Storage Units and RAM: Structure and Operation

Storage Units: Definition and Types

Item 10: Storage units are those that can permanently store data or programs. They allow modification and re-saving of data for later retrieval. Central microcomputer equipment always includes a hard disk drive and a CD drive. The IDE interface for hard disks and CD/DVD drives is the most commonly used. Motherboards typically have two connectors to connect up to four devices. The SCI interface, used in professional equipment, is currently seeing less use due to the steady growth in flash drive storage capacity.

Physical and Logical Structure of Storage

Storage structure is divided into two parts:

• Physical Structure: This refers to how the storage medium is divided and corresponds to where the information is saved.
• Logical Structure: This is the way information is stored on the media.

Key components of the logical structure include:

• FAT (File Allocation Table): Indicates the position of each of the minimum space approaches used to store information.
• Root Directory: Stores all data, other data files, and folders.
• File Area: Used for storing user files, occupying approximately 98% of the total drive space.

Physical Structure of a Disk

A disk is formed by a plastic material coated with a magnetic plate. Data is stored on the disk in concentric circles called tracks. Each track is divided into sectors of 512 bytes.

Hard Drive (HDD)

The hard drive is the computer's main storage unit, where large amounts of data and programs are permanently kept. Hard drives contain at least two disks stacked on a central axis and isolated from the outside. These disks rotate at a speed of 9600 RPM (revolutions per minute). At the bottom of the disk is a circuit board that translates commands into voltage variations. These variations force the movement of the read/write heads across the surface of the disks.

Hard Disk Physical Structure Details

A hard disk's physical structure consists of a series of disks or plates stacked on top of each other within a housing. A faceplate may contain specific information used for the positioning of the heads. All read/write heads move together, making it faster to write on the tracks of multiple dishes. The tracks are divided into sectors; the number of sectors per track is variable. The read/write head floats above the disk surface, without physical contact. Hard drives are hermetically protected and should not be opened to prevent particle contamination. When the disk is in operation, the head should *not* rest on the magnetic surface.

The operations carried out by the read/write head are:

• Data Writing: Data is written to the disk surface through a stream sent to the electromagnet in the read/write head. This modifies the surface of the disk. When the disk is blank, there are no magnetic peculiarities.
• Data Reading: Reading is based on the inverse process. A variation of the magnetic field in the vicinity of the electromagnet causes the appearance of a power at the same winding. The winding will indicate a 0 or 1 bit depending on the magnetic field.

RAM Operation

Item 9: RAM (Random Access Memory) operation consists of thousands of cells capable of housing an electrical charge. Each of these cells represents 1 bit or binary digit (1 for charged, 0 for no-load). An electronic circuit, called the memory controller, stores and reads the information. The memory controller uses RAS (Row Address Strobe) signals to access any cell and store or retrieve its value. The memory controller contains the memory addresses of all data and controls refresh cycles and data acquisition.

Read and Write Process in RAM

• Reading: The memory controller indicates the position to access by sending electrical charges. This discharges the capacitor and provides the information.
• Writing: The controller indicates where to record and applies voltage. A pulse charges the capacitor.

Types of RAM

• SRAM (Static RAM): A very fast memory typically used for cache.
• DRAM (Dynamic RAM): Slower than SRAM, DRAM uses capacitors to store charge in each cell. These capacitors discharge naturally and need to be recharged periodically.