Information about Memory types

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INTRODUCTION
In computing memory refers to the physical devices used to store
programs (sequences of instructions) or data (e.g. program state
information) on a temporary or permanent basis for use in a
computer or other digital electronic device.
TYPES OF MEMORIES
Primary or Main Memory
Main memory is divided into two parts :
Random Access memory (RAM), (Read
Write Memory (RWM)).
Read Only Memory (ROM) .

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Random Access Memory (RAM)
A RAM memory chip is an
integrated circuit (IC) made of
millions of transistors and
capacitors. In the most common
form of computer memory,
dynamic random access
memory (DRAM), a transistor
and a capacitor are combines to
create a memory cell, which
represents a single bit of data.
TYPES OF RAM
STATIC RAM
Semi conductor memory
Uses flip flop to store each bit of memory so does not need to be
periodically refreshed
Fast and consumes low power
Expensive and has complex structure(6 transistors) so not used
for high capacity applications
DYNAMIC RAM
Stores each bit of memory in capacitor in an intrgrated circuit
Real capacitors leak charge so capacitors need to be refreshed
periodically
Simple structure (1 capacitor and 1 transistor per bit) so it has very
high density
READ ONLY MEMORY (ROM)
New contents cannot be added
Used to store the instructions of routine type,permanent in
nature and used to control or supervise the hardware
Types Of ROM
Programmable Read Only Memory (PROM)
Programmed to record the information using a facility PROM
– programmmer
Once the information is recorded it cannot be changed

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Erasable Programmable Read Only Memory (EPROM)
Information can be erased and chip can be reprogrammed
to record different information using PROM programmer
In formation is erased using UV radiations
It is of two types- Ultra Voilet Erasable Programmable Read
Only Memory (UEPROM) and Electrically Alterable
Programmable Read Only Memory (EAPROM)
Electrically Erasable Programmable Read Only Memory
(EEPROM)
Memory is erased by electrical signals
Provides easy means to store temporary or permanent
information in the form of ROM memory
Cache Memory
Faster and expensive than RAM
It improves the computer’s performance and is less than 512 KB
Processor can use it to store frequently accessed data and programs instructions
It is of two types – L1 / primary cache(inside microprocessor) and L2/
secondary cache(in the mother board or near the microprocessor)
Secondary Memory
It supplements the main memory. It is permanent memory.
Programs, data entered into the system, intermediate results
and final results produced are stored in the secondary
memory

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Classification of Memories
Magnetic Based Storage Devices
Prepared using formatting
Data is recorded on disk in
concentric circular bands called
tracks.
MAGNETIC TAPE
FLOPPY DISK
HARD DISK
Optical Storage Media
Stores large amount of data in some
formats as much as the entire hard disk
Reads data by focusing a laser- generated
beam of light on light on disc’s surface
CD- ROM discs
DVD- ROM discs
Memory Hierarchy
Ranking of computer memory
devices, with devices having the
fastest access time at the top of
hierarchy, and devices with slower
access time but larger capacity and
lower cost at lower levels
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