HARD DISKA hard disk drive (HDD), commonly referred to as a hard drive or hard disk,[1] 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.[2]
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.
Platter 
An aluminum, glass, or ceramic disk that is coated in a magnetic media that is located within a hard disk drive and used to permanently store all your computer's data. When the computer is turned on, these platters will begin to rotate at so many rotations per minute (RPM). This rate varies depending upon the model of hard drive you have; an example of how fast a hard drive may spin is 7200 RPM. As the disk platters are rotating, the read/write head accesses information on one of the platters. It is not uncommon for a computer hard disk drive to have multiple platters. To help store and retrieve the data from the platter, data is stored in tracks, sectors and cylinders on each platter.
An aluminum, glass, or ceramic disk that is coated in a magnetic media that is located within a hard disk drive and used to permanently store all your computer's data. When the computer is turned on, these platters will begin to rotate at so many rotations per minute (RPM). This rate varies depending upon the model of hard drive you have; an example of how fast a hard drive may spin is 7200 RPM. As the disk platters are rotating, the read/write head accesses information on one of the platters. It is not uncommon for a computer hard disk drive to have multiple platters. To help store and retrieve the data from the platter, data is stored in tracks, sectors and cylinders on each platter.
Spindle
The spindle motor, also sometimes called the spindle shaft, is responsible for turning the hard disk platters, allowing the hard drive to operate. The spindle motor is sort of a "work horse" of the hard disk. It's not flashy, but it must provide stable, reliable and consistent turning power for thousands of hours of often continuous use, to allow the hard disk to function properly. In fact, many drive failures are actually failures with the spindle motor, not the data storage systems.
A hard disk spindle motor, stripped of its platters and other components, and detachedfrom the drive's base casting. You can see that it attaches with three screws around itsperimeter. The shiny metal is the shaft, which rotates; the dull metal is the base of the motor.The six small screw holes on the top of the shaft are for securing the platters. You can also seea large screw hole in the center top of the shaft, which is used to attach the top cover to thespindle shaft for added stability. the four wire connector attaches to the hard disk logic board.
Hard Disk Read/Write HeadsThe read/write heads of the hard disk are the interface between the magnetic physical media on which the data is stored and the electronic components that make up the rest of the hard disk (and the PC). The heads do the work of converting bits to magnetic pulses and storing them on the platters, and then reversing the process when the data needs to be read back.
Read/write heads are an extremely critical component in determining the overall performance of the hard disk, since they play such an important role in the storage and retrieval of data. They are usually one of the more expensive parts of the hard disk, and to enable areal densities and disk spin speeds to increase, they have had to evolve from rather humble, clumsy beginnings to being very advanced and complicated technology. New head technologies are often the triggering point to increasing the speed and size of modern hard disks.
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.
The Mounting HoleRTM and RTHM mounting-hole cable ties are recognized under the Component Program of Underwriters Laboratories Inc. for use at temperatures not exceeding 85° C (185° F). File No. E76766(N). The basic and modified Type 66 nylons used in All-States RTM and RTHM Series mounting cable ties meet UL94V-2 Flammability Classification. Fire-retardant Type 66 nylon meets UL 94V-0. All RTM and RTHM Series cable ties are manufactured to the same Mil Spec quality standards required by MS-3367.
ribbon cableribbon cable: 1. Any cable constructed as a ribbon with parallel elements. 2. A fiber optic cable in which the optical fibers are held in grooves and laminated within a flat semirigid strip of material, such as plastic, that positions, holds, and protects them. Note: Ribbon cables may be stacked to produce fiber optic cables with large numbers of fibers. Buffers, strength members, fillers, and jacketing are usually added to produce the final cable.
Seal
Seal used in the case of a computer hard drive disk kit.The stainless steel carrier eliminates a difficult assembly step by making the small rubber cross section rigid. Butyl offers the lowest permeation rate of all elastomersBase Casting and Top Cover
The entire hard disk is mounted into a physical enclosure designed to protect it and also keep its internal environment separated from the outside air. This is necessary because of the requirement of keeping the internal environment free of dust and other contamination that could get between the read/write heads and the platters over which they float, and possibly lead to head crashes.The bottom of the disk is often called the base casting, the name coming from the manufacturing process used to create the single piece of aluminum from which it is normally made. The drive mechanics are placed into the base casting, and another piece of usually aluminum is placed on top to enclose the heads and platters. A rubber gasket is placed between the base and cover to ensure a tight seal. On some drives, a metallic tape seal is applied around the perimeter of the drive to fully enclose the drive. The exact shape of the base and cover can vary significantly from drive to drive. Some models have the base flat and the cover like a bowl that goes over the contents; some are the opposite way.
