Computer Hardware

The hardware of computer is divided into three broad categories:

1. Processor/Processing Unit
2. Memory(Internal & External)
3. I/O (input/output).

Processor

The processor is the part of the computer that actually does the computations. This is sometimes called an MPU (Main Processor Unit) or CPU (Central Processing Unit or Central Processor Unit).
A processor typically contains an Arithmetic & Logic unit (ALU), Control Unit (CU).

Arithmetic & Logic Unit (ALU)

An arithmetic & logic unit (ALU) performs integer arithmetic and logic operations. It also performs shift and rotate operations and other specialized operations. Usually floating point arithmetic is performed by a dedicated Floating Point Unit (FPU), which may be implemented as a co-processor.

Control Unit (CU)

Control units are in charge of the computer. Control units fetch and decode machine instructions. Control units may also control some external devices.

Main Storage

Main storage is also called memory or internal memory (to distinguish from external memory, such as hard drives).

RAM is Random Access Memory, and is the basic kind of internal memory. RAM is called “random access” because the processor or computer can access any location in memory (as contrasted with sequential access devices, which must be accessed in order). RAM has been made from transistors, integrated circuits, magnetic core, or anything that can hold and store binary values (one/zero, plus/minus, open/close, positive/negative, high/low, etc.).

Static RAM is called static because it will continue to hold and store information even when power is removed. Magnetic cores are examples of static memory.
Dynamic RAM is called dynamic because it loses all data when power is removed. Transistors and integrated circuits are examples of dynamic memory.

ROM is Read Only Memory (it is also random access, but only for read). ROM is typically used to store things that will never change for the life of the computer, such as low level portions of an operating system.

Cache (pronounced cash) Memory :
Cache (pronounced cash) memory is extremely fast memory that is built into a computer’s central processing unit (CPU), or located next to it on a separate chip. The CPU uses cache memory to store instructions that are repeatedly required to run programs, improving overall system speed. The advantage of cache memory is that the CPU does not have to use the motherboard’s system bus for data transfer. Whenever data must be passed through the system bus, the data transfer speed slows to the motherboard’s capability. The CPU can process data much faster by avoiding the bottleneck created by the system bus.

Cache built into the CPU itself is referred to as Level 1 (L1) cache. Cache that resides on a separate chip next to the CPU is called Level 2 (L2) cache. Some CPUs have both L1 and L2 cache built-in and designate the separate cache chip as Level 3 (L3) cache.


Data storage device

Computer data storage, often called storage or memory, refers to computer components and recording media that retain digital data used for computing for some interval of time. Computer data storage provides one of the core functions of the modern computer, that of information retention. It is one of the fundamental components of all modern computers A data storage device is a device for recording (storing) information (data).

Primary Storage

• It is directly accessable by CPU
• It is volatile in nature
• All instruction are stored in primary memory before it can be uesd for processing
• It is fastes among all type of memory
• It has small storage space

Primary storage (or main memory or internal memory), often referred to simply as memory, is the only one directly accessible to the CPU. The CPU continuously reads instructions stored there and executes them as required.

Secondary Storage

• It non-volatile ,that is, data remain stored even when the computer is switched off.
• It is slower than primary memory
• It has large storage space

Secondary storage (or external memory) differs from primary storage in that it is not directly accessible by the CPU. The computer usually uses its input/output channels to access secondary storage and transfers the desired data using intermediate area in primary storage. Secondary storage does not lose the data when the device is powered down—it is non-volatile. In modern computers, hard disk drives are usually used as secondary storage.

Tertiary Storage

• It is slower than secondary memory
• Generally used to store large amount of data
• It needs robotics mechanism to insert and remove
• Used in supercomputer as accessing data is slow from Tertiary Storage Device

Tertiary storage or tertiary memory, provides a third level of storage. Typically it involves a robotic mechanism which will mount (insert) and dismount removable mass storage media into a storage device according to the system's demands; this data is often copied to secondary storage before use. It is primarily used for archival of rarely accessed information since it is much slower than secondary storage. This is primarily useful for extraordinarily large data stores, accessed without human operators.

Off-line storage

• Pen drive is an example of off-line storage device
• It reqiures human operater to insert and remove
• It is portable and can be carried with ease

Off-line storage is a computer data storage on a medium or a device that is not under the control of a processing unit.The medium is recorded, usually in a secondary or tertiary storage device, and then physically removed or disconnected. It must be inserted or connected by a human operator before a computer can access it again. Unlike tertiary storage, it cannot be accessed without human interaction.

Input

Input devices are devices that bring information into a computer. Information and commands are issued to the computer by way of input devices. Input device is used to insert data and instructions for processing in the computer.
Examples of input devices include the keyboard, mouse, modem, joystick, digitizing pen and tablet, microphone, touch screens, scanner, camera.

Output

Output devices are devices that bring information out of a computer and present data in a form that people can understand.
Examples of output devices include monitors, printers, and pen plotters.