subject: Memory Representation [print this page] Memory Representation Memory Representation
Bit
Byte
Kilobyte
Megabyte
Gigabyte
Terabyte
RAM (Random Access Memory)
Hard Disk
Main Memory CPU
Types of RAM
SRAM (Static)
- volatile memory
- used as cache memory
DRAM (Dynamic)
- unstable
- needs refreshing
Difference between SRAM and DRAM
Data life
No. of chips
Speed
Cost
Heat production
Latency ROM (Read Only Memory)
Types
Masked ROM
Contains preprogrammed set of instructions
PROM
One-time programmable
EPROM
Erasable by ultraviolet light
EEPROM
Electrically erasable by applying small voltage
Flash ROM
Flash memory written in block sizes
Difference between ROM and
RAM
Volatility
Lifetime of contents
Cost
Storage capacity
Processing Speed
Programs?
RAM, ROM and CPU Interaction
1. Switch on ctr.
2. Loads data from ROM
3. Loads BIOS from ROM
4. Loads OS from hard disk into RAM.
5. Loads application into RAM.
6. After saving flush out the RAM.
Cache Memory
CPU Cache Memory Primary Memory Secondary Memory
Virtual Memory
It is a system memory that is simulated by the hard drive. When all the RAM is being used the computer will swap data to the hard drive and back to give the impression that there is slightly more memory.
Secondary Storage Devices
Magnetic Tapes
Magnetic Disk Optical Disk Magneto
Optical Disk
Floppy Disk
Hard Disk
Zip Disk
CD-ROM WORM
Sequential Access
Data
Data
Data
Data
Data
Data
Data
Data
Magnetic Tape
Plastic tape with magnetic coating
Magnetised and de-magnetised
Different sizes
Can be reused
Sequential access
Frames and tracks
Magnetic tape organization
Advantages
Non-volatile memory
High data recording density
Easily transportable
Disadvantages
Need dust free environment
Slow data access
Difficult to recover
Direct Access
Data
Data
Data
Data
Data
Data
Data
Data
Magnetic Disk
Plastic/metal circular plate/platter coated
with magnetic oxide layer.
1 and 0
Magnetised data converted into electrical pulses for reading and vice versa for writing
