Floppy disk drive (FDD) and hard disk drive (HDD)

This post is lesson 33 of 42 in the subject Computer Hardware

This article will discuss the features of two storage devices, the hard drive (HDD) and the floppy drive (FDD). Storage devices usually use to store operating systems, software, and data, also called external memory. These devices are non-volatile, and there are various types available, including the floppy disk, hard drive, SSD, optical disc, and USB.

secondary memory in computer

1. FDD (Floppy Disk Drive)

The FDD has a limited capacity of 2.88 MB, while floppy disks usually only use 1.44 MB of capacity. Floppy drives and disks are not commonly used any more due to their slow access speed and limited capacity.

FDD (Floppy Disk Drive)

FDD Features

  • Size: 3.5”/5.25”
  • Capacity: 720KB, 1.44MB, 2.88MB
  • Connection: cable with 34 pins
  • Rotation speed: 300 RPM

2. HDD (Hard Disk Drive)

HDDs are compact, have fast access speeds, large storage capacities, and are durable. They typically come in sizes of 3.5 inches or 2.5 inches.

HDD (Hard Disk Drive)

2.1. Physical structure of the hard disk drive

The HDD comprises the following components:

  • Chassis
  • Spindle
  • Platter
  • Read/write head
  • Actuator
  • Control circuit
Structure of HDD

The chassis is made of aluminum and plastic materials to protect the HDD components.

The platter is typically made of aluminum, glass, or ceramic substrate with two sides coated in a magnetic and protective layer. It is mounted on the same shaft and consists of many magnetic disks stacked on top of each other.

The read/write head is responsible for reading and writing data, with each side of the platter having its head.

The control circuit transmits data between the mainboard and HDD, controlling read/write operations as well as the rotation speed.

The cache stores temporary data.

The actuator is the motor for rotational movement.

2.2. Logical structure of the hard disk drive

The track is a circular strip of physical data blocks on the platter.

A sector is an element on the track, each sector is 512 bytes in size.

A cylinder is a cylindrical intersection through the stack of platters in a disk, centered around the disk’s spindle.

Landing Zone is the pause position of the read/write head.

A cluster is a collection of sectors. Clusters are allocation units for data on various file systems (FAT, NTFS, etc.), where data mainly consists of files.

Track, cluster, sector in HDD

3. How HDD works

The magnetic disk has a thin layer of magnetic material on its surface. At first, the magnetic particles have no orientation. When the magnetic head passes over them, these particles align themselves directionally.

During the writing process: The electrical signal is sent to the magnetic head. This turns magnetic particles into tiny magnets, with the direction of the magnetic particles determined by whether the input electrical signal is 0 or 1.

During the reading process: The magnetic head moves along tracks on the surface of the magnetic platter and scans the magnetic particles. When the magnetic particles pass under the head, they induce an electric pulse that is interpreted as a 0 or 1 signal.

working principle of HDD

4. HDD specifications

Data Storage Capacity

  • Refers to the amount of data that can be stored on a hard disk drive (HDD).
  • To calculate HDD capacity, multiply the number of bytes per sector by the number of sectors per track, the number of cylinders, and the number of read/write heads.
  • HDD capacity is typically measured in gigabytes (GB) or terabytes (TB) (e.g. 250 GB, 500 GB, 1 TB, etc.).

Rotational Speed

  • Refers to the speed at which the magnetic disk rotates to read and write data.
  • Usually measured in revolutions per minute (RPM) (e.g. 5400rpm, 7200rpm, 10,000rpm, 15,000rpm, etc.).

The cache of an HDD temporarily stores data during the hard drive’s working process. The amount of cache memory in an HDD is typically a few MB (e.g. 4MB, 8MB, 16MB, etc.).

Connections are technical regulations that help connect the HDD and the mainboard. HDD connection standards include:

  • S-ATA
  • SCSI

Refer to the article Storage device connectors on the motherboard to learn the connection standards of the HDD.

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