Motherboard

fig.1 - Motherboard

Motherboard, in computer science, the main circuit board in a computer. The most important computer chips and other electronic components that give function to a computer are located on the motherboard. The motherboard is a printed circuit board that connects the various elements on it through the use of traces, or electrical pathways. The motherboard is indispensable to the computer and provides the main computing capability.
Personal computers normally have one central processing unit (CPU), or microprocessor, which is located with other chips on the motherboard. The manufacturer and model of the CPU chip carried by the motherboard is a key criterion for designating the speed and other capabilities of the computer. The CPU in many personal computers is not permanently attached to the motherboard, but is instead plugged into a socket so that it may be removed and upgraded.
Motherboards also contain important computing components, such as the basic input/output system (BIOS), which contains the basic set of instructions required to control the computer when it is first turned on; different types of memory chips such as random access memory (RAM) and cache memory; mouse, keyboard, and monitor control circuitry; and logic chips that control various parts of the computer's function. Having as many of the key components of the computer as possible on the motherboard improves the speed and operation of the computer.
Users may expand their computer's capability by inserting an expansion board into special expansion slots on the motherboard. Expansion slots are standard with nearly all personal computers and offer faster speed, better graphics capabilities, communication capability with other computers, and audio and video capabilities. Expansion slots come in either half or full size, and can transfer 8 or 16 bits (the smallest units of information that a computer can process) at a time, respectively.
The pathways that carry data on the motherboard are called buses. The amount of data that can be transmitted at one time between a device, such as a printer or monitor, and the CPU affects the speed at which programs run. For this reason, buses are designed to carry as much data as possible. To work properly, expansion boards must conform to bus standards such as integrated drive electronics (IDE), Extended Industry Standard Architecture (EISA), or small computer system interface (SCSI).

The Microprocessor (USLI Chip)

Description

fig.2 - Athlon Processor

Microprocessor, electronic circuit that functions as the central processing unit (CPU) of a computer, providing computational control. Microprocessors are also used in other advanced electronic systems, such as computer printers, automobiles, and jet airliners. In 1995 about 4 billion microprocessors were produced worldwide.
The microprocessor is one type of ultra-large-scale integrated circuit. Integrated circuits, also known as microchips or chips, are complex electronic circuits consisting of extremely tiny components formed on a single, thin, flat piece of material known as a semiconductor. Modern microprocessors incorporate as many as ten million transistors (which act as electronic amplifiers, oscillators, or, most commonly, switches), in addition to other components such as resistors, diodes, capacitors, and wires, all packed into an area about the size of a postage stamp.
A microprocessor consists of several different sections: The arithmetic/logic unit (ALU) performs calculations on numbers and makes logical decisions; the registers are special memory locations for storing temporary information much as a scratch pad does; the control unit deciphers programs; buses carry digital information throughout the chip and computer; and local memory supports on-chip computation.
More complex microprocessors often contain other sections-such as sections of specialized memory, called cache memory, to speed up access to external data-storage devices. Modern microprocessors operate with bus widths of 64 bits (binary digits, or units of information represented as 1s and 0s), meaning that 64 bits of data can be transferred at the same time.
A crystal oscillator in the computer provides a clock signal to coordinate all activities of the microprocessor. The clock speed of the most advanced microprocessors is about 600 megahertz (MHz)-about 600 million cycles per second-allowing about a billion computer instructions to be executed every second.
Information is stored in a CPU memory location called a register. Registers can be thought of as the CPU's tiny scratchpad, temporarily storing instructions or data. When a program is run, one register called the program counter keeps track of which program instruction comes next. The CPU's control unit coordinates and times the CPU's functions, and it retrieves the next instruction from memory.
In a typical sequence, the CPU locates the next instruction in the appropriate memory device. The instruction then travels along the bus from the computer's memory to the CPU, where it is stored in a special instruction register. Meanwhile, the program counter is incremented to prepare for the next instruction. The current instruction is analyzed by a decoder, which determines what the instruction will do. Any data the instruction needs are retrieved via the bus and placed in the CPU's registers. The CPU executes the instruction, and the results are stored in another register or copied to specific memory locations.