Motherboard The main circuit board of a microcomputer. The motherboard contains the connectors for attaching additional boards. Typically, the motherboard contains the CPU, BIOS, memory, mass storage interfaces, serial and parallel ports, expansion slots, and all the controllers required to control standard peripheral devices, such as the display screen, keyboard, and disk drive. Collectively, all these chips that reside on the motherboard are known as the motherboard's chipset.
On most PCs, it is possible to add memory chips directly to the motherboard. You may also be able to upgrade to a faster PC by replacing the CPU chip. To add additional core features, you may need to replace the motherboard entirely.
Motherboard is sometimes abbreviated as mobo.
On most PCs, it is possible to add memory chips directly to the motherboard. You may also be able to upgrade to a faster PC by replacing the CPU chip. To add additional core features, you may need to replace the motherboard entirely.
Motherboard is sometimes abbreviated as mobo.
NorthbridgeAn integrated circuit (generally Intel or VIA) that is responsible for the communications between the CPU interface, AGP, PCI and the memory. The northbridge gets its name for commonly being North of the PCI bus. Below is a graphic illustration of the ASUS P5AD2-E motherboard and some basic explanations of each of the major portions of the motherboard, including the northbridge. As shown in the below picture, it's common for the northbridge and southbridge to have a heatsink; in addition, the northbridge is usually slightly larger than the southbridge.
GeekStuff4U has a diminutive Compact Flash card reader that can be fitted directly onto the 40-pin IDE port of a PC. You might wonder what is the point of this entire exercise - well, for starters, this configuration allows you to run both Linux as well as another lightweight OS (for example, Windows CE) on your computer. Imagine carrying an entire operating system on a Compact Flash card. It is just one of those things that keep you secure when you go to bed at night knowing that you have the ability to dual-boot via a CF card when the need arises, just like how driving a Ferrari through a traffic jam feels like. 
Processor Sockets and SlotsThe purpose of the motherboard socket originally was just to provide a place to insert the processor into the motherboard. As such, it was no different than the sockets that were put on the board for most of the other PC components. However, over the last few years Intel, the primary maker of processors in the PC world, has defined several interface standards for PC motherboards. These are standardized socket and slot specifications to be used with various processors that are designed to use these standard sockets.
What is significant about the creation of these standards is that Intel's two main competitors, AMD and Cyrix, have been able to use these standards as well in their quest for compatibility with Intel. While packages and sockets/slots do change over time, the presence of standards allows for better implementations by motherboard makers, who can make boards that hopefully support future processors more easily than if each board had to be tailored to a specific chip.
Accelerated Graphics Port (AGP)The need for increased bandwidth between the main processor and the video subsystem originally lead to the development of the local I/O bus on the PCs, starting with the VESA local bus and eventually leading to the popular PCI bus. This trend continues, with the need for video bandwidth now starting to push up against the limits of even the PCI bus.
Much as was the case with the ISA bus before it, traffic on the PCI bus is starting to become heavy on high-end PCs, with video, hard disk and peripheral data all competing for the same I/O bandwidth. To combat the eventual saturation of the PCI bus with video information, a new interface has been pioneered by Intel, designed specifically for the video subsystem. It is called the Accelerated Graphics Port or AGP.
AGP was developed in response to the trend towards greater and greater performance requirements for video. As software evolves and computer use continues into previously unexplored areas such as 3D acceleration and full-motion video playback, both the processor and the video chipset need to process more and more information. The PCI bus is reaching its performance limits in these applications, especially with hard disks and other peripherals also in there fighting for the same bandwidth.
Another issue has been the increasing demands for video memory. As 3D computing becomes more mainstream, much larger amounts of memory become required, not just for the screen image but also for doing the 3D calculations. This traditionally has meant putting more memory on the video card for doing this work. There are two problems with this:
Cost: Video card memory is very expensive compared to regular system RAM.
Limited Size: The amount of memory on the video card is limited: if you decide to put 6 MB on the card and you need 4 MB for the frame buffer, you have 2 MB left over for processing work and that's it (unless you do a hardware upgrade). It's not easy to expand this memory, and you can't use it for anything else if you don't need it for video processing.
AGP gets around these problems by allowing the video processor to access the main system memory for doing its calculations. This is more efficient because this memory can be shared dynamically between the system processor and the video processor, depending on the needs of the system.
The idea behind AGP is simple: create a faster, dedicated interface between the video chipset and the system processor. The interface is only between these two devices; this has three major advantages: it makes it easier to implement the port, makes it easier to increase AGP in speed, and makes it possible to put enhancements into the design that are specific to video.
