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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.
PRIMARY OR MAIN MEMORY
Main memory is divided into two parts :
Random Access memory (RAM), should be better known as Read Write Memory (RWM).
Read Only Memory (ROM) .
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
Read only memory (ROM)
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
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
CLASSIFICATION
MAGNETIC BASED STORAGE DEVICES
Prepared using using formatting
Data is recorded on disk in concentric circular bands calledtracks.
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