Computer Memory

»  Memory is an essential component of any digital computer. It is storing device. It stores programs and data, which is required by the CPU, and the results generated after processing.
»  The data is stored in the memory unit of CPU.
»  The data storage is in binary digits 0 & 1
»  Following are the unites of Memory
ü 1 Bit = 0 or 1
ü 8 Bits = 1 Byte 
ü 1024 Byte = 1 Kilobyte (KB) (1 to 3 digits)
ü 1024 Kilobyte = 1 Megabyte (MB) (4 to 6 digits)
ü 1024 Megabyte  =  1 Gigabyte (GB) (7 to 9 digits)
ü 1024 Gigabyte = 1 Terabyte (TB) (10 to 12 digits)
ü 1024 Terabyte = 1 Petabyte (PB) (13 to 15 digits)
ü 1024 Petabyte = 1 Exabyte (EB) (16 to 18 digits)
ü 1024 Exabyte = 1 Zetabyte (ZB) (19 to 21 digits)
ü 1024 Zetabyte = 1 Yottabyte (YB) (25 to 27 digits)
»  Memory is primarily of three types
1.  Cache Memory
2. Primary Memory/Main Memory [RAM & ROM]
3. Secondary Memory

Types of Computer Memory

Cache Memory

»  A small high speed memory, which is used to increase the speed of processing by making current programs and data available to the CPU at a rapid rate.
»  The function of the cache memory is to speed up the main memory data access (performance increasing) and most important, in multiprocessor systems with shared memory, to reduce the system bus and main memory traffic that is one of the major bottleneck of these systems.
»  Cache memory makes use of the fast technology SRAM (static random-access memory cells), against a slower main memory DRAM (dynamic random-access memory), connected directly to the processor(s).
»  Cache memory has limited capacity.
»  It is very expensive.

Primary Memory (or) Main Memory

»  Primary memory holds only those data and instructions on which computer is currently working.
»  It has limited capacity and data is usually 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 reside in main memory.
»  It is divided into two subcategories RAM and ROM.
»  Random Access Memory (RAM) - is a type of volatile memory that is stores information on an integrated circuit which hold the data mainly when the program is beaing executed by the CPU. As it is volatile in nature so it cann't store data permanently.
»  Read Only Memory (ROM) - a non-volatile memory chip in which data are stored permanently, and cannot be altered by the programmer.

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.
»  Examples of secondary memory are : disk, CD-ROM, DVD etc.

Memories can also be classified as Volatile Memory & Non-Volatile Memory
»  Volatile memory, is computer memory that requires power to maintain the stored information; it retains its contents while powered on but when the power is interrupted the stored data is immediately lost. Volatile memory has several uses, for example as a RAM drive.
»  Non-volatile memory is memory that does not require a connection to a power source to retain information. In other words, when the power source to which the memory is connected is shut off, the memory does not lose the information it has. Common examples of non-volatile memory are computer hard-disk drives

Frequently asked:
What is the function of the memory?
The computer memory is a temporary storage area. It holds the data and instructions that the Central Processing Unit (CPU) needs. Before a program can be run, the program is loaded from some storage medium into the memory. This allows the CPU direct access to the program.
How many types of memory are used in a computer?
There are two main kinds of semiconductor memory, volatile and non-volatile. Examples of non-volatile memory are flash memory (used as secondary memory) and ROM, PROM, EPROM and EEPROM memory (used for storing firmware such as BIOS). Examples of volatile memory are primary storage, which is typically dynamic random-access memory
What is RAM memory and what does it do?
Other than the specific applications that hog your RAM, if you think bumping your RAM from 3GB to 8GB is going to increase the speed of a regular application-like a video game—you should think again. The only thing that additional RAM does is allow your computer to do more things at once, not actually make it faster
What is the difference between volatile and nonvolatile memory?
Volatile memory requires a constant power supply to retain data whereas non-volatile memory does not require a constant power supply to retain data.


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