AGP is considered a port, and not a bus, because it only involves two devices (the processor and video card) and is not expandable. One of the great advantages of AGP is that it isolates the video subsystem from the rest of the PC so there isn't nearly as much contention over I/O bandwidth as there is with PCI. With the video card removed from the PCI bus, other PCI devices will also benefit from improved bandwidth.
AGP is a new technology and was just introduced to the market in the third quarter of 1997. The first support for this new technology will be from Intel's 440LX Pentium II chipset. More information on AGP will be forthcoming as it becomes more mainstream and is seen more in the general computing market. Interestingly, one of Intel's goals with AGP was supposed to be to make high-end video more affordable without requiring sophisticated 3D video cards. If this is the case, it really makes me wonder why they are only making AGP available for their high-end, very expensive Pentium II processor line. :^) Originally, AGP was rumored to be a feature on the 430TX Pentium socket 7 chipset, but it did not materialize. Via and other companies are carrying the flag for future socket 7 chipset development now that Intel has dropped it, and several non-Intel AGP-capable chipsets will be entering the market in 1998.
PCI
Short for Peripheral Component Interconnect, a local bus standard developed by Intel Corporation. Most modern PCs include a PCI bus in addition to a more general ISA expansion bus. PCI is also used on newer versions of the Macintosh computer.PCI is a 64-bit bus, though it is usually implemented as a 32-bit bus. It can run at clock speeds of 33 or 66 MHz. At 32 bits and 33 MHz, it yields a throughput rate of 133 MBps. Also see PCI-X and PCI Express.
Although it was developed by Intel, PCI is not tied to any particular family of microprocessors.
SERIAL ATA - A specification for consumer hard drive connections that boosts the data transfer rate up to 150MB/second. In addition, it changes IDE/ATA from a parallel interface requiring 40 separate wires to connect components to a serial interface requiring only 6 wires. 2x and 4x versions of Serial ATA double and quadruple the speed of Serial ATA
SouthbridgeSouthbridge is an Intel chipset that manages the basic forms of input/output (I/O) such as Universal Serial Bus (USB), serial, audio, Integrated Drive Electronics (IDE), and Industry Standard Architecture (ISA) I/O in a computer. Southbridge is one of two chipsets that are collectively called Northbridge/Southbridge. Northbridge controls the processor, memory, Peripheral Component Interconnect (PCI) bus, Level 2 cache, and all Accelerated Graphics Port (AGP) activities. Unlike Northbridge, Southbridge consists of one chip, which sits on Northbridge's PCI bus.
The Intel Hub Architecture (IHA) has replaced the Northbridge/Southbridge chipset. The IHA chipset has two parts also, the Graphics and AGP Memory Controller Hub (GMCH) and the I/O Controller Hub (ICH). The IHA architecture is used in Intel's 800 series chipsets, which is the first chipset architecture to move away from the Northbridge/Southbridge design.
The Intel Hub Architecture (IHA) has replaced the Northbridge/Southbridge chipset. The IHA chipset has two parts also, the Graphics and AGP Memory Controller Hub (GMCH) and the I/O Controller Hub (ICH). The IHA architecture is used in Intel's 800 series chipsets, which is the first chipset architecture to move away from the Northbridge/Southbridge design.
Computer Memoryan electronic memory device: "a memory and the CPU form the central part of a computer to which peripherals are attached"
DRAM MEMORY
Often referred to as main memory RAM is the acronym for Random Access Memory. It is a type of computer memory that can, as its name implies, be accessed randomly. That is, any byte of memory can be accessed without touching the preceding bytes. RAM is the "working memory" storage area within the computer. All data on the computer is stored on the hard drive, but in order for the CPU to work with the data during normal operations, the data the computer uses and works with is read into the working memory, which is the RAM chips.
There are two different types of RAM; DRAM (Dynamic Random Access Memory) and SRAM (Static Random Access Memory). The two types differ in the technology they use to hold data, with DRAM being the more common type. In terms of speed, SRAM is faster. DRAM needs to be refreshed thousands of times per second while SRAM does not need to be refreshed, which is what makes it faster. DRAM supports access times of about 60 nanoseconds, SRAM can give access times as low as 10 nanoseconds.
Despite SRAM being faster, it is not as commonly used as DRAM because it is so much more expensive. Both types of RAM are volatile, meaning that they lose their contents when the power is turned off.
This reference will provide general information on the two types of RAM and provide an overview on the common modules of each type. As DRAM is the main system memory used in home and office PCs, being cheaper and more common than SRAM, we will focus on DRAM.
