Memory

Memory

Memory: 

A memory is simply sort of a human brain. it's wont to store data and directions. Computer hardware is that the cupboard space in computer where data is to be processed and directions required for processing are stored. The memory is split into sizable amount of small parts called cells. All location or cell is featured a unique address which changes from zero to (memory size -1). As an example if computer has 64k words, then this memory unit has 64 * 1024=65536 memory locations. The address of those locations varies from 0 to 65535.

Memory is primarily of three types

* Cache Memory

* Primary Memory/Main Memory

* Secondary Memory 

Cache Memory:

 Cache memory could be a very high speed semiconductor memory which might speed up CPU. This works as a buffer between the CPU and main memory. It’s wont to hold those parts of information and program which are most often employed by CPU. The parts of knowledge and programs are transferred from disk to cache memory by software system, from where CPU can access them.

Advantages: Advantages of cache memory are as follows:

 *Cache memory is quicker than main memory.

 *It consumes less time interval as compared to main memory.

 * It stores the program that may be executed within a brief period of your time.

  *It stores data for temporary use.

Disadvantages:

Disadvantages of cache memory are as follows:

* Cache memory has limited capacity.

 * it's very expensive.

 Primary Memory (Main Memory):

 Primary memory holds only those data and directions on which pc is currently working. it's limited capacity and data is lost when power is changed. It’s generally made from semiconductor unit. These memories don't seem to be as fast as registers. The information and instruction required to be processed reside in main memory. It’s divided into two subcategories RAM and ROM.

Characteristics of Main Memory

* These are semiconductor memories

* it's called main memory.

* Usually volatile memory.

* Data is lost just in case power is shifted.

* it's remembering of the pc.

* Faster than secondary memories.

* A computer cannot run without primary memory.

 Secondary Memory: 

This type of memory is additionally referred to as external memory or non-volatile. it's slower than main memory. These are used for storing data/Information permanently. CPU directly doesn't access these memories instead they're accessed via input-output routines. Contents of secondary memories are first transferred to main memory, so CPU can access it. as an example : disk, CD-ROM, DVD etc.

Characteristic of Secondary Memory

* These are magnetic and optical memories

* it's referred to as backup memory.

* it's non-volatile memory.

* Data is permanently stored whether or not power is transitioned.

* it's used for storage of information in a very computer.

* Computer may run without secondary memory.

* Slower than primary memories.

RAM:

RAM (Random Access Memory) is that the internal memory of the CPU for storing data, program and program result. it's read/write memory which stores data until the machine is functioning. As soon because the machine is transitioned, data is erased. Access time in RAM is independent of the address that's, each storage location inside the memory is as easy to achieve as other locations and takes the identical amount of your time. Data within the RAM will be accessed randomly but it's very expensive. RAM is volatile, i.e. data stored in it's lost after we turn off the pc or if there's an influence failure. Hence a backup uninterruptible power system(UPS) is commonly used with computers. RAM is tiny, both in terms of its physical size and within the amount of knowledge it can hold.

RAM is of two types

* Static RAM (SRAM)

* Dynamic RAM (DRAM)

Primary Memory Static RAM (SRAM) :The word static indicates that the memory retains its contents as long as power is being supplied. However, data is lost when the ability gets down because of volatile nature. SRAM chips is made with a matrix of 6-transistors and have not  any capacitors. Transistors don't require power to stop leakage, so SRAM needn't should be refreshed on an everyday basis. Because of the additional space within the matrix, SRAM uses more chips than DRAM for the identical amount of space for storing, thus making the manufacturing costs higher. So SRAM is employed as cache memory and has in no time access.

Characteristic of the Static RAM

* it's long life

* there's no have to refresh

* Faster

* Used as cache memory

* Large size

* Expensive

* High power consumption

Dynamic RAM (DRAM) DRAM: unlike SRAM, must be continually refreshed so as to keep up the information. this can be done by placing the memory on a refresh circuit that rewrites the info several hundred times per second. DRAM is employed for many system memory because it's cheap and tiny. All DRAMs are made of memory cells which are composed of 1 capacitor and one transistor.

Characteristics of the Dynamic RAM

* it's short data lifetime

* must be refreshed continuously

* Slower as compared to SRAM

* Used as RAM

* Lesser in size

* less costly

* Less power consumption

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ROM:

ROM stands for Read Only Memory. The memory from which we will only read but cannot compose it. this sort of memory is non-volatile. the knowledge is stored permanently in such memories during manufacture. A ROM, stores such instructions that are required to start out a computer. This operation is remarked as bootstrap. ROM chips aren't only employed in the pc but also in other electronic items like washer and microwave. Different types of ROM are there in different variety of styles. In ROM,MROM (Masked ROM) is the very first ROMs were there in hard-wired devices that contained a pre-programmed set of information or instructions. These quite ROMs are referred to as masked ROMs which are inexpensive.

PROM (Programmable Read only Memory):

PROM is computer memory that may be modified just one occasion by a user. The user buys a blank PROM and enters the required contents employing a PROM program. In PROM chip, small chips are there. There are small fuses which has burnt open during programming. It may be programmed just one occasion and isn't erasable.

EPROM(Erasable and Programmable Read Only Memory): 

The EPROM may be erased by exposing it to ultra-violet light for a duration of up to 40 minutes. Usually, an EPROM eraser achieves this function. When programming is done then an electrical charge is trapped in an insulated gate region. The charge is retained for quite ten years because the charge has no leakage path. For erasing this charge, ultra-violet light is responded to a quartz window (lid). This exposure to ultra-violet light dissipates the charge. When the quartz lid is normally used that time it is sealed with a sticker. 

EEPROM (Electrically Erasable and Programmable Read Only Memory):

The EEPROM is programmed and erased electrically. It may be erased and reprogrammed about ten thousand-fold. It takes time for both erasing and programming is about 4 to 10 ms (milli second). In EEPROM, any location may be selectively erased and programmed. EEPROMs will be erased one byte at a time, instead of erasing the whole chip. Hence, the method of re-programming is flexible but slow.

 Advantages of ROM The advantages of ROM are as follows:

 * Non-volatile in nature

* These cannot be accidentally changed

* Cheaper than RAMs

* Easy to check

* More reliable than RAMs

* These are static and don't require refreshing

* Its contents are always known and may be verified