By Jesisha Jayarajan

M.E Electronics

A magnetic storage device is any device that use the principles of magnetism to store data.

DEFINITION

Magnetic Hard Disks

Magnetic Floppy Disks

Magnetic Tapes

TYPES OF MAGNETIC STORAGE DEVICES

MAGNETIC DISKS

• Removable disk drives and fixed disk drives

• Moving head and fixed head disk drive

• Single head assembly and dual head assembly

• Winchester and non-winchester disk drive

• Open loop and closed loop disk drive

TYPES OF MAGNETIC DISK DRIVES

PRINCIPLE OF MAGNETISM

Oersted’s Law States That:

As an electric current flows through a conductor (wire), a magnetic field is generated around the conductor

Oersted found that, for a straight wire carrying a steady (DC) current

The magnetic field lines encircle the current-carrying wire

The magnetic field lines lie in a plane perpendicular to the wire

If the direction of the current is reversed, the direction of the magnetic field reverses.

The strength of the field is directly proportional to the magnitude of the current.

The strength of the field at any point is inversely proportional to the distance of the point from the wire.

When recording, the head changes electrical impulses to magnetic fields

WRITING TO DISK

A MAGNETIC READ/WRITE HEAD

Faraday found that if a conductor is passed through a moving magnetic field, an electrical current is generated.

As the polarity of the magnetic field changes, so does the direction of the electric current’s flow

FARADAY’S LAW OF INDUCTION

During the read process, a head does not generate exactly the same signal that was written.

Instead, the head generates a voltage pulse or spike only when it crosses a flux transition

DISK READ

MAGNETIC READ WRITE PROCESS

Seek Time:

The time for positioning the head on track is known as the seek time. It increases with the distance.

Rotational Delay:

The time it takes for beginning of sector to reach the head is known as rotational time

DISK PERFORMANCE PARAMETER

Access Time:

The time it take to get into position to read or write is called access time.

Transfer Time:

It is the rate at which the data can be retrieve from or store into the disk platters.

MAGNETIC TAPE

What is magnetic tape?

• Thin layer of material capable of storing a magnetic signal

• Usually contains Iron Oxide

• Inexpensive to store large amounts of information.• A reel of tape could store as much as 225 MB in the early 1980s.

• No other storage technology could compare to the price of tape

• Sequential access – Slow access

Pros and Cons of Magnetic Tape

• Tapes are highly susceptible to magnetic fields and changes in temperature and humidity

• Tapes are also susceptible to physical damage

• Tape miss-feeds

• Magnetic particle instabilities

• Substrate deformation

MAGNETIC FLOPPY DISKS

Floppy disks are the handy devices. And it is convenient to use floppy disks when we want to move data from one place to other place.

A floppy diskette is an ultra thin plastic (Mylar) piece in circular shape.

The name floppy is used since the thickness of the disk is only a few thousand of an inch. The disk is coated with a magnetic material and enclosed in a protective jacket.

• When you use a PC, you need some place to keep your programs and your data files, and that place is your hard disk.

• The hard disk drive has been a very effective storage device since 5 decades in the computer generation era. The first hard disk was invented by IBM in 1956.

HARD DISKS

•Due to their non - volatile nature and random access data storage and retrieval method, hard disk is the predominant device for computer.

THANK YOU