There are two different types of RAM; DRAM (Dynamic Random Access Memory) and SRAM (Static Random Access Memory). The two types differ in the technology they use to hold data, with DRAM being the more common type. In terms of speed, SRAM is faster. DRAM needs to be refreshed thousands of times per second while SRAM does not need to be refreshed, which is what makes it faster. DRAM supports access times of about 60 nanoseconds, SRAM can give access times as low as 10 nanoseconds.
Despite SRAM being faster, it is not as commonly used as DRAM because it is so much more expensive. Both types of RAM are volatile, meaning that they lose their contents when the power is turned off.
This reference will provide general information on the two types of RAM and provide an overview on the common modules of each type. As DRAM is the main system memory used in home and office PCs, being cheaper and more common than SRAM, we will focus on DRAM.
System UnitThe main part of a personal computer. The system unit includes the chassis, microprocessor, main memory, bus, and ports, but does not include the keyboard or monitor, or any peripheral devices.
A system unit is sometimes called a box or main unit
A system unit is sometimes called a box or main unit
MonitorSoftware or hardware that is used to scrutinize and to display, record, supervise, control, or verify the operations of a system. Note: Possible uses of monitors are to indicate significant departures from the norm, or to determine levels of utilization of particular functional units. A device used for the real-time temporary display of computer output data. Note: Monitors usually use cathode-ray-tube or liquid-crystal technology. Synonyms CRT, video display terminal, video display unit, visual display unit.
KeyboardThe set of typewriter-like keys that enables you to enter data into a computer. Computer keyboards are similar to electric-typewriter keyboards but contain additional keys. The keys on computer keyboards are often classified as follows:
alphanumeric keys -- letters and numbers
punctuation keys -- comma, period, semicolon, and so on.
special keys -- function keys, control keys, arrow keys, Caps Lock key, and so on.
The standard layout of letters, numbers, and punctuation is known as a QWERTY keyboard because the first six keys on the top row of letters spell QWERTY. The QWERTY keyboard was designed in the 1800s for mechanical typewriters and was actually designed to slow typists down to avoid jamming the keys. Another keyboard design, which has letters positioned for speed typing, is the Dvorak keyboard.
There is no standard computer keyboard, although many manufacturers imitate the keyboards of PCs. There are actually three different PC keyboards: the original PC keyboard, with 84 keys; the AT keyboard, also with 84 keys; and the enhanced keyboard, with 101 keys. The three differ somewhat in the placement of function keys, the Control key, the Return key, and the Shift keys.
In addition to these keys, IBM keyboards contain the following keys: Page Up, Page Down, Home, End, Insert, Pause, Num Lock, Scroll Lock, Break, Caps Lock, Print Screen.
There are several different types of keyboards for the Apple Macintosh. All of them are called ADB keyboards because they connect to the Apple Desktop bus (ADB). The two main varieties of Macintosh keyboards are the standard keyboard and the extended keyboard, which has 15 additional special-function keys.
alphanumeric keys -- letters and numbers
punctuation keys -- comma, period, semicolon, and so on.
special keys -- function keys, control keys, arrow keys, Caps Lock key, and so on.
The standard layout of letters, numbers, and punctuation is known as a QWERTY keyboard because the first six keys on the top row of letters spell QWERTY. The QWERTY keyboard was designed in the 1800s for mechanical typewriters and was actually designed to slow typists down to avoid jamming the keys. Another keyboard design, which has letters positioned for speed typing, is the Dvorak keyboard.
There is no standard computer keyboard, although many manufacturers imitate the keyboards of PCs. There are actually three different PC keyboards: the original PC keyboard, with 84 keys; the AT keyboard, also with 84 keys; and the enhanced keyboard, with 101 keys. The three differ somewhat in the placement of function keys, the Control key, the Return key, and the Shift keys.
In addition to these keys, IBM keyboards contain the following keys: Page Up, Page Down, Home, End, Insert, Pause, Num Lock, Scroll Lock, Break, Caps Lock, Print Screen.
There are several different types of keyboards for the Apple Macintosh. All of them are called ADB keyboards because they connect to the Apple Desktop bus (ADB). The two main varieties of Macintosh keyboards are the standard keyboard and the extended keyboard, which has 15 additional special-function keys.
