3. Primary Memory
• It is the only memory that is directly
accessible to CPU. The CPU
continuously reads instructions stored
there and executes them as required.
• Various "Primary storage devices" are:
• RAM
• ROM
• Cache Memory
4. RAM(Random Access
Memory)
• Random Access Memory allows stored
data to be accessed directly in any
random order. It is a Volatile Memory
i e the data vanishes when the power
supply is cut off.
• These are of 2 types:
SRAM
DRAM
5. DRAM
(Dynamic random access memory)
• This is a Random Access Memory that stores
each bit of data in a separate capacitor. The
capacitor can be either charged or discharged;
these two states are taken to represent the two
values of bit, that are 0 and 1.
• This memory needs to be refreshed periodically
6. SRAM
(Static Random Access
Memory)
• It is faster than the DRAM as it uses a six transistor
configuration. In this the direction of current depicts
the value 0 or 1.
• It is expensive than DRAM
• This memory need not to be refreshed frequently.
7. ROM(Read Only Memory)
• The DATA stored in Read Only Memory cannot be
modified or can be modified only slowly or with
difficulty.
• It is non-volatile memory i e it does not loose data
when the power is cut off.
• Its various types are :
PROM
EPROM
EEPROM
8. PROM
(Programmable Read Only Memory)
• On Programmable Read Only Memory the Data
can be written only once.
• It is Manufactured as a blank memory and then
the data is written on it ,also called as Burning
the PROM.
9. EPROM
(Erasable Programmable read
Only Memory)
It is a special type of ROM that retains its
contents until it is exposed to ultraviolet light.
The ultraviolet light clears its contents ,
makes it possible to reprogram the memory.
10. EEPROM
(Electrically Erasable Programmable
Read Only Memory)
• EEPROM is a special type of PROM that can be
erased by exposing it to an electric charge. Like
other RAM it retains its memory even if the power
is switched off.
• Data is written or erased one byte at a time
11. Flash Memory
Flash Memory is a special type of EEPROM
that can be erased and reprogrammed in
blocks instead of one byte at a time. Many
modern PC's have their BIOS stored on a
flash memory chip so that it can be easily
updated if necessary.
12. Secondary Memory
• Secondary storage does not lose the data
when the device is powered down—it is non-
volatile. Per unit, it is typically also an order
of magnitude less expensive than primary
storage.
• Two Types of secondary storage devices are:
Magnetic storage devices
Optical storage devices
14. Optical storage
devices
Various Optical storage devices are :
•Compact disk Read Only Memory
(CD-ROM)
•Digital Video Disk Read Only Memory (DVD-
ROM)
•CD-Recordable(CD-R)
•CD-Rewritable(CD-RW)
15. Memory is used in
• Computer
• Mobile
• Printer
• Digital Camera
• CD/DVD Players
• Many other appliances like TV,
Washing machine, Digital Diaries etc.
