What is an HDD (Hard Disk Drive)?

HDD (Hard Disk) is a storage device that uses a series of rotating magnetically coated disks called platters to store data or programs.

What is a Hard Disk?

Hard Disk, in daily usage, means hard disk or hard drive because the disk and drive mechanisms are the same.

A typical hard disk platter drive spins up to 3600 rpm. The read/write heads float on a buffer of air 10 to 25 million inches thick. Therefore, it should not come into contact with the recording surface.

It prevents airborne dirt from entering. That’s why the entire disk drive is hermetically sealed.

Hard Disk capacity can offer storage space from megabytes to terabytes. Additionally, as disk size increases, backup strategy becomes more critical.

Hard disks are reliable, but they can fail at the most inopportune moments. It preserves information even in case of energy loss by using a Digital Magnetic Recording system. Therefore, hard drives are safe.

There are different standards for connecting a hard drive to a computer. The most common interfaces are ATA/IDE, SCSI, SATA, and FC. ATA/IDE is primarily used in servers. SATA was standardized in 2004. It is remarkable for FC servers.

When it leaves the factory, the hard disk does not contain an operating system. A low-level format must be set before defining partitions. So it can be understood by the system.

Solid State Disks are a type of memory that stores information with semiconductors. This type of disk was initially limited to supercomputers. However, it is now also available on personal computers. Despite their high prices, cheaper, low-capacity drives are available.

As a result, the Track Cache solid-state hard drive has RAM-type memory inside.

Hard Disk (HDD) History

Initially, hard drives were removable. However, nowadays, it is found in fixed boxes.

In 1956, the first hard drive was introduced. Introduced with the Ramac I was the IBM 350 Model 1. This drive weighed a ton and had a capacity of 5 MB.

This hard drive was more significant than a refrigerator. Additionally, it operated with vacuum valves and required a separate console.

Its most significant advantage was that the access time was constant. Access times were different for magnetic tapes. The reels had to be wound to find the desired data.

Hard disk technology started simple. A metal disc was coated with magnetic material. It was then divided into sectors.

The magnetic head encoded the information. Binary code was used as zeros and ones. This way, the recorded bits could remain intact.

Initially, the bits were arranged horizontally. However, more compact recording methods have been discovered.

Frenchman Albert Fert and German Peter Grünberg discovered giant magnetoresistance. This created more sensitive read and write heads. It also enabled tighter registration of bits.

These discoveries led to growth in storage capacity. In the 1990s, capacity increased by 60% annually.

In 1992, 3.5-inch hard drives had a capacity of 250 MB. Ten years later, it exceeded 40 GB. Today, disks with terabyte capacities are available.

Additionally, the first Hard Disk mobile phones were introduced in 2005. Samsung and Nokia offered these phones.

HDD Components

The components inside a HDD are:

• Disc platters on which data is recorded.
• Read and write head.
• The motor that rotates the disk platters.
• Electromagnet component that moves the head.
• Cache.
• Electronic control circuit.
• Moisture protective bag.
• Outer box component to protect from dirt and dust.
• Vent hole.
• The screw-type component is also Torx.

HDD Features

Features to consider when purchasing a Hard Disk are:

1) Average Access Time

The average time it takes for the head to reach the desired sector on the disk surface is the sum of Average Seek Time, Read/Write Time, and Average Latency.

2) Average Call Duration

The average time it takes for the head to reach the desired track is half the time it takes to travel from the most peripheral to the most central path of the disk.

3) Read/Write Time

The average time it takes for the disk to read or write new information. It depends on the amount of information you want to read or write, block size, number of rounds, time per round, and number of sectors per chunk.

4) Average Latency

The average time it takes for the head to be in the desired sector is half the time it takes to spin an entire disk.

5) Rotation Speed

They are the revolutions per minute of the disk platters. The higher the slew rate, the lower the average latency.

6) Transfer Rate

It is the speed of transferring information to the computer after the head is positioned on the right track and sector.

7) Cache

It is a RAM inside the hard drive. Solid-state hard drives use certain types of memory built with semiconductors to store information.

8) Socket Type

It is an interface communication medium between the hard drive and the computer, such as IDE/ATA, SCSI, SATA, USB, Firewire, and SAS.

Currently, new-generation disks use Perpendicular Recording (PMR) technology, which provides higher storage density.

There are also disks called GP (Green Power) that use energy more efficiently.

SSD disks, one of the new HDD types, are high-speed because they have no moving parts and consume less energy.

