Text B PC Hardware Basic

1.Computer case (PC enclosure)

Computer systems are general-purpose devices that may be modified to perform particular tasks or functions. Such general-purpose computers typically include housings for enclosing various components and circuitry associated with operating the general-purpose computers. The computer enclosure is used to protect the components and circuitry housed therein from physical damage, and to prevent electromagnetic signals generated by components of the computer from escaping and causing electromagnetic interference (EMI) to other electronic devices in the vicinity of the computer. A typical computer enclosure includes a chassis, an expansion card seat, a front bezel and a plurality of components connectable to external apparatus and systems. In a typical application, a computer case has a high structural integrity to protect against physical impact, and conductive, shielding materials to reduce EMI emissions. The conductive components of the computer are also grounded to the case to protect users and computer components from electric shock. In assembly, the bezel, the side panels and the cover are directly secured to the base with screws. In order to remove the bezel or the cover, the screws must be disengaged from the base one by one. Some computer enclosures adopt hooks to reduce or even eliminate the need for screws. Hooks formed on panels of the enclosure engage in recesses defined in other panels of the enclosure. Modern computer systems comprise not only a motherboard, but also one or more expansion cards that provide specialized functions. A rear panel of a computer case typically defines a plurality of expansion slots therein. Each expansion card typically comprises a slot cover attached at one of the expansion slots, to correctly position the corresponding expansion card. In most cases, the computer housings take the form of a box, as for example, the housings associated with tower style computers.

2.PC motherboard

A general computer system is basically built with a motherboard, interface cards and peripherals. The motherboard is the physical arrangement that contains the system's basic circuitry and components. The motherboard functions to facilitate communication between each of the internal components of the system, which usually contains a controller chip set, several slots for installing the interface cards, a central processing unit (CPU) and several memory module slots for accommodating the memory modules. Typically, a computer motherboard includes many input/output (I/O) ports for connecting to various peripherals, and these I/O ports are arranged on the personal computer. A computer motherboard comprises a large printed circuit board having a number of components mounted thereon, including a processor coupled to a host or local bus, a chip set, system memory coupled to a memory bus, and a Peripheral Component Interconnect (PCI) bus. The motherboard is typically permanently attached to the chassis and is also connected to other internal components via cables or internal connectors. A computer motherboard has a plurality of mounting holes for the mounting of female screw rods to support a circuit board or any of a variety of electronic devices above the motherboard.

3.Computer memory

A computer system is generally comprised of several component parts including a processor, computer memory, a data bus, and other peripheral devices and components. The processor accesses, modifies, and writes data to random access memory. The data contained in computer memory is transferred to the processor through the data bus. Memory is a semiconductor storage device for holding programs or data. There're three basic forms of memories: dynamic storage, non-volatile memory and static memory. In dynamic storage, data must be constantly refreshed and data are erased when power is no longer applied to the cell. In non-volatile memory, data remains permanently in the cell even when power is not applied, and in static memory data does not need to be refreshed but its data is lost when power is no longer applied to the cell. In a computer system, non-volatile memory is used for long-term storage of programs and data which seldom or never changes, and volatile memory devices are used for the short-term storage of program instructions and data during the execution of a program. According to the application functions, memories can be categorized into read only memory (ROM) and random access memory (RAM). As the name implies, the read only memory is only read accessible. A ROM device cannot be rewritten once it has been programmed. Embedded software applications use ROM to store embedded code and data records. The processor in an embedded software application retrieves each instruction from ROM and executes it. The random access memory can perform both write and read operations. RAM also differs from ROM in that when power is disconnected from RAM, the data stored in random access memory is lost whereas when power is disconnected from ROM the data stored in read only memory remains. The read only memory is further categorized into programmable read only memory (PROM), erasable programmable read only memory (EPROM), and electrically erasable programmable read only memory (EEPROM). Whereas, the random access memory can be further categorized into a static random access memory (SRAM) and a dynamic random access memory (DRAM). Static read/write random-access memory (SRAM) is a type of volatile memory in which the data, once it is written to a memory location, remains stored there as long as power is applied to the memory chip. Dynamic random access memories (DRAMs) are a mainstay in the semiconductor industry. DRAMs are data storage devices that store data as charge on a storage capacitor. In DRAM, the data stored at each location is periodically refreshed by reading it and then writing it back again to the same location, or else it disappears. One type of DRAM transfers information synchronously with a clock signal. This type of DRAM is referred to as synchronous DRAM (SDRAM). SDRAM transfers information once every clock cycle of the clock signal, such as the rising edge of the clock signal. Nevertheless, DDR DRAM transfers data on each edge of the clock signal, thus doubling the peak throughput of the memory device as compared with SDRAM. The magnetoresistive random access memory (MRAM) is an alternative memory device to DRAM. An MRAM device uses magnetic orientations to retain data in its memory cells. MRAM devices are relatively fast, are nonvolatile, consume relatively little power, and do not suffer from a write cycle limitation. PROM allows the device manufacturer to program the embedded code. This allows for revisions in the code but still does not allow for modification or erasure of the ROM once it has been programmed. EPROM, EEPROM and flash memory are a growing class of non-volatile storage integrated circuits based on floating gate transistors. Flash memory devices typically use a one-transistor memory cell that allows for high memory densities, high reliability, and low power consumption. Common uses for flash memory include personal computers, personal digital assistants (PDAs), digital cameras, and cellular phones.

