Computer Memory
The word “memory” in computer system refers to the place where information or data can be stored and later retrieve by the computer system for further processing. It is also be termed as the “brain” of the Computer System.
The units which are used to measure computer memory are as follows:
1 Bit- is the smallest unit of Computer Memory such as 0 or 1
1 byte= 8 bit
1 Kilobyte = 1024 byte = 1 kb
1 Megabyte =1024 kb = 1 mb
1Gigabyte = 1024 mb = 1 gb
1 Terabyte = 1024 gb = 1 tb
1. Primary Memory :-
Primary Memory is also be termed as Main Memory, which is directly connected to the CPU. It stores data that are written by the manufacturer or frequently used by the CPU. It is smaller in size and faster in speed.
The Primary Memory is further classified into two parts, like RAM and ROM.
RAM
RAM also known as “Random Access Memory” it stores the data which are currently being used by the CPU. Data are temporarily stored in RAM, which needs power or electricity to retain its data. It is volatile in nature, as the power goes off its contents are also be removed.
RAM is further classified into two main parts such as-
SRAM- SRAM stands for “Static RAM”, which retains its content as long as the power is supplied to the system. It is volatile in nature and does not needs to be refreshed periodically. It is faster than DRAM and more expensive as well.
DRAM-stands for Dynamic RAM. It also retains data only when electricity is supplied to the system. IT needs to be refreshed periodically to retain its data for which it works slower and also cheaper than SRAM.
ROM
ROM stands for “Read Only Memory” as the name implies it can only read data, which was already stored in it and also non-volatile in nature. It mainly contains BIOS information, which help to boot our computer when we just turn on our computer system. ROM is mainly classified in three types such as-
PROM- stands for “Programmable Read Only Memory”. The data, which was stored in it is permanent in nature as written by manufacturing company only.
EPROM- stands for “Erasable PROM” as the word refers “erasable” means the user can rewrite or erase the data as per requirement. So in EPROM user have the right to rewrite the data with the help of ultra violet rays, it is much expensive than PROM.
EEPROM- stands for “Electrically Erasable PROM” the type of ROM which can erased one byte at any time rather than erasing the entire chip at once by deploying ultraviolet rays in it.
2. Secondary Memory:
Secondary Memory is a type of computer memory where we can store Data, Information, Files and Multimedia Files permanently. So, that it can be retrieved as and when needed. We cannot lose data stored in it when the power goes off, because it is non-volatile in nature.
For accessing data secondary memory uses the following two methods such as-
1. Sequential Access: In this method the desired data can be accessed sequentially or line by line. Example: Magnetic Taps etc.
2. Direct Access: In this method the desired data can be accessed directly by using indexing. Example: Magnetic Disk, Optical Disk etc.
Example of Secondary Memory / Secondary Storage Units:
1. Magnetic Tape: - Magnetic tape is a similar type of plastic tape with magnetic coating on it that is used in music cassettes. It cannot be used to store data, because it uses the sequential access method to read data line by line. It can only store Music, Movie etc.
2. Magnetic Disk: Magnetic Disk is a widely used storage medium in which direct access method being used to store and retrieve data. It is non-volatile in nature; once the data or information is stored it will not be erased even if the power goes off. Hard Disk, Floppy Disk etc are examples of magnetic disk.
CD:
CD stands for “Compact Disk”, is a storage unit with storage capacity is up to 700 MB. It mainly used to store Small Program, Software, music, movies etc. CD can be categorized into following two parts such as-
1. Compact Disk Read/Write (CDR/W)
2. Compact Disk Read Only Memory (CDROM)
DVD:
DVD stands for “Digital Versatile Disk”, is a large storage unit/medium. The storage capacity of this medium is up to 4.7 GB, which is much larger than a CD has. It is also being used to store Large Program, Software, music, movies etc. DVD can be categorized into following two parts such as-
1. Digital Versatile Disk Read/Write (DVDR/W)
2. Digital Versatile Disk Read Only Memory (DVDROM)
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