Memory and Storage Devices

 

Memory and Storage Devices

Computer memory is just like the human brain. It is used to collect data and instructions in one place. Computer memory is the storage space in a computer where data is processed and instructions necessary for processing are stored.

 

Memory is divided into a large number of smaller sections. Each part is called a cell. Each location or cell has a unique address that varies from zero to the memory size minus one.

 

Let's see an example if the computer has 64k words then this memory unit has 64*1024 = 65536 memory locations. The address of this location varies from 0 to 65535.

 

Memory is basically of two types.

·         Internal Memory − Cache Memory and Primary/Main memory

·         External Memory − Magnetic disk / Optical disk etc.

 


RAM

RAM constitutes the internal memory of the CPU for storing data, programs and program results. It is read/write memory. This is called Random Access Memory (RAM).

 

Since the access time in RAM is independent of the word address, each storage location within memory is as easy to access as another location and takes the same amount of time. We can access random and extremely fast memory but can also be quite expensive.

 

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

 

Static RAM (SRAM)

The word static indicates that the memory retains its contents as long as power is applied. However, data is lost when the power goes out due to its unstable nature. Transistors do not require power to prevent leakage, so SRAM does not need 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 increasing manufacturing costs.

 

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

 

Dynamic RAM (DRAM)

DRAM, unlike SRAM, must be constantly refreshed to retain data. This is maintained by placing the memory on a refresh circuit that rewrites the data several hundred times per second. DRAM is used mostly for system memory because it is cheap and small, which makes it easy. These cells consist of a capacitor and a transistor.

 

ROM

ROM stands for Read Only Memory. A memory that we can only read from but not write to. This type of memory is non-volatile. Information is permanently stored in such memories during preparation.

 

A ROM stores the instructions necessary to start the computer when the power is first turned on, an operation called bootstrap. ROM chips are used not only in computers but also in other electronic items such as washing machines and microwave ovens.

 

Following are the different types of ROM.

 

MROM (masked ROM)

Long ago ROMs were hardwired devices that contained a pre-programmed set of data or instructions. ROMs of this type are called masked ROMs. This is cheap ROM.

 

PROM (Programmable Read Only Memory)

PROM is read-only memory that can be changed only once by the user. The user purchases a blank PROM and inserts the desired content using the PROM programmer. Inside the PROM chip are small fuses that blow open during programming. It can only be programmed once and cannot be erased.

 

EPROM (Erasable and Programmable Read Only Memory)

EPROM can be erased by exposing it to ultraviolet light for a period of up to 40 minutes. Typically, an EPROM eraser achieves this function. An electrical charge is trapped in an insulating gate region during programming. The charge is maintained for more than ten years because there is no way for the charge to leak. To annihilate this charge, ultraviolet light is passed through a quartz crystal window (lid). This exposure to ultraviolet light destroys the charge.

 

 

EEPROM is programmed and erased electrically. This memory can be erased and reprogrammed ten thousand times. Both erasing and programming take about 4 to 10 ms (milliseconds). In EEPROM, any location/address can be easily selectively erased and programmed. EEPROMs can erase one byte at a time instead of erasing the entire chip. Therefore, the reprogramming process is flexible but slow.

 

Serial access memory

Sequential access means that the system must search the storage device from the beginning of the memory address until it finds the desired piece of data. A memory device that supports such access is called sequential access memory or serial access memory.

 

Direct access memory

Direct access memory, or random access memory, refers to situations in which the system can directly access the information that the user wants. A memory device that supports such access is called direct access memory. Magnetic disk, optical disk are examples of direct access memory.

 

Cache memory

Cache memory is a very fast semiconductor memory that can speed up the CPU. The cache memory acts as a buffer between the CPU and the main memory. It is used to hold data and program parts that are frequently used by the CPU. Parts of data and programs are transferred by the operating system from disk to cache memory, where the CPU can access them.

 

Supporting memory

Auxiliary memory is much larger in size than main memory but slower. It usually stores system programs, instructions and data files.

 

Computer storage devices

Let's discuss the different types of storage devices available in the market:

 

Primary storage devices

Ram

RAM stands for random access memory that is used to access any temporary data and obtain intermediate results of using that information. It is also known as temporary memory because the data will be stored only as long as the computer system is turned on, if it is turned off the data will be lost.

 

ROM

ROM stands for Read Only Memory. It is also known as non-volatile memory as information is permanently stored here until the user deletes it.

 

Magnetic storage devices

Floppy disk

It is a type of storage device used on a personal basis in a personal computer. Floppy disks are usually made of plastic and protected by using protective cases.

 

Hard disk

It is a hard disk drive (HDD) that uses magnetic storage to store and retrieve data. It is a non-volatile device that stores data that can be changed or deleted countless times.

 

Magnetic disk

It is a card that stores data by changing or reorienting the magnetism of microscopic metal magnetic nanoparticles on the band of the card. Swipe card is another name for it.

 

Flash memory devices

Pen drive

It is also called a USB drive because it has flash memory and a built-in USB interface. These devices can be instantly connected to our desktops and laptops, allowing us to read data into them even faster and more efficiently.

 

SSD

It refers to a solid state drive, a type of mass storage technology similar to hard disk drives. It is more flexible than hard drives because it does not require optical discs.

 

SD card

A contactless smart card is what it's called. It is generally used to store large amounts of information on electronic devices like phones, cameras, etc.

 

Memory card

It is commonly found in digital cameras, printers, gaming consoles and other electronic devices. It can be used to carry a lot of data and comes in different sizes. A memory card reader is required to use the storage device on the computer.

 

Optical storage devices

CD

Compact disc is its name. On the surface of these discs are channels and sections for data storage. It has a round shape and is made of polycarbonate plastic.

 

DVD

Digital Versatile Disc is its name. DVDs are round and flat discs that store data. It is available in two different sizes: 4.7 gigabyte solitary disk and 8.5 gigabyte dual disk.

 

Cloud and virtual storage

Digital or Cloud Storage System This is the modern secondary memory of recent times. We can keep our documents and other objects on the cloud as much as we subscribe to cloud storage.

   

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