Hard Disk Physics Structure

A hard disk has one or more platters spinning simultaneously. The reading and writing device is a set of arms. These arms are aligned vertically and move simultaneously.

There are read/write heads at the ends of the arms. These heads read both the inner and outer areas of the disk. Each tray has two faces. Therefore, one read/write head is required for each face.

Each of the arms is double. Each reads the top and bottom faces of the plate. Therefore, eight heads are required to read four plates. However, not all faces are always used for commercial reasons. That’s why hard drives sometimes have an odd number of heads.

Read/write heads never touch the disk. As it rotates, a thin layer of air forms between the plates. This layer is three-millionths of a millimeter wide. If a head touches the surface of the plate, it will cause severe scratches. This depends on how fast the plates are spinning.

Addressing

There are platter, face, head, track, cylinder, and sector concepts that the disk uses as addressing:

• Plate: Each of the disks in the drive.
• Face: It is the two sides of a plate, upper and lower.
• Head: It is the end device that performs writing and reading operations.
• Track: A perimeter within a face.
• Cylinder: These are vertically aligned circles consisting of several parts.
• Sector: Each section of a track. The sector size is not fixed; the current standard is 512 bytes.

In the past, the number of sectors per track was fixed, which was significantly wasted because more sectors could be stored from external tracks than from the inside.

Thus, ZBR technology emerged, which increases the number of sectors on external tracks and uses the hard disk device more efficiently.

The first addressing system used was CHS. Because with these three values, any data on the disk could be placed.

Later, a more straightforward system called LBA was created, which consists of dividing the entire disk into sectors and assigning a unique number to each.

Hard Disk Connection Types

The hard disk contains different types of connections to the motherboard, be it SATA, IDE, SCSI, or SAS.

1) IDE Connection Type

IDE or ATA is the leading standard for the versatility and quality of mass storage devices such as hard drives and ATAPI (Advanced Technology Attachment Packet Interface).

2) SATA Connection Type

It is the new connection standard that uses a serial bus for data transmission.

It is noticeably faster and more efficient than the IDE and comes in three versions;

• SATA1: Transfer speed is 1.5GB.
• SATA2 Transfer speed is 3GB.
• SATA3: Transfer speed is 6GB.

3) SCSI Connection Type

They are hard drives with large storage capacity.

The average access time can reach seven milliseconds. The sequential information transmission rate can theoretically get 5 Mbps on Standard SCSI disks, 10 Mbps on Fast SCSI disks, and 20 Mbps on Wide-speed ​​SCSI disks (SCSI-2).

The SCSI controller can handle up to 7 daisy-chained SCSI hard drives. Unlike IDE disks, they can operate asynchronously relative to the microprocessor, making them faster.

4) SAS Connection Type

The successor to parallel SCSI is the serial data transfer interface. However, SAS continues to use SCSI commands to interact with data devices.

It increases speed and allows quick connection and disconnection.

One of the main features is that it increases the transfer rate by increasing the number of connected devices, i.e., ending the limitation of 16 devices available in SCSI, as well as being able to manage a fixed transfer rate for each connected device.

In addition, the connector is the same as in the SATA interface, allowing the use of these hard drives for applications with less need for speed, saving costs.

Therefore, SAS controllers can use SATA disks, but not vice versa, because the SATA controller does not recognize SAS disks.

HDD Dimensions

The oldest form factor of complex disk devices inherited their size from floppy disk drives.

They can be mounted in the same chassis. For this reason, form factor hard disks were colloquially called FDD types floppy disk drives.

Form factor compatibility remains 8.89 cm (3½ inches) even after other smaller-sized floppy disk types are removed.

8 inch HDD

In 1979, Shugart Associates released the SA1000, the first form factor with the exact dimensions and compatible with the 8-inch interface of floppy disk drives.

5.25 inch HDD

This form factor is the same size as Seagate hard drives introduced in 1980. It also uses a maximum length of 82.5 mm, with a maximum FDD height of 5¼ inches.

Most 120 mm optical drive (DVD/CD) models use the 5¼ half-height form factor size, which is also used for hard drives.

The Quantum Bigfoot model was the last model used in the late 1990s.

3.5 inch HDD

This form factor was first used by Rodine hard drives, which are the same size as 3½, 41.4 mm tall drives.

2.5 inch HDD

This form factor was introduced by PrairieTek in 1988 and is entirely different from the size of floppy disk drives.

This is often used by mobile computer hard drives and replaced 3.5-inch drives in 2008.

