What is Disk Interface? (Explained)

What is Disk Interface?

A disk interface refers to the specific type of circuit board. This allows a hard drive or a floppy drive to communicate with the host computer.

Ideally, these interfaces can be defined as the physical as well as the logical means to connect the hard disk to the computer system.

KEY TAKEAWAYS

• The hard disk interface typically helps in connecting the drive to the host computer and helps in the process of transferring data between the memory of the former and the cache of the latter.
• The disk interface of the specific type of hard disk determines the rate of transfer between the disk and the computer, and the quality of the interface affects the level of performance of the computer system as a whole.
• The disk interface plays a very important role in the communication of the drive and the computer because with any section on the board failing it will not work and nothing would be possible even if the drive is in a perfect working condition.
• There are different types of disk interfaces available for connecting different types of devices to a computer such as SAS, SCSI, SATA, PATA and more. All these different types come with different features to offer better performance.
• Different disk interfaces have different data transfer speeds and the encoding technique is usually not set by them, though the drive normally uses the Run Length Limited or RLL encoding process.

Understanding Disk Interface

The disk interfaces are the channels to transfer data from the hard disks cache to and from the memory of the computer system.

There are quite a few different varieties of interfaces that can be divided under the broad categories of IDE and SCSI based on their rate of data transmission and technical specifications.

In addition to that, there are also a few early hard disk interfaces such as:

• Storage Module Device or SMD
• Shugart Associates System Interface or SASI
• ST 506 and others from Seagate Technology
• Enhanced Small Disk Interface or ESDI

Historically, there were the serial interfaces. These specific types of earliest interfaces connected the drives to the bus adapter by using only one cable to perform the combined function of data transfer and control.

The older interfaces supported the older hard drives that typically had two ribbon cables to serve two different purposes such as:

• A 20-pin data cable
• A 34-pin control cable

The modern drives, however, come with only one single ribbon cable to serve both the purposes.

Apart from that, the hard disk drive interfaces in the early days were referred to as bit serial data interfaces.

These interfaces usually had two cables to connect the drive to the controller. One of these cables was used for data transfer and the other for control.

However, the contemporary bit serial interfaces use only one cable for data and control to connect the hard disk drives to the bus interface adapter of the host computers.

The data transfer rate and maximum storage capacity supported by some of the disk interfaces are mentioned here.

In the list, you will even find those of the older ones as well. This will help you to make a much better comparison.

• The SATA interface typically supports a data transfer rate ranging between 150 MB/s and 600 MB/s and a maximum storage of up to 20 TB.
• The SAS interface typically supports a data transfer rate ranging between 375 MB/s and 750 MB/s and a maximum storage of up to 12 TB.
• The older PATA interface typically supports a data transfer rate ranging between 3 MB/s and 133 MB/s and a maximum storage of up to 1 TB.
• The SCSI interface typically supports a data transfer rate ranging between 5 MB/s and 320 MB/s and a maximum storage of up to 1 TB.
• The older IPI interface typically supports a data transfer rate ranging between 10 MB/s and 25 MB/s and a maximum storage of up to 3 GB.
• The ESDI interface typically supports a data transfer rate ranging between 1 MB/s and 3 MB/s and a maximum storage of up to 2 GB.
• The SMD interface typically supports a data transfer rate ranging between 1 MB/s and 4 MB/s and a maximum storage of up to 2 GB.
• The ST 506 RLL interface typically supports a data transfer rate of 937 KB/s and a maximum storage of up to 200 MB.
• The ST 506 MFM interface typically supports a data transfer rate of 625 KB/s and a maximum storage of up to 5 MB.

Types of Hard Disk Interface

Typically, there are six major types of hard disk interfaces available such as Parallel ATA or IDE, Serial ATA, SCSI, M.2, SAS, and Fiber Channel.

All these different types of hard disk interfaces have different use cases such as:

• Mostly, IDE is used in the household products, while a few are used in the server sectors.
• Fiber Channel is quite expensive and is used only in high-end and high-performing servers.
• SATA has become mainstream now and most of the desktop computers, notebook computers, and Solid State Drives (SSDs) use it.
• The SAS interface is mostly used in the server computers for its greater reliability and faster data transmission capabilities.

Here is a brief description of each of the major types of hard disk interfaces.

IDE:

Integrated Drive Electronics or IDE hard disk interface integrates the hard disk body and the controller. This particular feature offers significant benefits such as:

• Reducing the length and number of cables
• Increases the reliability of data transfer
• Makes manufacturing hard disks easier

Also known as the first IDE-type hard disk ATA-1, this compatible and cost-effective interface uses three specific transmission modes such as:

• Programmed I/O (PIO)
• Direct Memory Access (DMA)
• Ultra DMA (UDMA)

SCSI:

Small Computer System Interface or SCSI is entirely different from IDE in the sense that it is designed as a high-speed data transmission technology commonly used in minicomputers more than in the hard disks.