4.Computer processor

Data processing systems are systems that manipulate, process, and store data. The processor is the brain of a computer system, performing all calculations and other data manipulation under the control of application and operating system software. A computer data processor is often referred to as a microprocessor. Modern computer systems include a microprocessor and a system memory for storing instructions to be executed by the microprocessor and data to be processed by the instructions. A microprocessor is a circuit that combines the instruction-handling, arithmetic, and logical operations of a computer on a single semiconductor integrated circuit. Microprocessors can be grouped into two general classes, namely general-purpose microprocessors and special-purpose microprocessors. Generalpurpose microprocessors are designed to be programmable by the user to perform any of a wide range of tasks, and are therefore often used as CPU in equipment such as personal computers. A micro-controller, or embedded controller, is similar to a microprocessor as used in a personal computer, but with a great deal of additional functionality combined onto the same monolithic semiconductor substrate. Special purpose microprocessors are designed to provide performance improvement for specific predetermined arithmetic and logical functions for which the user intends to use the microprocessor. A digital signal processor (DSP) is a special purpose microprocessor that performs computations which generally require large numbers of arithmetic operations to be performed rapidly. Digital signal processing is connected with the representation of signals by sequences of numbers or symbols and the processing of these signals. Microprocessors often employ the use of pipelining to enhance performance. With pipeline architecture, the tasks performed by a processor are broken down into a sequence of functional units referred to as stages or pipeline stages. Superscalar microprocessors typically execute more than one instruction per clock cycle. Superscalar microprocessors allow parallel instruction execution in two or more instruction execution pipelines. The goal of superscalar and superpipeline microprocessors is to execute multiple instructions per microprocessor clock cycle. In a data processor, a clock signal is generated by a clock generating circuit and various circuit resources operate synchronously with the clock signal. In this way, various kinds of data processing can be executed.

5.Hard disk drive

A hard disk drive (HDD) is a device that stores or reproduces data in a desired storage location by moving its magnetic head to the desired location in a head load state. The hard disk drive is standard equipment for personal computer, server or industrial computer. A hard drive is provided with headers for signal transmission as well as power connector for receiving power from a switching power supply mounted within a computer. A computer hard disk drive typically includes one or more rotatable storage media, or disks upon which data is encoded. The disks are mounted on the shaft of a spindle motor for rotation. Data is encoded on the rotating disks as bits of information using magnetic field reversals grouped in tracks. Hard disk drives contain a plurality of magnetic heads that are coupled to rotating disks. The heads write and read information by magnetizing and sensing the magnetic fields of the disk surfaces. Each magnetic head is attached to a flexure arm to create a subassembly commonly referred to as a head gimbal assembly (HGA). A transducer head supported by an actuator arm is used to read data from or write data to the disks. The head gimbal assemblies are suspended from an actuator arm. The actuator arm has a voice coil motor that can move the heads across the surfaces of the disks. The disks are rotated by a spindle motor of the disk drive. A voice control motor (VCM) attached to the actuator arm controls positioning of the actuator, and thus the transducer head position over a disk. Servo position data read from the disk is processed by the processor, enabling the processor to provide servo control signals to the VCM for proper positioning of a transducer head relative to a disk. Hard disk drive units include a magnetic disk that is capable of storing a large amount of binary information. The magnetic disk is typically coupled to a hub that is rotated by an electric motor, commonly referred to as a spindle motor. The primary function of a spindle motor controller is to regulate the commutation of the spindle motor, which in turn controls the rotation rate of the spindle motor. This rotation rate is controlled by an external hard disk drive controller which provides the spindle motor controller with a digital demand code indicative of a desired rotational rate of the motor. The actuator arm, motors and other components of a typical disk drive unit are relatively small and fragile, and are therefore susceptible to damage when subjected to excessive external shock loads or vibration. For this reason, hard disk drives are usually rigidly mounted to the housing of the computer system by screws or other fastening means. Generally, the HDD is electrically connected with a motherboard of the computer by means of a signal cable assembly and a power cable assembly interconnected between the motherboard and the switching power supply.