Today, this disk size is more common in laptop drives.

1.8 inch HDD

This build factor was introduced by Integral Peripherals in 1993 and dealt with ATA-7 LIF in the specified sizes. Its use in digital audio players increased significantly.

The original variant has 2GB to 5GB and fits into a PC expansion card slot. They are usually used in iPods and MP3-based hard drives.

1 inch HDD

This form factor was introduced by IBM and Microdrive in 1999 as suitable for compact flash type 2 slots. Also, Samsung uses the same factor as 1.3 inches.

0.85 inch HDD

Toshiba announced this form factor on January 8, 2004, for use in mobile devices and similar apps. This includes SD/MMC slots that are compatible with HDDs optimized for video and 4G micro mobile storage.

Naming disc sizes in inches does not usually describe existing products. Still, it does indicate the relative size of the disc for the sake of historical continuity.

Durability and Fault Tolerance

Narrow space between HDD heads and surfaces leads to data loss. If the read/write heads scratch the disk, data will be lost.

These accidents can be the result of electronic failure, power outage, physical shock, or wear and tear. Poorly manufactured heads can also cause this condition.

The axis of the Hard Disk depends on the air pressure and correct heights within the enclosure. The hard drive requires a specific air pressure to function correctly.

Outdoor connection and pressure occur through a small hole with a filter. If the air pressure is too low, there will not be enough space between the head and the disc. This may cause data loss.

Therefore, disks that can operate at an altitude of approximately 3 kilometers are required. The pressure altitude in modern aircraft is 2.6 KM. Consequently, it has a pressurized cabin. Therefore, you can safely use your everyday Hard Disk devices during flights.

Modern disks contain temperature sensors and adjust according to environmental conditions. Ventilation holes are located on all discs. They have a sticker on the side that warns the user not to cover the hole.

The air inside the disc is in constant motion. This air removes contaminants by passing through the internal recirculation filter.

High humidity for long periods can corrode the heads and plates. Large magnetism-resistant heads may overheat due to friction and contamination. Moreover, data can be read for a short period.

The electronic components of the HDD control the direction of the actuator and the rotation of the disk. Additionally, it performs read and write operations.

Firmware efficiently programs reads and writes to the disk surface. As a result, it may reassign failed sectors.

Producers

The development of modern disks is the monopoly of large companies. Since 2007, Seagate, Western Digital, Samsung, and Hitachi have produced 98% of the world’s hard drives.

Fujitsu continues to produce portable and server disks. However, it stopped producing desktop discs in 2001 and sold them to Western Digital.

Toshiba is a leading manufacturer of 2.5 and 1.8-inch laptop drives. ExcelStor is a small hard drive manufacturer.

The first victim in the PC market is Computer Memories Inc (CMI). In 1985, faulty 20 MB disks destroyed his reputation. CMI withdrew from the hard disk market in 1987.

Another central area for improvement is MiniScribe. It went bankrupt in 1990 due to fraud. Micropolis survived until 1997. JTS disappeared a few years later, in 1999. He tried making hard disks in India.

Rodime was a significant producer in the 1980s. It stopped producing discs due to restructuring in the 1990s. It focused on licensing technology. It also holds patents related to the 3.5-inch format.

Signs of Damage

If you do not have software that detects failures of an HDD, some symptoms indicate that the disk is about to fail.

• Irregular crashes or freezes, especially when the operating system is started.
• Interrupting or altogether canceling the process while copying a file.
• Self-changing file or folder names.
• Pointless deletion of files.
• When you want to open a folder or file, the process takes too long.
• Sizzling noises coming from the Hard Disk.

The sounds coming from the HDD are essential. This indicates the possibility of your disk becoming corrupted. It also shows a state of deterioration in a short time. However, SSD disks do not have this symptom because SSD disks are not mechanical.

Modern hard drives use SMART technology. SMART helps detect and indicate faults. Additionally, various applications read SMART data.

Suppose your disk’s SMART feature reports a problem; back up your data immediately. It is recommended that an external disk be used for backup.

Also, a Bad Sector can occur on an HDD. This prevents saving and reading data. Moreover, it can render your device completely unusable.

So, you should check the health of your disk and make sure it is in good condition.

Performance Measurement

Performance speeds may vary depending on the brand and model of your Hard Disk device. Mainly, if you use a new type of disk, such as SSD, data reading and writing speeds will be faster. You can even revive your old computer with an SSD.

You can use various software to test the reading and writing performance of your HDD. The most used software in this process is CrystalDiskMark.