DATABASE MANAGEMENT SYSTEM

Disk and Storage 

Disk 

A disk refers to a data storage device that uses magnetic storage or flash memory to store and retrieve digital information. Disks can be internal or external to a computer and come in various forms, including:

• Hard Disk Drives (HDDs): Use spinning magnetic disks (platters) and a read/write head to access data. They are known for their high storage capacity and relatively low cost, but have slower access times compared to newer technologies.
• Solid State Drives (SSDs): Use flash memory to store data. SSDs have no moving parts, which makes them faster, more durable, and more power-efficient than HDDs, although they are generally more expensive per unit of storage.

Disks are a fundamental component of modern computing systems, providing non-volatile storage, meaning they retain data even when powered off.

Storage

Storage in the context of computing refers to the retention of digital data within a device or system. It encompasses a variety of media and technologies used to store and retrieve data. 

Categories of Storage :

• Primary Storage (Main Memory): Volatile memory that is directly accessible by the CPU. Examples include Random Access Memory (RAM) and cache memory. Primary storage is used for temporary data storage and processing during active tasks.
• Secondary Storage: Non-volatile memory used for long-term data storage. Examples include:
  • Hard Disk Drives (HDDs)
  • Solid State Drives (SSDs)
  • Optical Discs (CDs, DVDs, Blu-rays)
  • Magnetic Tapes
• Tertiary Storage: Often used for backup and archival purposes. Examples include tape libraries and optical jukeboxes, which provide high capacity but slower access times.
• Cloud Storage: Data storage managed by third-party services accessible over the internet. Cloud storage provides scalable and flexible storage solutions, often used for backup, data sharing, and remote access.

Hierarchy of Storage

Cache Memory

Cache memory is a small, high-speed memory located close to the CPU, designed to store copies of frequently accessed data and instructions to speed up their retrieval. 

Characteristics:

Characteristics of Cache Memory

• Speed: Cache memory is the fastest type of memory in a computer system, significantly faster than RAM. It operates at speeds close to the CPU's speed, reducing the time it takes for the CPU to access data.
• Cost: It is more expensive per unit of storage compared to other types of memory like RAM and hard drives.
• Capacity: Cache memory has a relatively small capacity, typically ranging from a few kilobytes (KB) to several megabytes (MB), due to its high cost and fast access speed.

Main Memory (RAM)

Main memory, also known as Random Access Memory (RAM), is a critical component of a computer system. It is a volatile memory used to store data and instructions that the CPU needs while performing tasks. 

Characteristics of Main Memory

• Speed: Main memory is significantly faster than secondary storage devices like hard drives and SSDs but slower than cache memory.
• Cost: Main memory is more expensive per unit of storage compared to secondary storage but cheaper than cache memory.
• Capacity: RAM capacities typically range from a few gigabytes (GB) in consumer devices to hundreds of gigabytes in high-end servers.
• Volatility: Main memory is volatile, meaning it loses its data when the power is turned off.

Flash Memory

Flash memory is a type of non-volatile storage that retains data even when power is turned off. It is widely used in various digital devices due to its combination of high speed, durability, and efficiency.

Characteristics of Flash Memory

• Non-volatile: Retains stored data without requiring a continuous power supply.
• Speed: Faster read and write speeds compared to traditional magnetic storage devices like hard disk drives (HDDs), but generally slower than RAM.
• Durability: No moving parts, making it more durable and resistant to physical shock compared to HDDs.
• Cost: More expensive per unit of storage than HDDs but less expensive than RAM.
• Capacity: Ranges from small capacities in USB drives to large capacities in solid-state drives (SSDs) and enterprise storage solutions.

Magnetic Disk

Magnetic disks are a type of data storage device that uses magnetic storage to record and retrieve digital information. The most common form of magnetic disk is the hard disk drive (HDD), but it also includes other forms like floppy disks and magnetic tape. 

Characteristics of Magnetic Disks

• Non-volatile: Data remains stored even when the device is powered off.
• Speed: Slower than solid-state drives (SSDs) and RAM but faster than magnetic tape.
• Cost: Lower cost per unit of storage compared to SSDs, making it economical for large-scale storage.
• Capacity: Can store large amounts of data, ranging from hundreds of gigabytes (GB) to multiple terabytes (TB).
• Durability: Contains moving parts, making it more susceptible to physical shock and wear over time compared to SSDs.

Optical Disk

Optical disks are data storage devices that use laser technology to read and write data. They are commonly used for media distribution, data storage, and archival purposes. 

Characteristics of Optical Disks

• Non-volatile: Retains data without requiring power.
• Speed: Generally slower than magnetic disks and solid-state drives (SSDs) for data access.
• Cost: Relatively low cost per unit of storage, especially for distribution and archival.
• Capacity: Varies depending on the type of optical disk, typically ranging from 700 MB (CDs) to 50 GB or more (Blu-ray).
• Durability: Resistant to physical shocks but can be damaged by scratches and exposure to sunlight.

Magnetic Tape

Magnetic tape is a type of data storage technology that uses a thin strip of plastic film coated with a magnetic material to store data. It is one of the oldest types of data storage, yet it remains relevant due to its high capacity and cost-effectiveness for certain applications. 

Characteristics of Magnetic Tape

• Non-volatile: Data remains stored without requiring power.
• Speed: Slower access time compared to magnetic disks and SSDs, as it is a sequential access storage medium.
• Cost: Very low cost per unit of storage, making it economical for large-scale storage.
• Capacity: Extremely high capacity, with modern tapes capable of storing several terabytes (TB) of data.
• Durability: Long lifespan and reliable for archival purposes if stored properly, but can be susceptible to environmental conditions like humidity and temperature.

 

Magnetic Disk Pdf