Hard Disk Drive (HDD) Secondary memory

Primary memory has limited storage capacity and it is volatile. Secondary memory overcomes this limitation by providing permanent storage of data in bulk quantity. Secondary memory is also termed external memory and refers to the various storage media on which a computer can store data and programs. The Secondary storage media can be fixed or removable. Fixed Storage media is an internal storage medium like a hard disk that is fixed inside the computer.

What is a Hard Disk Drive?

The disk is divided into tracks. Each track is further divided into sectors. The point to be noted here is that the outer tracks are bigger than the inner tracks but they contain the same number of sectors and have equal storage capacity. This is because the storage density is high in sectors of the inner tracks whereas the bits are sparsely arranged in sectors of the outer tracks. Some space in every sector is used for formatting. So, the actual capacity of a sector is less than the given capacity. The read-write (R-W) head moves over the rotating hard disk. It is this Read-Write head that performs all the read and write operations on the disk and hence, the position of the R-W head is a major concern. To perform a read or write operation on a memory location, we need to place the R-W head over that position. Some important terms must be noted here: 

Hard Disk Drive

1. Seek time – The time taken by the R-W head to reach the desired track from its current position.
2. Rotational latency – Time is taken by the sector to come under the R-W head.
3. Data transfer time – Time is taken to transfer the required amount of data. It depends upon the rotational speed.
4. Controller time – The processing time taken by the controller.
5. Average Access time – seek time + Average Rotational latency + data transfer time + controller time.

Note: Average Rotational latency is mostly 1/2*(Rotational latency). 

In questions, if the seek time and controller time are not mentioned, take them to be zero. If the amount of data to be transferred is not given, assume that no data is being transferred. Otherwise, calculate the time taken to transfer the given amount of data. The average rotational latency is taken when the current position of the R-W head is not given. Because the R-W may be already present at the desired position or it might take a whole rotation to get the desired sector under the R-W head. But, if the current position of the R-W head is given then the rotational latency must be calculated. 

For Example –

Consider a hard disk with: 

• 4 surfaces 
• 64 tracks/surface 
• 128 sectors/track 
• 256 bytes/sector 

What is the capacity of the hard disk? 

• Disk capacity = surfaces * tracks/surface * sectors/track * bytes/sector 
  Disk capacity = 4 * 64 * 128 * 256 
  Disk capacity = 8 MB

The disk is rotating at 3600 RPM, what is the data transfer rate? 

• 60 sec -> 3600 rotations 
  1 sec -> 60 rotations 
  Data transfer rate = number of rotations per second * track capacity * number of surfaces (since 1 R-W head is used for each surface)
  Data transfer rate = 60 * 128 * 256 * 4 
  Data transfer rate = 7.5 MB/sec

The disk is rotating at 3600 RPM, what is the average access time? 

• Since seek time, controller time and the amount of data to be transferred is not given, we consider all three terms as 0. 
  Therefore, Average Access time = Average rotational delay 
  Rotational latency => 60 sec -> 3600 rotations 
  1 sec -> 60 rotations 
  Rotational latency = (1/60) sec = 16.67 msec. 
  Average Rotational latency = (16.67)/2 
  = 8.33 msec. 
  Average Access time = 8.33 msec.

Another example: GATE IT 2007 | Question 44

History of HDD

The hard disk was developed in 1953 by IBM developers who were looking for a solution to offer low-cost random access to large amounts of data. The first disk drives, which had a capacity of 3.75 MB and were the size of refrigerators, started to be shipped in 1956. Another early supplier of hard disk drive technology was Memorex, followed by Seagate Technology and Western Digital.

The size of hard disk drives has been getting smaller as technology has advanced. The 2.5-inch and 3.5-inch form factors were introduced and standardized in personal computers by the middle of the 1980s.

The storage capacity of latest hard disk drives is in the terabyte range, compared to the initial hard disk drives’ capacity of megabytes. HGST, formerly known as Hitachi Global Storage Technologies, is a Western Digital brand released the first 1 TB hard drives in 2007. In 2015, HGST introduced the first 10 TB hard drive. And in 2021, Western Digital introduced two 20 TB HDDs.

Why do Computers Need Hard Disks?

Hard discs are used to install operating systems, programmes, and other storage devices, they are also used to save documents. Computer users would be unable to save their files or documents on their computers because HDD maintain data after being turning off of the computer. This is why every computer need at least one storage device to permanently save data for as long as it is needed.

