Overview on different disk types and disk interface types

In this article we will try to understand about different disk types and disk interface types available with us.

 

Different Storage Types

The term storage is generic and describes several different storage mechanisms storing data in different ways

  • Electronic
  • Magnetic
  • Optical
  • Mechanical

Now before we start with the overview of different disk types, let us understand few terminologies

 

Drive Access Speed

  • This is the time it takes to locate the data on the drive.
  • The faster the drive rotates, the quicker the drive is able to locate a piece of data

Overview on different disk types and disk interface types

 

Different Disk Types

Below are the different disk types available:

  • Hard Drive (HDD)
  • Solid State Drive (SDD)
  • Optical Disks

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Hard disk drive (HDD)

  • A HDD is a mechanical drive
  • The hard disk drive (HDD) is a secondary storage type. As such, it is a computer component that uses the motor to spin the disc, has a magnetic read-and-write head, and has metal platters that permanently store data. Each platter contains tracks and sectors.
  • The starting point for storing data in HDDs is the outer track.
  • In the case of an HDD with one disc platter, the read-and-write head is located above the platter at a distance of microns, thus never touching the disc. If it does, then physical damage occurs.
  • The data storage capacity is measured in bytes (nowadays it is GB), while the disc spinning speed is measured in rotations per minute (RPM).
  • Most common RPM rates for PCs and laptops are from 5400 RPM to 7200 RPM, while for servers the most common RPM rates are from 10,000 RPM to 15,000 RPM.
  • Usually, the HDD is located inside the computer's case and is mounted in drive bays.
  • However, there are also external HDDs, mainly used for installing the operating system and applications, as well as for storing data.
  • In the event of HDD disposal, it is recommended to perform disk shredding.

 

Solid state drive (SSD)

  • The solid-state drive (SSD) is another storage technology that is considered to be secondary storage.
  • Unlike HDDs, SSDs are memory chips with no moving parts.
  • They use less voltage (5V) than HDDs (12V for spinning the platters), are noiseless, are more physically reliable, and provide faster data access.
  • SSDs are behind HDDs in capacity and cost.
  • However, based on current development trends in storage technologies, things might turn in favor of SSDs over HDDs.
  • These days, many manufacturers offer their PCs and laptops with SSD disks that hold the operating system and applications, as well as HDD disks to be used for data storage.
  • Additionally, SSD drives are also encountered on servers, including NAS and SAN devices too.

 

Optical disks

  • Unlike HDDs that use the electromagnetic field to read and write data from/to disk platters, optical discs utilize laser beams with a specific wavelength to read and write data from/to compact discs (CDs).
  • Always try to differentiate between the optical disk drives (ODDs) and optical discs, such as a CDs or DVDs.
  • The first is the device where the CD or DVD is inserted. CDs contain tracks in the form of a spiral.
  • The starting point for storing data on CDs is the inner track.
  • As is the case with HDDs, optical discs too are measured by capacity in bytes (B).
  • Usually, the capacity of common CDs is between 650 MB and 700 MB, while common DVDs range from 4.7 GB to 8.5 GB.
  • In contrast to HDDs, the speed of optical discs is measured in KB/s and is determined by an x symbol that is equal to 150 KB/s.
  • That said, if your optical drive has a speed of 24x, then its speed is 24 x 150 KB/s = 3600 KB/s = 3.6 MB/s.

There are three recording types of optical disks:

  • CD-ROM and DVD-RAM are read-only optical discs
  • CD-R and DVD-R/DVD+R are write-once optical discs
  • CD-RW and DVD-RW/DVD+RW are rewritable optical discs

The most common forms of optical media at present are DVDs and Blu-ray discs. The latter has been designed to supersede DVD technologies, thus achieving tremendous capacities where a single layer holds 25 GB, a dual-layer holds 50 GB, 100 GB for triple-layer discs, and 128 GB for quadruple-layers.

 

Advantages and Disadvantages of different storage types

Storage technologies are numerous, as there are numerous opportunities too. As such they offer many advantages and disadvantages at the same time. So let us look at some of these devices:

CharacteristicSSDHDD
Startup timeNearly instantaneousSign up can take few seconds
FragmentationVery smallDefragmentation is required for best performance
Temperature controlTolerates high temperatureTemperature should stay below 95 or additional cooling is required
NoiseNearly silentVary between models
Susceptibility to failureExtremely resistant to shocksusceptible to shock and vibrations
Installationnot sensitive to location or positionMust be mounted for various reasons
Reliability and expected lifetimeNot as likely to experience mechanical failurePotential for mechanical failure
Data transfer ratesDelivers consistent read/write speedSlower response time
PowerFlash based on average requires half the power of an HDDAnywhere from 0.35 to 20 watts
CostMore expensiveLess expensive

 

We will also cover different disk interface types which are used today to connect different disk types with the hardware

  • Advanced technology attachment (ATA)
  • Integrated Drive Electronics (IDE)
  • Serial ATA (SATA)
  • Small Computer system interface (SCSI)
  • Serial attached SCSI (SAS)
  • Fibre Channel

 

Different Disk Interface Types

 

IDE and ATA

Now ATA is the interface standard for connecting storage devoice, IDE is the integration of the controller on to the harddrive itself. So the controller is on the card on the bottom of the hard drive. So ATA and IDE are basically synonymous. The Advanced Technology Attachment (ATA), also known as Integrated Drive Electronics (IDE), is a legacy interface that is used to connect hard disk drives, optical disc drives, floppy disk drives, and related storage technologies to computers.

The two most popular types of ATA interface are:

  • Parallel ATA uses a 40-pin connector and cable for data transfer to connect the storage device to the computer's motherboard, and Molex as a power connector to connect the storage device to the computer's power supply. The disk controller resides on a drive itself.
  • Serial ATA represents a replacement for the PATA interface and is used widely in personal computers. It uses a 7-pin cable for data transfer to connect the storage device to the computer's motherboard, and a 15-pin power supply connector to connect the storage device to the computer's power supply. As with PATA, in SATA too the disk controller is located on a drive.

 

SCSI

  • Introduced in 1978
  • It is used heavily in block-level storage systems
  • The server operating system uses the SCSI protocol to read and write data on an SCSI controller that manages storage devices.
  • Designed to run over parallel cables
    • Now running over parallel cables
  • Speeds
    • Initial cable transfer speed of 5MB/second
    • 2003 recent implementation (Ultra 640SCSI) 640MB per second
  • Higher performance than SATA but more expensive
  • The two most popular types of SCSI are SPI and SAS.
  • The SPI is the early version of SCSI, whereas the SAS is the modern version of SCSI that provides high data transfer rates, and is widely used in servers.
  • Internet Small Computer System Interface (iSCSI) places the standard SCSI protocol into an IP packet, thus extending its functionalities throughout the organization's network.

 

Fibre Channel

  • Fibre Channel (FC) is another way of extending the functionalities of the standard SCSI protocol, enabling storage consolidations and longer distances.
  • Fibre Channel over Ethernet (FCoE) does the same for the FC protocol as iSCSI does for the SCSI protocol.
  • FCoE extends the functionalities of the FC protocol across Ethernet networks.

 

References:
Different Disk Types and Advantaeges
Disk Interface Types
Solid State Drive vs Hard Disk Drive

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