Memory
Like a human brain Computer memory is a storage space which is used to store data and instructions and these data processed as per given instructions. The computer memory is divided into small parts called cells. Each location or cell has a unique address. In memory any data stored in the form of 0 and 1 called bits.
Memory unit
1 byte = 8 bits
1 KB = 1024 bytes
1 MB = 1024 KB
1 GB = 1024 MB
1 TB = 1024 GB
Computer Memory can be divided into three types −
1. Cache Memory
2. Primary Memory
3. Secondary Memory
Cache Memory
Cache memory acts as a buffer memory between RAM and CPU. It is a very high in speed. It temporarily stores instruction and data which is used by the CPU for fast processing. The parts of data and programs are transferred from the disk to cache memory by the operating system, from where the CPU can access them.
|
Advantages |
Disadvantages |
|
Faster than
main memory |
Limited capacity |
|
Less access
time |
Very
expensive |
|
Stores data
for temporary use |
|
Primary Memory (Main Memory)
Primary memory is also known as main memory. It is used to process any instruction as per given input. Primary memory examples are RAM and ROM.
RAM : RANDOM ACCESS MEMORY
ROM : READ ONLY MEMORY
Primary memory lost data when power is off and has a limited capacity. It holds only those data on which computer is working currently. It is made up of semiconductor device. Primary memory is volatile memory and faster than secondary memory. For permanent storage data to be stored in secondary memory.
Secondary Memory
Secondary memory is a permanent storage which is used to save any data for future used. Secondary storage devices are CD, Pen drive, DVD, Magnetic Tape , Hard disk etc. It is also known as external memory. It is movable and can be used for data transfer from one system to other. It is slower in comparison to main memory. Data directly not reached to secondary memory. Firstly data transferred to the main memory after this CPU access it and processed from CPU it stored in secondary memory.
Difference between Primary and Secondary memory
|
Primary
Memory |
Secondary
Memory |
|
Semiconductor
memories |
Magnetic and optical
memories |
|
Volatile
memory |
Non volatile |
|
Data is lost
when switched off |
Data stored permanently |
|
Faster than
secondary memory |
Slower than primary
memory |
|
Computer cannot
run without Primary memory |
Computer can run
without Secondary memory |
RAM
RAM (Random Access Memory) is the internal memory is used to data stored temporarily it means data is lost which power of machine is switched off. RAM is volatile memory and expensive in cost. It is small in size and stored less data.
RAM is of two types −
Static RAM (SRAM)
Dynamic RAM (DRAM)
Static RAM (SRAM)
The static RAM is used as cache memory and very fast. Its cost is higher.
Dynamic RAM (DRAM)
DRAM, unlike SRAM, must be continually refreshed in order 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 as it is cheap and small. All DRAMs are made up of memory cells, which are composed of one capacitor and one transistor.
Difference between SRAM and DRAM
|
Static RAM |
Dynamic
RAM |
|
Faster |
Slower than
SRAM |
|
Used as Cache
memory |
Used as RAM |
|
Larger size |
Smaller in
size |
|
No need to
refresh |
Need to be
refresh continuously |
|
Expensive |
Less
expensive |
|
High power
consumption |
Less power
consumption |
ROM
ROM stands for Read Only Memory. On ROM we can only read but cannot write on it. It is non-volatile memory. It stores data permanently and these data or instructions required to start a computer or for booting process. ROM is also used in other electronic items.
ROM is of following types:
PROM (Programmable Read Only Memory) : PROM is read-only memory can be write only once by any user. It can't be erase or rewrite.
EPROM (Erasable and Programmable Read Only Memory) : EPROM is a read only memory which can be erased and rewritable again with the help of Ultra violet rays.
EEPROM (Electrically Erasable and Programmable Read Only Memory) : EEPROM is a read only memory which can be erased many times and programmed again and again many times electrically. Both erasing and programming take about 4 to 10 millisecond.
Related Questions:
Q. Write units of Computer Memory?
Q. How many types of Computer Memory?