Technology

Types of Computer Hard Disk Drives Explained

What Are the Main Types of Computer Hard Disk Drives?

Computers rely on hard disk drives (HDDs) to store data permanently. They are storage devices used to save and retrieve digital information that will be required for future reference.

Hard drives are non-volatile, meaning that they retain data even when they do not have power. The information stored remains safe and intact unless the hard drive is destroyed or interfered with.

The information is stored or retrieved in a random-access manner as opposed to sequential access. This implies that blocks of data can be accessed at any time they are required without going through other data blocks.

Currently, we can group hard drives into five types:

Parallel Advanced Technology Attachment (PATA)
Serial ATA (SATA)
Small Computer System Interface (SCSI)
Solid State Drives (SSD)
NVM Express

Hard Disk Drives Have Stood the Test of Time

Hard disk drives were introduced in 1956 by IBM. At the time, they were being used with general-purpose mainframes and minicomputers. Like other electronic devices, these have witnessed numerous technological advancements over the years. This is in terms of capacity, size, shape, internal structure, performance, interface, and modes of storing data.

These numerous changes have made HDDs stand the test of time. Not like other devices that became obsolete the moment they were introduced in the market. A floppy disk is a good example.

Hard Drive Types at a Glance

Currently, we can group hard drives into four types:

Parallel Advanced Technology Attachment (PATA)
Serial ATA (SATA)
Small Computer System Interface (SCSI)
Solid State Drives (SSD)
NVM Express

Parallel Advanced Technology Attachment

These were the first types of hard disk drives to be developed. They made use of the Parallel ATA interface standard to connect to computers.

These types of drives are the ones we refer to as Integrated Drive Electronics (IDE) and Enhanced Integrated Drive Electronics (EIDE) drives.

These PATA drives were introduced by Western Digital and Compaq back in 1986. They provided a common drive interface technology for connecting hard drives and other devices to computers.

Data transfer rate can go up to 133MB/s and a maximum of 2 devices can be connected to a drive channel. Most of the motherboards have a provision of two channels, thus a total of 4 EIDE devices can be connected internally. They make use of a 40 or 80 wire ribbon cable transferring multiple bits of data simultaneously in parallel. These drives store data by the use of magnetism.

The internal structure is made of mechanical moving parts. They have been superseded by serial ATA.

An EIDE Hard Disk Drive

Serial ATA Storage Drives

These hard drives have replaced the PATA drives in desktop and laptop computers. The main physical difference between the two is the interface.

SATA was announced in 2000 in order to provide several advantages over the earlier PATA interface. These are reduced cable size and cost (seven conductors instead of 40 or 80), native hot swapping, faster data transfer through higher signaling rates, and more efficient transfer through an (optional) I/O queuing protocol.

Their method of connecting to a computer is the same. Here are some advantages of SATA Hard Disk Drives. Worth noting is that their capacities vary a lot and so do the prices. When buying a disk drive, you need to know its storage capacity and how much storage you want.

SATA drives can transfer data faster than PATA types by using serial signaling technology.
SATA cables are thinner and more flexible than PATA cables.
They have a 7-pin data connection, with a cable limit of 1 meter.
Disks do not share bandwidth because there is only one disk drive allowed per SATA controller chip on the computer motherboard.
They consume less power. They only require 250 mV as opposed to 5V for PATA.

The interface of SATA Drive

A SATA Hard Disk Drive Pin Out
Wikimedia Commons

Small Computer System Interface (SCSI)

These are quite similar to IDE hard drives but they make use of the Small Computer System Interface to connect to the computer.

SCSI is a set of standards for physically connecting and transferring data between computers and peripheral devices. These standards define commands, protocols, electrical, optical, and logical interfaces.

SCSI drives can be connected internally or externally. Devices that are connected in a SCSI have to be terminated at the end. Here are some of their advantages.

They are faster.
They are very reliable.
Good for 24/7 operations.
Have better scalability and flexibility in arrays.
Well-adapted for storing and moving large amounts of data.

Solid State Drives

These are the latest in drive technology that we have in the computer industry. They are totally different from the other drives in that they do not consist of moving parts.

They also do not store data using magnetism. Instead, they make use of flash memory technology. They make use of integrated circuits or semiconductor devices to store data permanently, at least until it is erased. The basis for flash-based SSDs, flash memory, was invented by Fujio Masuoka at Toshiba in 1980 and commercialized by Toshiba in 1987.

The first commercial flash-based SSD was shipped by SanDisk in 1991. It was a 20 MB SSD in a PCMCIA configuration.

Advantages of Solid State Drives

Faster data access.
Less susceptible to shock.
Lower access times and latency.
Durability.
Less power usage.

A Solid State Drive (SSD)

NVMe Drive

Non-Volatile Memory Express (NVMe) is a storage interface introduced in 2013. “Non-Volatile” means data is not lost when the computer reboots or loses power.

The term “Express” refers to the fact that the data travels over the PCI Express (PCIe) interface on your computer’s motherboard.

This gives the attached disk drive a more direct connection with the motherboard. This is because data does not have to go through a Serial Advanced Technology Attachment (SATA) controller.

NVMe drives are thus much faster than SATA drives. PCIe 3.0 which is the current generation of the PCI Express standard has a maximum speed transfer of 985 megabytes per second (Mbps) on each lane. NVMe drives have been able to utilize 4 PCIe lanes, meaning a theoretical max speed of 3.9 Gbps (3,940 Mbps).

Meanwhile, one of the fastest SATA SSDs, the Samsung 860 Pro, tops out at reading and write speeds of about 560MBps.

NVMe drives come in several different form factors. The m.2 stick is the most common of these.

It is 22 mm wide and can be 30, 42, 60, 80, or 100mm long. These sticks are thin enough to lay flat on a motherboard. This makes them perfect for small form factor computers and laptops.

The PCIe-3.0 form factor is similar to a GPU and it plugs into any of the PCIe-3.0 slots on your motherboard. This is okay for full-sized ATX cases and motherboards.

However, it is constraining on small form factor PCs. On the other hand, it is impossible inside a laptop chassis.

NVM Express (NVMe)

Intel SSD 750 series, an SSD that uses NVM Express, in form of a PCI Express 3.0 ×4 expansion card (Front View)
Wikimedia