External Storage Systems: Types, Structure, and Functionality

Posted on Jan 9, 2025 in Technology

External Storage Systems

Definition

External storage systems, also known as peripheral units or devices, facilitate communication between the CPU and the external world. They serve as mass storage systems or auxiliary means capable of storing information permanently and retrieving it automatically.

Structure

External storage systems consist of two main parts:

  • Mechanical Part: Composed of electromechanical devices controlled by mechanical elements.
  • Electronic Part: Interprets orders from the CPU, handles data reception and transmission, and generates control signals.

Types

Given the Technology

  • Magnetic Technology: Applies magnetic fields to specific materials, causing their particles to react and represent data through their positions.
  • Optical Technology: Employs a laser to read or write microscopic holes on a disc’s surface. Optical devices are known for their reliability.
  • Magneto-Optical Technology: Uses a laser, a magnetic field, and a photodetector to record data. Magneto-optical disks are highly reliable and durable due to a special material that can only be magnetized at high temperatures (150 degrees Celsius), making them resistant to normal temperature fluctuations.

Given the Way They Store Information

  • Reusable: The same storage medium can be used multiple times.
  • Non-Reusable: Once information is recorded, it cannot be changed.

Given Access to Information

  • Sequential: To access specific data, all preceding data must be read or written.
  • Direct: Any data can be accessed almost immediately.

Given the Location of the System

  • Internal: The reader/recorder unit is located inside the computer case.
  • External: The reader/writer drive is located outside the computer.

Given the Connection Between the Support and Drive Reader/Writer

  • Removable: The storage medium can be changed within the reader/writer drive.
  • Non-Removable: The storage medium and the reader/writer drive are permanently united.

Signal Encoders

  1. RZ (Return to Zero)
  2. RS (Return to Saturation)
  3. BRZ (Bipolar Return to Zero)
  4. NRZ (Non-Return to Zero)
  5. NRZI (Non-Return to Zero Inverted)
  6. PE (Phase Encoding)

Types of Formatting

  • Physical or Low-Level Format: Involves tracing tracks and magnetic signals or sectors.
  • High-Level or Logical Formatting: Organizes sectors for use by the operating system.

Master Boot Record (MBR)

The master boot sector, the first sector of a hard drive, contains information about the disk’s logical structure. It includes a small boot program and the partition table. The MBR is 512 bytes long, divided as follows:

  • 2 bytes for the bootable drive signature.
  • 64 bytes for the partition table.
  • 446 bytes for the bootloader.

Partitions

Partitions are divisions within a physical drive, creating logical drives. A single physical unit can be divided into multiple logical units. There are two main types of partitions:

  • Primary: These partitions can contain an operating system and can be designated as active. The active partition is the one from which the boot process begins. A hard disk can have up to four primary partitions.
  • Extended: This partition holds one of the four possible entries in the partition table. Within an extended partition, an unlimited number of logical partitions can be defined.

Hard Drives

The hard drive is an essential component of a computer, capable of storing large amounts of information required by modern applications. Physically, a hard disk consists of several platters stacked and connected by a shaft within an enclosure.