the open console)
  • CTRL+M (Add or remove a console item)
  • CTRL+W (Open a new window)
  • F5 key (Update the content of all console windows)
  • ALT+SPACEBAR (Display the MMC window menu)
  • ALT+F4 (Close the console)
  • ALT+A (Display the Action menu)
  • ALT+V (Display the View menu)
  • ALT+F (Display the File menu)
  • ALT+O (Display the Favorites menu)

MMC console window keyboard shortcuts

  • CTRL+P (Print the current page or active pane)
  • ALT+Minus sign (-) (Display the window menu for the active console window)
  • SHIFT+F10 (Display the Action shortcut menu for the selected item)
  • F1 key (Open the Help topic, if any, for the selected item)
  • F5 key (Update the content of all console windows)
  • CTRL+F10 (Maximize the active console window)
  • CTRL+F5 (Restore the active console window)
  • ALT+ENTER (Display the Properties dialog box, if any, for the selected item)
  • F2 key (Rename the selected item)
  • CTRL+F4 (Close the active console window. When a console has only one console window, this shortcut closes the console)

Remote desktop connection navigation

  • CTRL+ALT+END (Open the Microsoft Windows NT Security dialog box)
  • ALT+PAGE UP (Switch between programs from left to right)
  • ALT+PAGE DOWN (Switch between programs from right to left)
  • ALT+INSERT (Cycle through the programs in most recently used order)
  • ALT+HOME (Display the Start menu)
  • CTRL+ALT+BREAK (Switch the client computer between a window and a full screen)
  • ALT+DELETE (Display the Windows menu)
  • CTRL+ALT+Minus sign (-) (Place a snapshot of the entire client window area on the Terminal server clipboard and provide the same functionality as pressing ALT+PRINT SCREEN on a local computer.)
  • CTRL+ALT+Plus sign (+) (Place a snapshot of the active window in the client on the Terminal server clipboard and provide the same functionality as pressing PRINT SCREEN on a local computer.)

Microsoft Internet Explorer navigation

  • CTRL+B (Open the Organize Favorites dialog box)
  • CTRL+E (Open the Search bar)
  • CTRL+F (Start the Find utility)
  • CTRL+H (Open the History bar)
  • CTRL+I (Open the Favorites bar)
  • CTRL+L (Open the Open dialog box)
  • CTRL+N (Start another instance of the browser with the same Web address)
  • CTRL+O (Open the Open dialog box, the same as CTRL+L)
  • CTRL+P (Open the Print dialog box)
  • CTRL+R (Update the current Web page)
  • CTRL+W (Close the current window)


Flexible Keboard / silicon keyobard

Flexible Keboard / silicon keyboard : 
Latest Flexible Keboard / silicon keyobard / soft keyboard / keyobard

Product Description 
- Waterightness: It can be used for a damp environment. It can be nornally used when beverage or ohter liquids spilled.
-Acid and Alkaline-proof: The keyboard can be used safely in acid or alkaline environment.
-High dustproof: The keyboard can be used safely in dust or fog.
-Carriying convenience: Because the keyboard can be rolled up, it can save lots of spaces when carrying.
-Silent: The keyboard is soft without any sound while tying.
-Compatibility IBM AT,Windows98/2000/XP/ Vista
-Communication USB, PS/2 COMBO(USB+PS/2) port
-Size (mm)495(L)x138(W)x12(H)
-Layout109 keys
-Keys High 5.5mm
-Total travel2mm±0.4
-Keyboard N.W.320g
-Keys Life> 5,000,000 times
-Electronic Data+5V DC@250Ma
-Operating temperature -30° to 80°C
-Protection Level IP 67
-Keyboard Color Random color or assigns PANTONE number
-Approvals CE & FCC & ROHS


In computing, a keyboard is an input device, partially modeled after the typewriter keyboard, which uses an arrangement of buttons or keys, to act as mechanical levers or electronic switches. A keyboard typically has characters engraved or printed on the keys and each press of a key typically corresponds to a single written symbol. However, to produce some symbols requires pressing and holding several keys simultaneously or in sequence. While most keyboard keys produce letters, numbers or signs (characters), other keys or simultaneous key presses can produce actions or computer commands.

In normal usage, the keyboard is used to type text and numbers into a word processor, text editor or other program. In a modern computer, the interpretation of key presses is generally left to the software. A computer keyboard distinguishes each physical key from every other and reports all key presses to the controlling software. Keyboards are also used for computer gaming, either with regular keyboards or by using keyboards with special gaming features, which can expedite frequently used keystroke combinations. A keyboard is also used to give commands to the operating system of a computer, such as Windows' Control-Alt-Delete combination, which brings up a task window or shuts down the machine.

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