The hard drive, alternatively referred to as a hard disk drive and abbreviated as HD or HDD, the hard drive is the computer's main storage media device that permanently stores all data on the computer. The hard drive was first introduced on September 13, 1956 and consists of one or more hard drive platters inside of air sealed casing. Most computer hard drives are in an internal drive bay at the front of the computer and connect to the motherboard using either A T A, S C S I, or a S A T A cable and power cable. Data sent to and from the hard drive is interpreted by the disk controller, which tells the hard drive what to do and how to move the components within the drive. When the operating system needs to read or write information, it examines the hard drives File Allocation Table (FAT) to determine file location and available areas. Once this has been determined, the disk controller instructs the actuator to move the read/write arm and align the read/write head. Because files are often scattered throughout the platter, the head will often need to move to different locations to access all information. The Hard Drive

A Digital Versatile Disc - Read Only Memory, or DVD-ROM, is a media storage disk that closely resembles a CD or compact disc. The major difference is that the DVD is formatted to hold far more data. A CD commonly has a capacity of 650 megabytes, while the smallest capacity DVD can store about seven times more data, or 4.38 gigabytes (GB). There are various kinds of DVDs, but the DVD-ROM refers to a read-only disc, or a disc that cannot be written over. A DVD movie bought from the local video store is a good example. Blank DVDs with designations like "DVD-R" and "DVD+R" are formatted, recordable DVDs. The -R and +R refer to competing format standards, but both will record movies, audio, or other data. The disc encodes data in the form of a spiralling trail of pits and lands separated by nanometers. The trail starts at the centreof the DVD, and winds around times until it reaches the outer edge. In the case of a double layer disk, the trail continues on a second layer of material. If the disc is also double-sided, the trail of pits and lands extends to side two. DVD-ROM

In electronic systems, a heat sink is a passive heat exchanger that cools a device by dissipating heat into the surrounding medium. In computers, heat sinks are used to cool central processing units or graphics processors. Heat sinks are used with high-power semiconductor devices such as power transistors and optoelectronics such as lasers and light emitting diodes (LEDs), where the heat dissipation ability of the basic device is insufficient to moderate its temperature. A heat sink is designed to maximize its surface area in contact with the cooling medium surrounding it, such as the air. Air velocity, choice of material, protrusion design and surface treatment are factors that affect the performance of a heat sink. Heat sink attachment methods and thermal interface materials also affect the die temperature of the integrated circuit. Thermal adhesive or thermal grease improve the heat sink's performance by filling air gaps between the heat sink and the device. Heat Sink

A computer fan is any fan inside, or attached to, a computer case used for active cooling, and may refer to fans that draw cooler air into the case from the outside, expel warm air from inside, or move air across a heat sink to cool a particular component. As processors, graphics cards, RAM and other components in computers have increased in speed and power consumption, the amount of heat produced by these components as a side-effect of normal operation has also increased. These components need to be kept within a specified temperature range to prevent overheating, instability malfunction and damage leading to a shortened component lifespan. Computer Fan

A power supply unit converts AC to low-voltage DC power for the internal components of a computer. Modern personal computers universally use a switched-mode power supply. Some power supplies have a manual selector for input voltage, while others automatically adapt to the supply voltage. Most modern desktop personal computer power supplies change to the ATX spec, which has form factor and voltage tolerances. While an ATX power supply is connected to the mains supply, it always delivers a 5 V standby (5VSB) voltage ensuring that the standby functions on the computer and certain peripherals are powered. ATX power supplies are switched on and off by a signal from the motherboard. They also give a signal to the motherboard to signify when the DC voltages are in spec, so that the computer can safely power up and boot. Power Supply Unit

A central processing unit (CPU)) is the hardware in a computer that carries out the instructions of a computer program by performing the basic arithmetical, logical, and input/output operations of the system. Computers can have more than one CPU; this is called multiprocessing. Modern CPUs are microprocessors, meaning contained on a single chip. Some integrated circuits (ICs) can contain multiple CPUs on a single chip; those ICs are called multi- core processors. An IC containing a CPU can also contain peripheral devices, and other components of a computer system; this is called a system on a chip (SoC). Two typical components of a CPU are the arithmetic logic unit (ALU), which performs arithmetic and logical operations, and the control unit (CU), which extracts instructions from memory and decodes and executes them, calling on the ALU when necessary. Not all computational systems rely on a central processing unit. An array processor or vector processor has multiple parallel computing elements, with no one unit considered the "center". In the distributed computing model, problems are solved by a distributed interconnected set of processors. Central Processing Unit