Computer CPU / Memory

·         CPU is considered as the brain of the computer.

·         CPU performs all types of data processing operations.

·         It stores data , intermediate resulta and instructions(program).

·         It controls the operation of all parts of computer.

CPU itself has following three components.

·         Memory Or Storage Unit:

·         Control Unit

·         ALU(Arithmetic Logic Unit)

Memory Or Storage Unit:

This unit can store instruction, data and intermediate results.This unit supplies information to the other units of the computer when needed.It is also known as internal storage unit or main memory or primary storage or Random access memory(RAM).

Its size affects speed, power and capability.There are primary memory and secondary memory two types of memories in the computer.Function of Memory Unit are:

·         It stores all the data to be processed and the instructions required for processing.

·         It stores intermediate results of processing.

·         It stores final results of processing before these results are released to an output device.

·         All inputs and outputs are transmitted through main memory.

Control Unit

This unit controls the operations of all parts of computer.It does not carry out any actual data processing operations.

Functions of this unit are

·         It is responsible for controlling the transfer of data and instructions among other units of a computer.

·         It manages and coordinates all the units of the computer.

·         It obtains the instructions from the memory, interprets them and directs the operation of the computer.

·         It communicates with Input/Output devices for transfer of data or results from storage.

·         It does not process or store data.

ALU(Arithmetic Logic Unit)

This unit consists of two subsection namely

·         Arithmetic section

·         Logic Section

ARITHMETIC SECTION

Function of Arithmetic section is to perform arithmetic operations like addition, subtraction, multiplication and division.All complex operations are done by making repetitive use of above operations.

LOGIC SECTION

Function of logic section is to perform logic operations such as comparing, selecting, matching and merging of data.

computer ram

A RAM constitutes the internal memory of the CPU for storing data, program and program result. It is read/write memory. It is called random access memory (RAM).

Since access time in RAM is independent of the address to the word that is, each storage location inside the memory is as easy to reach as other location & takes the same amount of time. We can reach into the memory at random & extremely fast but can also be quite expensive.

RAM is volatile, i.e. data stored in it is lost when we switch off the computer or if there is a power failure. Hence a backup uninterruptible power system(UPS) is often used with computers. RAM is small , both in terms of its physical size and in the amount of data it can hold.

RAM is of two types

·         Static RAM (SRAM)

·         Dynamic RAM (DRAM)

Static RAM (SRAM)

The word static indicates that the memory retains its contents as long as power remains applied. However, data is lost when the power gets down due to volatile nature. SRAM chips use a matrix of 6-transistors and no capacitors. Transistors do not require power to prevent leakage, so SRAM need not have to be refreshed on a regular basis.

Because of the extra space in the matrix, SRAM uses more chips than DRAM for the same amount of storage space, thus making the manufacturing costs higher.

Static RAM is used as cache memory needs to be very fast and small.

Characteristic of the Static RAM

·         It has long data lifetime

·         There is no need to refresh

·         Faster

·         Used as cache memory

·         Large size

·         Expensive

·         High power consumption

Dynamic RAM (DRAM)

DRAM, unlike SRAM, must be continually refreshed in order for it to maintain the data. This is done by placing the memory on a refresh circuit that rewrites the data several hundred times per second. DRAM is used for most system memory because it is cheap and small. All DRAMs are made up of memory cells. These cells are composed of one capacitor and one transistor.

Characteristic of the Dynamic RAM

·         It has short data lifetime

·         Need to refresh continuously

·         Slower as compared to SRAM

·         Used as RAM

·         lesser in size

·         Less expensive

·         Less power consumption

computer memory

A memory is just like a human brain. It is used to store data and instruction. Computer memory is the storage space in computer where data is to be processed and instructions required for processing are stored.

The memory is divided into large number of small parts. Each part is called cell. Each location or cell has a unique address which varies from zero to memory size minus one.

For example if computer has 64k words, then this memory unit has 64 * 1024=65536 memory location. The address of these locations varies from 0 to 65535.

Memory is primarily of three types

·         Cache Memory

·         Primary Memory/Main Memory

·         Secondary Memory

Cache Memory

Cache memory is a very high speed semiconductor memory which can speed up CPU. It acts as a buffer between the CPU and main memory.

It is used to hold those parts of data and program which are most frequently used by CPU. The parts of data and programs are transferred from disk to cache memory by operating system, from where CPU can access them.

ADVANTAGE

·         Cache memory is faster than main memory.

·         It consumes less access time as compared to main memory.

·         It stores the program that can be executed within a short period of time.

·         It stores data for temporary use.

DISADVANTAGE:

·         Cache memory has limited capacity.

·         It is very expensive.

Primary Memory (Main Memory)

Primary memory holds only those data and instructions on which computer is currently working. It has limited capacity and data get lost when power is switched off.

It is generally made up of semiconductor device. These memories are not as fast as registers. The data and instruction required to be processed earlier reside in main memory. It is divided into two subcategories RAM and ROM.

Characteristic of Main Memory

·         These are semiconductor memories.

·         It known as main memory.

·         Usually volatile memory.

·         Data is lost in case power is switch off.

·         It is working memory of the computer.

·         Faster than secondary memories.

·         A computer cannot run without primary memory.

Secondary Memory

This type of memory is also known as external memory or non-volatile. It is slower than main memory. These are used for storing Data/Information permanently.

CPU directly does not access these memories instead they are accessed via input-output routines. Contents of secondary memories are first transferred to main memory, and then CPU can access it.For example: disk, CD-ROM,DVD etc.

Characteristic of Secondary Memory

·         These are magnetic and optical memories.

·         It is known as backup memory.

·         It is non-volatile memory.

·         Data is permanently stored even if power is switched off.

·         It is used for storage of the data in the computer.

·         Computer may run without secondary memory.

·         Slower than primary memories.