Hardware is best described as a device that is physically connected to your computer or something that can be physically touched. A CD-ROM, Monitor, Printer, and video card are all examples of computer hardware. Without any hardware your computer would not exist and software would have nothing to run on. The image to the right is of a webcam, an example of an external hardware peripheral that allows users to make videos and/or pictures and transmit them over the Internet.
The major components of a computer are:
The Motherboard
The CPU or Central Processing Unit
RAM or the Random Access Memory
Sound Card
The Graphics Card
The Power Supply
The Hard Disk or Hard Drive
The Optical Drive - also known as a CD or DVD Drive
Secondary drive
Motherboard
The motherboard is the main component inside the case. It is a large rectangular board with integrated circuitry that connects the rest of the parts of the computer including the CPU, the RAM, the disk drives (CD, DVD, hard disk, or any others) as well as any peripherals connected via the ports or the expansion slots.
Power supply
A power supply unit (PSU) converts alternating current (AC) electric power to low-voltage DC power for the internal components of the computer. Some power supplies have a switch to change between 230 V and 115 V. Other models have automatic sensors that switch input voltage automatically, or are able to accept any voltage between those limits. Power supply units used in computers are nearly always switch mode power supplies (SMPS). The SMPS provides regulated direct current power at the several voltages required by the motherboard and accessories such as disk drives and cooling fans.
Sound card
Enables the computer to output sound to audio devices, as well as accept input from a microphone. Most modern computers have sound cards built-in to the motherboard, though it is common for a user to install a separate sound card as an upgrade. Most sound cards, either built-in or added, have surround sound capabilities.
* The central processing unit (CPU) performs most of the calculations which enable a computer to function, and is sometimes referred to as the "brain" of the computer. It is usually cooled by a heat sink and fan.
The chip set mediates communication between the CPU and the other components of the system, including main memory.
RAM
(Random Access Memory) stores all running processes (applications) and the current running OS.RAM stands for Random Access Memory, and comes as modules in predefined amounts. It is also found directly on the motherboard and usually in one, two or four slots. The memory chips store information, temporarily, for short term use by the CPU. RAM is used to store information for files that are actually being used by the CPU at any given time.
The computer's RAM memory is an entirely different thing from the hard disk "memory". The hard disk stores information "permanently" for long term use
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The graphics card or video card translates information into the graphics and text that appear on the monitor screen.
Most motherboards now include a slot specifically designed for the graphics adapter called the AGP slot. This stands for Advanced Graphics Port.
Modern graphics adapters usually incorporate some memory right on the card to improve their performance.
The Optical Drive
The optical drive is often called a DVD drive, or a CD drive. It sits at the front of the computer for ease of access, and uses a laser to read and write information to CD's and DVD's.
Secondary storage
Hardware that keeps data inside the computer for later use and remains persistent even when the computer has no power.
* Hard disk - for medium-term storage of data.
* Solid-state drive - a device similar to hard disk, but containing no moving parts and stores data in a digital format.
* RAID array controller - a device to manage several internal or external hard disks and optionally some peripherals in order to achieve performance or reliability improvement in what is called a RAID array.
Conclusion
It is generally considered that a fault-tolerant system is composed of a hardware system and a software system. The present work assumes that a hardware system is composed of two units (processors). Two software maintenance policies depending on the priority maintenance for software are proposed. In particular, software maintenance policies are discussed by evaluating the (time dependent) transient solutions of the reliability measures. Formulating Markov process models for two policies, and calculating the reliability measures numerically, two software maintenance policies for the resulting reliability measures are compared.
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