• 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

• Reused

• Reside in a protective case

Storage Organisation of magnetic disk

• Tracks and sectors

• Double-sided disks

• Sector number, track number and surfacenumber

• Cluster

• Disk pack and Cylinder

• Accessing data– Seek, Rotate, Data transfer

Types of Magnetic disk

• Floppy Disk

•Hard Disk

• Zip Disk

Advantages of Magnetic Disk

• Direct access

• Online and offline storage

• Movable

• Data transfer rate

• High data recording densities

Disadvantages

• Dust free environment

• Costlier

Optical Disk

Advantages

• Large capacity

• Life span

• Not affected by magnetic field

• Portable

Disadvantages

• Costlier

• Needs both hardware and software forwriting

• More complicated