Computer memory

Because the microprocessor alone cannot accommodate the large amount of memory required to store program instructions and data, such as the text in a word-processing program, transistors can be used as memory elements in combination with the microprocessor.
Separate integrated circuits, called random-access memory (RAM) chips, which contain large numbers of transistors, are used in conjunction with the microprocessor to provide the needed memory.
Dynamic RAM (DRAM) in computer science, a form of semiconductor random access memory (RAM). Dynamic RAMs store information in integrated circuits that contain capacitors. Because capacitors lose their charge over time, dynamic RAM boards must include logic to "refresh" (recharge) the RAM chips continuously. While a dynamic RAM is being refreshed, it cannot be read by the processor; if the processor must read the RAM while it is being refreshed, one or more wait states occur. Because their internal circuitry is simple, dynamic RAMs are more commonly used than static RAMs, even though they are slower. A dynamic RAM can hold approximately four times as much data as a static RAM chip of the same complexity.
Static RAM (SRAM), in computer science, a form of semiconductormemory (RAM). Static RAM storage is based on the logic circuit known as a flip-flop, which retains the information stored in it as long as there is enough power to run the device. A static RAM chip can store only about one-fourth as much data as a dynamic RAM chip of the same complexity, but static RAM does not require refreshing and is usually much faster than dynamic RAM. It is also more expensive. Static RAMs are usually reserved for use in caches.
ROM, acronym for read-only memory. In computer science, semiconductor-based memory that contains instructions or data that can be read but not modified. To create a ROM chip, the designer supplies a semiconductor manufacturer with the instructions or data to be stored; the manufacturer then produces one or more chips containing those instructions or data. Because creating ROM chips involves a manufacturing process, it is economically viable only if the ROM chips are produced in large quantities; experimental designs or small volumes are best handled using PROM or EPROM. In general usage, the term ROM often means any read-only device, including PROM and EPROM.
EPROM, in computer science, acronym for erasable programmable read-only memory. Also called reprogrammable read-only memory (RPROM). EPROMs are nonvolatile memory chips that are programmed after they are manufactured. EPROMs are a good way for hardware vendors to put variable or constantly changing code into a prototype system when the cost of producing many PROM chips would be prohibitive. EPROMs differ from PROMs in that they can be erased, generally by removing a protective cover from the top of the chip package and exposing the semiconductor material to ultraviolet light, and can be reprogrammed after having been erased. Although EPROMs are more expensive than PROMs, they can be more cost-effective in the long run if many changes are needed.

PROM, acronym for programmable read-only memory. In computer science, a type of read-only memory (ROM) that allows data to be written into the device with hardware called a PROM programmer. After a PROM has been programmed, it is dedicated to that data, and it cannot be reprogrammed. Because ROMs are cost-effective only when produced in large volumes, PROMs are used during the prototyping stage of the design. New PROMs can be created and discarded as needed until the design is perfected.

Disk drives

fig.3 - CD-ROM Unit	fig.4 - Hard-Drive

Disk Drive, in computer science, a device that reads or writes data, or both, on a disk medium. The disk medium may be either magnetic, as with floppy disks or hard disks; optical, as with CD-ROM (compact disk-read only memory) disks; or a combination of the two, as with magneto-optical disks. Nearly all computers come equipped with drives for these types of disks, and the drives are usually inside the computer, but may also be connected as external, or peripheral, devices.
The main components of a disk drive are the motor, which rotates the disk; the read-write mechanism; and the logic board, which receives commands from the operating system to place or retrieve information on the disk. To read or write information to a disk, drives use various methods. Floppy and hard drives use a small magnetic head to magnetize portions of the disk surface, CD-ROM and WORM (Write-Once-Read-Many) drives use lasers to read information, and magneto-optical drives use a combination of magnetic and optical techniques to store and retrieve information.
Floppy and hard disk drives store information on magnetic disks. The disk itself is a thin, flexible piece of plastic with tiny magnetic particles imbedded in its surface. To write data to the disk, the read-write head creates a small magnetic field that aligns the magnetic poles of the particles on the surface of the disk directly beneath the head. Particles aligned in one direction represent a 0 while particles aligned in the opposite direction represent a 1. To read data from a disk, the drive head scans the surface of the disk. The magnetic fields of the particles in the disk induce an alternating electric current in the read-write head, which is then translated into the series of 1s and 0s that the computer understands.
Unlike hard or floppy disks, CD-ROM drives are unable to write data to the CD. Data is initially written to CD-ROM discs by burning microscopic pits into the disk's reflective surface with a laser. To read the information contained on the disk, the drive shines a low-power laser beam onto the surface. When the laser light hits flat spots on the reflective surface of the CD, it bounces back to a photo detector, which records the impulse as a 0. When the laser light hits pits in the surface, it does not reflect light back to the photo detector, and this absence of light corresponds to a 1. Most CD-ROM drives are only capable of reading data and cannot write data to the CD. WORM drives, however, are able to both etch blank CDs and to read data from them.
Magneto-optical (MO) drives combine optical and magnetic technology to read from and write to discs that have the appearance of CD-ROMs in plastic, floppy-disk cases. MO drives can rewrite the MO discs without limitation just as magnetic drives rewrite magnetic media. Although more expensive than standard magnetic or optical drives, MO drives combine speed, large capacity, and high durability of data.

Useful links

Ic - integrated circuit | Transistor | Media galery