Available in three different versions, namely SCSI 1, SCSI 2, and SCSI 3, this specific interface offers the following benefits:

• Wider application range
• Larger bandwidth
• Better multitasking abilities
• Hot swapping ability
• Low rate of CPU occupancy

However, it is expensive and offers little BIOS support, lacks a common SCSI software interface, and needs to be set for each individual computer system. All these features make it a favored option to use in high-end workstations and servers.

Fiber Channel:

It is pretty much the same as SCSI and is usually designed for the network systems, though modern hard disk systems also use it. The benefits offered by this interface include the following:

• Improved data transfer speed
• More flexibility for multi-disk storage systems
• Higher communication speed
• Hot swap
• Faster bandwidth
• Large number of device supported
• Remote connection

The better and improved features of the Fiber Channel make it suitable for use in:

• The servers
• The high-end workstations
• Mass storage sub-networks
• Switches
• Different peripherals for serial and bidirectional data communication through hubs
• Point-to-point connections

The Fiber Channel supports different protocols with a diverse range of services offered such as:

• FC 0
• FC 1
• FC 2
• FC 3
• FC 4

SATA:

Serial Advanced Technology Attachment or SATA interface connects the ATA hard drives to the motherboard of a computer via the serial connection mode and by using an embedded clock signal.

It offers better error correction not just for data but also for the transmission instructions, making it more reliable for data transfer. The features of it include:

• Higher data transfer speed than IDE
• Hot swap support
• Small and thin
• Lower power consumption
• Backward compatibility with PATA
• Master and slave disk jumper setting are not required

SATA is usually available in three versions such as:

• SATA 1.0
• SATA 2.0
• SATA 3.0

M.2:

This new interface specification is designed to replace the mSATA interface and to be used for hard drives in Ultrabooks. These interfaces are usually divided into two specific types such as:

• One that uses the conventional SATA AHCI protocol and is same as regular SATA SSDs and
• One that uses the NVMe protocol providing a transfer speed of 3000 MB/s or more.

SAS:

Serial Attached SCSI or SAS is similar to SATA technology using serial technology. It offers benefits such as:

• Higher transmission speed
• Improved internal space with shorter cables
• Enhanced performance
• More expandability
• Backward compatibility with the SATA

SAS is made up of three specific types of protocols that help in transferring data between different types of devices. These are:

• The serial SCSI protocol (SSP) for transmitting SCSI commands
• The SCSI management protocol (SMP) for maintaining and managing connected devices
• The SATA channel protocol (STP) for transmitting data between SAS and SATA

The SAS backplane can be linked to two ports, one for the high-performance SAS drives and the other for the high-capacity SATA drives. This means, SAS allows both SAS drives and SATA drives to coexist in a storage system at the same time.

Is SAS a Disk Interface?

Serial Attached Small Computer System Interface (SAS) is actually a point-to-point protocol that accesses the peripheral devices of a computer and allows digital transfer one bit at a time through thin cables.

It typically uses the regular SCSI command set and provides voluntary compatibility with different versions of Serial ATA such as version 2 and later.

In other words, SAS allows connecting most of the SATA drives to most of its controllers or backplanes. However, it is not possible to connect SAS drives to SATA backplanes.

Technically, the SAS standard can be defined by its different layers. In the order of highest to lowest, these layers are as follows:

• Application
• Transport
• Port
• Link
• PHY
• Physical

Apart from that, it also follows three specific transport protocols as follows:

• Serial SCSI Protocol (SSP) to allow for command-level communication with the SCSI systems
• Serial ATA Tunneling Protocol (STP) to allow for command-level communication with SATA devices
• Serial Management Protocol (SMP) to allow managing the SAS fabric

So, you can say that the SAS technology is a specific protocol that also acts as an interface for the modern hard drives.

Which Hard Drive Interface is Fastest?

If you compare Parallel Advanced Technology Attachment (PATA) and Serial Advanced Technology Attachment (SATA) hard drives, the latter is much faster than the former.

It can write with a throughput of about 600 MB/s to the disk with an interface rate of about 6 GB/s.

However, the SAS interface is even faster in data transmission, clocking between 375 MB/s and 750 MB/s.

Conclusion

The hard disk interface connects the host computer system to the hard disk.

The primary function of it is to act as a conduit for transmitting data between the memory of the host computer system and the cache of the hard disk.

Ideally, the speed of data transfer is determined by the type of the hard disk interface.