Computer memory is the storage space in computer where data is to be processed and instructions required for processing are stored. The memory is divided into two parts Primary Memory and Secondary Memory.

Primary Memory

Primary memory holds only those data and instructions on which computer is currently working. It has limited capacity and data is lost when power is switched off. Primary Memory are as follows: -

RAM (Random Access Memory): - RAM is the internal memory of the CPU for storing data, program and program result. It is read/write memory which store data until the machine is working. As soon as the machine is switched off, data is erased so it is called as Volatile memory.

Kinds of RAM: -

SRAM (Static RAM)

DRAM (Dynamic RAM)

SRAM: - A type of memory that is faster and less volatile than DRAM, but requires more power and is more expensive. The term static is derived from the fact that it does not need to be refreshed like DRAM

DRAM: - A type of physical memory used in most personal computers. The term dynamic indicates that the memory must be constantly refreshed (reenergized) or it loses its contents. This type of memory is more economical.

ROM (Read Only Memory): - The memory from which we can only read but cannot write on it. This type of memory is non-volatile. The information is stored permanently in such memories during manufacture. A ROM, stores such instructions that are required to start a computer.

Kinds of ROM: -

PROM (Programmable ROM)

EPROM (Erasable Programmable Rom)

EEPROM (Electrically Erasable Programmable Rom)

 

PROM: - PROM is read-only memory that can be modified only once by a user. The user buys a blank PROM and enters the desired contents using a PROM program.

EPROM: - EPROM is a special type of memory that retains its contents until it is exposed to ultraviolet light. The ultraviolet light clears its contents, making it possible to reprogram the memory. To write to and erase an EPROM, you need a special device called a PROM programmer or PROM burner.

 

EEPROM: - EEPROM short for electrically erasable programmable read-only memory. It is programmed and erased electrically. It can be erased and reprogrammed about ten thousand times. 

 Secondary Memory

Secondary memory is where programs and data are kept on a long-term basis. Common secondary storage devices are the hard disk and optical disks. This memory is also known as external memory or non-volatile. It is slower than main memory. Basically there are three types of secondary memory are magnetic, optical and flash devices.

Magnetic Storage Device

Magnetic Tape: - Magnetic tape is the most popular storage medium for large data which are sequentially accessed and processed. The magnetic tape is a plastic ribbon which is usually ½ inch or ¼ inch wide and 50 to 2400 feet long.

 

Floppy Disk: - Floppy disks are primarily used on PCs. Information on a floppy disk is recorded in the magnetized states of particles of iron oxides evenly placed upon concentric circles known as tracks.

Hard Disk: - Hard disks are flat, circular plates made of aluminum or glass and coated with a magnetic material. Hard disks used for personal computers can store up to several gigabytes (billions of bytes) of information. Data are stored on their surfaces in concentric tracks.

Optical Storage Device:

CD (Compact Disk): - Compact disc (CD) is a digital optical disc data storage device. The format was originally developed to store and play only digital audio recordings (CD-DA) but was later adapted for storage of data (CD-ROM). The acquire size of CD is 700 MB.

DVD (Digital Versatile Disk): - DVD ("Digital Versatile Disc" or "Digital Video Disc") is a format that can be used for data storage, including movies with high video and sound quality. DVDs have a storage capacity several times greater than CDs. A DVD reader or writer can usually read CDs. The Size of DVD is 4.7 GB to 17 GB.

BD (Blu-Ray Disk): - A Blu-ray disk (BD) is a high-capacity optical disk medium developed for recording, rewriting and playing back high definition video. It can store large amounts of data and was designed to supersede the DVD. The size of BD is between 25 GB to 50 GB.

Flash Storage Device:

USB Flash Drive – USB flash drive is also known as USB thumb drive; USB stick or Pen drive. It is light weight portable storage device, and it is used as Plug and Play. Now these days, USB flash drive is totally replaced with compact disc, because you can plug it into USB port of the computer system then USB flash drive is capable to store most important files, folders or data.

 

SD Card – SD card is also known as “Secure Digital Memory Card”, and it is part of the flash memory. SD card was designed by Panasonic, Toshiba and SanDisk in 1999 for data storage in the cameras and phones.

 

SSD – SSD stands for “Solid-State Drive”, and it is data storage medium. SSD is a non-volatile memory to store and access any types of data. It does not contain any moving parts, so it delivers the faster access time, noiseless operation, higher reliability, and lower power consumption.