Dynamic Random-Access Memory (DRAM) – Dynamic memory must be constantly refreshed, or it
loses its contents. This type of memory is more economical.
Static Random-Access Memory – SRAM is faster and less volatile than DRAM but requires more power
and is more expensive. It does not need to be refreshed like a DRAM.
Synchronous Dynamic Random-Access Memory - A type of DRAM that can run at much higher clock
speeds.
ROM (Read Only Memory) - ROM stores data permanently on personal computers (PCs) and other
electronic devices. It performs major input/output tasks and holds programs or software instructions.
It
is non-volatile.
MROM (Masked ROM) - The very first ROMs were hard-wired devices that contained a pre-
programmed
set of data or instructions. These kinds of ROMs are known as masked ROMs which are inexpensive.
PROM (Programmable Read Only Memory) - PROM can be modified only once by a user. The user can
buy a blank PROM and enter the desired contents using a PROM program.
EPROM (Erasable and Programmable Read Only Memory) - The EPROM can be erased by exposing it
to
ultra-violet light. EPROMs have a Quartz window in the package to expose the chip to UV light. They
were widely used as the BIOS (Basic Input Output System) chips in computer motherboards.
EEPROM (Electrically Erasable and Programmable Read Only Memory) - The EEPROM is programmed
and erased electrically. It can be erased and reprogrammed about ten thousand times. Both erasing
and programming take about 4 to 10 milliseconds. They were also used as BIOS chips.
Secondary Memory
Secondary memory stores data on a long-term basis. It cannot be processed directly by the CPU. It
must first be copied into primary storage. Secondary memory devices include magnetic disks like hard
drives and floppy disks, optical disks such as CDs and CDROMs, and magnetic tapes, USB Flash drives.
Hard drive – It is a non-removable storage device containing magnetic disks or platters rotating at
high
speeds. The hard drives store data in segments of concentric circles. It may spin at 5,400 to 15,000
RPM.
Floppy Disk - Floppy disk is composed of a thin, flexible magnetic disk sealed in a square plastic
carrier.
Floppy disks were widely used to distribute software, transfer files, and create backup copies of data.
To
read and write data from a floppy disk, a computer system must have a floppy disk drive (FDD).
Compact Disc (CD) - A compact disc is a portable storage medium that can be used to record, store
data in digital form. They are fragile and prone to scratches.
Compact disc read-only memory (CD-ROM) - It is a storage device that can be read but can’t change or
delete it.
Digital Video Disc (DVD) - A device currently used to store data in large amounts and accepts high
definition material. A two-layered DVD can hold approximately 17 gigabytes of video, sound, or other
data.
Blue-ray Disc – The upgraded version of CD and DVD discs and drives are the Blu-ray discs. It is
commonly known as BD-ROM. The Maximum capacity of BD disc is 25GB if single layer and 50 GB if
dual layer.
Holographic Versatile Disc (HVD) – It is a holographic storage format and has a maximum capacity of
3.9 terabytes.
Flash Drives – Flash drives are small, ultra-portable storage device. They connect to computers and
other devices via a built-in USB plug. They are often referred to as pen drives, thumb drives, or jump
drives. Mostly they have a storage capacity from 8 GB to 64 GB.
Zip Disks – An advanced version of the floppy disk is known as Zip Disks. It was developed by Iomega.
Zip disks are available in 100 and 250-MB and 750 MB capacities and they are used to store, share and
back up large amounts of data.
Cache Memory - It is a very high-speed semiconductor memory which can speed up the CPU. It acts as
a buffer between the CPU and main memory. Example: Registers
Virtual Memory - Virtual memory permits software to use additional memory by utilizing the hard disk
drive (HDD) as temporary storage.
