Disk Storage and Hard Disk Systems

• Information needs to be stored somewhere to be easily accessible and retrievable.

Common Disks

• Computers use various types of electronic information requiring storage, including data, application, and configuration files.
• Common types of disks include:
  • IDE disk systems
  • Small Computer Systems Interface (SCSI)
  • SATA disk systems
  • Flash drives
  • Solid State Drives (SSD)

Hard Disk System

• The hard disk system contains three critical components: the controller, the hard disk, and the host adapter.
• Each platter is divided into circles where data is stored; each circle is called a track.
• One platter can have tens of thousands of tracks.
• Tracks are divided into sectors for accurate data location; each sector contains 512 bytes of data.

Hard Disk Components

• The controller sends signals to the various motors and receives signals from the sensors inside the drive.
• The hard disk stores information on small disks stacked together in an enclosure.
• The host adapter translates signals between the hard drive/controller and the computer.

Cassette Tapes vs Hard Disks

• Tapes have to fast-forward or reverse to find data.
• Tapes use recording material coated on a thin plastic strip.
• Tapes have a read/write head that touches the tape directly.
• Tapes move over the head at about 5.08 cm per second.
• Hard disks have recording material layered onto a high-precision aluminum or glass disk.
• Hard disks can move to any point on the surface of the disk almost instantly.
• Hard disks have a read/write head that "flies" over the disk, never actually touching it.
• Hard disks can spin underneath its head at speeds up to 273 km/h.

Hard Disk Capacity

• A file is a named collection of bytes, representing ASCII codes for text or pixel colors for images.
• A typical desktop computer can have between 128GB and 1TB stored as files on SATA or SSD drives.

Hard Disk Performance

• Data rate measures the number of bytes per second the drive can deliver to the CPU, with common rates between 5 and 40 megabytes per second.
• Seek time measures the amount of time between when the CPU requests a file and when the first byte of the file is sent to the CPU, with common times between 10 and 20 milliseconds.

Hard Disk Technologies

• IDE (AT Attachment interface or ATA) has the controller on the drive and uses a short cable to connect the drive/controller to the system.
• EIDE (Enhanced IDE) decreases signal loss, increasing reliability and making the drive easier to install, supporting drives of several gigabytes with data transfer rates greater than 10Mbps.
• Ultra ATA/66 uses a regular IDE cable with extra wires to prevent line noise, achieving a maximum burst transfer rate of 66MB/s.

Serial ATA (SATA) Hard Disks

• SATA offers increased data transfer rates (150/300/600 MBs/second).
• SATA allows for easy cable management and a cable length of up to 3.3 feet (1 meter).
• SATA cables are smaller than PATA (IDE) cables, allowing for increased airflow.
• A computer motherboard has four to six SATA connections.
• SATA provides faster data transfer speeds, more bandwidth, more potential for speed increases in future generations, and better data integrity.

Solid State Drives (SSD)

• SSDs store data on chips, similar to flash drives.
• SSDs contain no moving parts, use less electricity, operate silently, are more resistant to physical shock, and have lower latency than traditional hard drives.
• Latency is the delay before a transfer of data begins following an instruction.

Hard Disk Partitions

• Primary partitions: Partitions on which an operating system can be installed.
• Extended partitions: Can be divided into additional logical drives and do not need assigned drive letters/file systems.
• Hard drives can only have up to 4 partitions.
• File systems control how data is stored and retrieved, marking where one piece of data stops and the next begins.

File Systems

• NT File System (NTFS), also called the New Technology File System, is used by Windows NT operating systems for efficient storage, organization, and file retrieval.
• FAT32 is a disk format or filing system that organizes files on a disk drive, marking the drive into addressable sectors and creating a File Allocation Table (FAT) to locate file information.

Optical Disk Drives

• 1st Generation: Used to store music and computer software.
• 2nd Generation: Used for storing large amounts of data, including broadcast-quality digital video.
• 3rd Generation: Includes Blu-ray disks and supports high-definition video (up to 4K) with greater data storage capacities.
• 4th Generation: Formats such as Holographic Versatile Disc, LS-R, and Protein-coated disc are in development, potentially holding more than 1TB.