Mousea hand-operated electronic device that controls the coordinates of a cursor on your computer screen as you move it around on a pad; on the bottom of the mouse is a ball that rolls on the surface of the pad; "a mouse takes much more room than a trackball
PrinterA device that prints text or illustrations on paper. There are many different types of printers. In terms of the technology utilized, printers fall into the following categories:
daisy-wheel: Similar to a ball-head typewriter, this type of printer has a plastic or metal wheel on which the shape of each character stands out in relief. A hammer presses the wheel against a ribbon, which in turn makes an ink stain in the shape of the character on the paper.Daisy-wheel printers produce letter-quality print but cannot print graphics.
dot-matrix: Creates characters by striking pins against an ink ribbon. Each pin makes a dot, and combinations of dots form characters and illustrations.
ink-jet: Sprays ink at a sheet of paper. Ink-jet printers produce high-quality text and graphics.
laser: Uses the same technology as copy machines. Laser printers produce very high quality text and graphics.
LCD & LED : Similar to a laser printer, but uses liquid crystals or light-emitting diodes rather than a laser to produce an image on the drum.
line printer: Contains a chain of characters or pins that print an entire line at one time. Line printers are very fast, but produce low-quality print.
thermal printer: An inexpensive printer that works by pushing heated pins against heat-sensitive paper. Thermal printers are widely used in calculators and fax machines.
Printers are also classified by the following characteristics:
quality of type: The output produced by printers is said to be either letter quality (as good as a typewriter), near letter quality, or draft quality. Only daisy-wheel, ink-jet, and laser printers produce letter-quality type. Some dot-matrix printers claim letter-quality print, but if you look closely, you can see the difference.
speed: Measured in characters per second (cps) or pages per minute (ppm), the speed of printers varies widely. Daisy-wheel printers tend to be the slowest, printing about 30 cps. Line printers are fastest (up to 3,000 lines per minute). Dot-matrix printers can print up to 500 cps, and laser printers range from about 4 to 20 text pages per minute.
impact or non-impact: Impact printers include all printers that work by striking an ink ribbon. Daisy-wheel, dot-matrix, and line printers are impact printers. Non-impact printers include laser printers and ink-jet printers. The important difference between impact and non-impact printers is that impact printers are much noisier.
graphics: Some printers (daisy-wheel and line printers) can print only text. Other printers can print both text and graphics.
fonts : Some printers, notably dot-matrix printers, are limited to one or a few fonts. In contrast, laser and ink-jet printers are capable of printing an almost unlimited variety of fonts. Daisy-wheel printers can also print different fonts, but you need to change the daisy wheel, making it difficult to mix fonts in the same document
daisy-wheel: Similar to a ball-head typewriter, this type of printer has a plastic or metal wheel on which the shape of each character stands out in relief. A hammer presses the wheel against a ribbon, which in turn makes an ink stain in the shape of the character on the paper.Daisy-wheel printers produce letter-quality print but cannot print graphics.
dot-matrix: Creates characters by striking pins against an ink ribbon. Each pin makes a dot, and combinations of dots form characters and illustrations.
ink-jet: Sprays ink at a sheet of paper. Ink-jet printers produce high-quality text and graphics.
laser: Uses the same technology as copy machines. Laser printers produce very high quality text and graphics.
LCD & LED : Similar to a laser printer, but uses liquid crystals or light-emitting diodes rather than a laser to produce an image on the drum.
line printer: Contains a chain of characters or pins that print an entire line at one time. Line printers are very fast, but produce low-quality print.
thermal printer: An inexpensive printer that works by pushing heated pins against heat-sensitive paper. Thermal printers are widely used in calculators and fax machines.
Printers are also classified by the following characteristics:
quality of type: The output produced by printers is said to be either letter quality (as good as a typewriter), near letter quality, or draft quality. Only daisy-wheel, ink-jet, and laser printers produce letter-quality type. Some dot-matrix printers claim letter-quality print, but if you look closely, you can see the difference.
speed: Measured in characters per second (cps) or pages per minute (ppm), the speed of printers varies widely. Daisy-wheel printers tend to be the slowest, printing about 30 cps. Line printers are fastest (up to 3,000 lines per minute). Dot-matrix printers can print up to 500 cps, and laser printers range from about 4 to 20 text pages per minute.
impact or non-impact: Impact printers include all printers that work by striking an ink ribbon. Daisy-wheel, dot-matrix, and line printers are impact printers. Non-impact printers include laser printers and ink-jet printers. The important difference between impact and non-impact printers is that impact printers are much noisier.
graphics: Some printers (daisy-wheel and line printers) can print only text. Other printers can print both text and graphics.
fonts : Some printers, notably dot-matrix printers, are limited to one or a few fonts. In contrast, laser and ink-jet printers are capable of printing an almost unlimited variety of fonts. Daisy-wheel printers can also print different fonts, but you need to change the daisy wheel, making it difficult to mix fonts in the same document
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