2/8 The Floppy Drive

• Roll call

• Video: floppy drive

• Step-by-step lecture

Watch the Video

• Two parts.

1: A floppy disk goes in

• The disk presses against a system of levers.

• One lever opens the shutter to expose the cookie.

lever

shutter

1A: What’s a cookie?

• The cookie is a piece of Mylar (plastic) with a magnetic coating on both sides.

2. The heads are positioned.

• Other levers and gears move the read/write heads into position, almost touching the cookie.

Read/write heads

2A: The read/write heads.

• Electromagnets that can read or write data to the diskette.

3. Controlling movement: spin

• The shaft is run by the drive’s controller board.

• The shaft engages the disk’s hub via the notch to spin it.

shaft

notch in hub

4. Controlling moves: read/write heads

• The controller board runs a stepper motor, which rotates to slide the heads back and forth.

Stepper motor

5. Reading from a diskette

• The diskette has magnetically coded data stored on it.

• Data is binary (1 or 0, on or off, north or south)

5A. Reading from a diskette

• The read/write heads are electromagnets.

• To read, the magnetic signal on the disk influences the core of the head.

corecoil

5B. Reading from a diskette

• The magnetic force creates a slight electric charge that travels up one of the two wires.

5C. Reading from a diskette

• The head moves to the next band. If the polarities match, the resulting bit is a 0. If it is opposite, it is a 1.

0 1

5D. Reading from a diskette

• The next bit always starts with opposite polarity.

0 1

1st bit 2nd bit 3rd bit

0

6. Writing to a diskette: can it be done?

• A diode and light sensor combo checks. If the light can pass, the disk cannot be written to.

• If it is blocked, the disk can be written to.

6A. Writing to a diskette

• Reverse the order to write to a diskette (wire - coil - core - disk ).

6B. Writing to a diskette

• Reverse the order to write to a diskette (wire - coil - core - disk ).

Draw 1001 for a diskette

01 0 11st bit 2nd bit 3rd bit 4th bit