Magnetic Bubble Memories

MAGNETIC BUBBLE MEMORIES

It is a new technique which can store million bits of data in a single IC package. Magnetic bubble is a direct access storage medium. Magnetic bubbles are soft magnetic materials with magnetic domains of a few μm in diameter.

Construction

Bubble memory consists of materials such as magnetic Garnets and store the data as microscopic magnets. A thin film of these Garnets are deposited on a non‒magnetic substrate which is made up of Gadolinium Gallium Garnet (GGG) constitutes a bubble memory chip.

When a magnetic field is applied to such a chip (i.e.,) by placing it inbetween two permanent magnets, the magnetic domains contracts and finally forms a small cylindrical domain area which is called as magnetic bubble as shown in Fig. 1.29.

These bubbles constitute a magnetic region of one polarity (either North or South) surrounded by the magnetic region of opposite polarity.

The information is represented as the presence or absence of a bubble at specified location. The bubble position remains unchanged even in the absence of electrical power. These bubbles can be moved electronically through the access lines at very high speeds and hence the access time and storing time is very less in this type of memories.

Here the presence of bubble represents the logic '1' and the absence of bubble represents the logic '0'. Thus the data may be represented in bubble storage by the presence (or) absence of bubbles.

The schematic diagram of a magnetic bubble memory is as shown in Fig. 1.30. It consists of one major loop and 157 minor loops which are arranged from right to left. Each minor loop has 641 bubble sites. Thousands of coded characters may be stored in a single chip.

Writing Operation

When a data has to be stored, the bubbles from the minor loops are transferred to major loop and it goes to write station. In write station the message is entered and the bubble site again comes to minor loop.

Reading Operation

To read the data from the storage, the bubble from minor loops are transferred to major loop and it goes to read station, then it comes to minor loop. The data can be altered by the erase station, if we need to erase it.

Special features

1. It is Non‒volatile.

2. It has high storage capacity than magnetic hard disk.

3. It has high access speed.

4. It has storage even in the absence of electrical power.

5. Bubble sites are moved electronically.