How do Hard Disk Drives Work?

Most basic hard drives are made up of numerous disk platters, which are circular disks composed of aluminum, glass, or ceramic that are arranged around a spindle inside a sealed chamber. The platter is spun by a motor attached to the spindle. The chamber also contains the read/write heads, which use a magnetic head to record information to and from tracks on the platters. The disks are additionally covered in a thin magnetic coating.

The platters rotate at up to 15,000 rotations per minute by the motor. A second motor regulates the location of the read and write heads that magnetically record and read information on each platter as the platters rotate. The compartments that store the data can be spread out all over the hard disk.

Hard Disk Drive Storage Capacity

• Three storage options 16 GB, 32 GB, and 64 GB. This is one of the lowest HDD storage space ranges and is often seen in older and smaller devices.
• There are two sizes 120 GB and 256 GB. This category is commonly regarded as an entry level for HDD devices like as laptops or desktops.
• 500 GB, 1 TB, and 2 TB are available. HDD storage of 500 GB or more is often deemed adequate for the average user. With this much capacity, users can most certainly save all of their music, photos, videos, and other information. Individuals with large-file games should find 1 TB to 2 TB of HDD capacity adequate.
• More than 2 TB of storage. Anything with more than 2 TB of HDD space is appropriate for users who work with high-resolution files.
• Recently, the highest capacity of HDD is 20 TB.

Hard Disk Drive Components and Form Factors

HDD have below components:

• Platters: Magnetic platters are disk-like in shape and used to store data. Typically, they are made from glass or aluminum and laid down on a spindle where layers of such disks are kept one after the other.
• Spindle: The spindle maintains the platters in place and rotates them as required. The Revolution Per Minute(RPM) rating controls how fast data can be written to and read from the hard drive.
• Actuator Arm: The actuator, also known as the head actuator, is a tiny motor that controls the movement of the read/write haed and monitors data transfer between the platters. It is in charge of ensuring that the read/write heads are always in the proper direction.
• Read/write Head: The read/write arm controls the movement of the read/write heads, that perform the actual reading and writing on the disc platters.

HDD have below form factors:

• 3.5 inches: Among the drive types that are common for desktops, 3.5-inch is the most commonly used form factor, it represent the approximate diameter of the platter within the drive enclosures
• 2.5 inches: These are used in laptop and other portable device and they also used to represent the approximate diameter of the platter within the drive enclosures
• 1.8 inches: The 1.8-inch drives are generally employed in extremely light and thin devices like tablets and some MP3 players with large storage capacity
• Enterprise Form Factor: Some HDDs are designed to be used in corporation environments and can are available larger form elements which includes 3.5-inch and a pair of.5-inch but with one-of-a-kind specs optimized for excessive-overall performance, reliability, and durability in server and garage structures.

Features of HDD

• Non-volatile: HDD is a non-volatile memory device, which means that the data stored on it persists even when the power is turned off. This makes it an ideal storage medium for long-term data storage.
• High Capacity: HDDs can store a large amount of data. Modern HDDs can store terabytes of data, making them an ideal choice for storing large files such as videos, photos, and audio recordings.
• Relatively Slow Speed: Compared to primary memory devices such as RAM, HDDs are relatively slow. The data access time for an HDD is typically measured in milliseconds, while the access time for RAM is measured in nanoseconds. This makes HDDs better suited for long-term storage rather than for frequently accessed data.
• Mechanical Parts: Unlike solid-state drives (SSDs), HDDs have mechanical parts that can wear out over time, leading to reduced performance or even failure. HDDs contain spinning disks and moving read/write heads, which can be susceptible to damage if the drive is bumped or dropped.
• Cost-effective: HDDs are generally less expensive than SSDs, making them a popular choice for budget-conscious users. This is particularly true for larger capacity drives.
• Reliable: While HDDs are not as reliable as SSDs due to their mechanical components, they are still considered to be a reliable storage medium. HDDs are designed to withstand heavy use and are often used in enterprise-level storage solutions.

Some Common HDD Errors

• Electrical Error: If a hard disc powers on but cannot read or write data , one or more of its components has most likely failed electrically.
• Logical Failure: Logical failure occurs when the hard disk’s software is hacked or stops working properly. All types of data corruption may leads to logical failure.
• Disk Failure: Disk failure occur when the hard disk is not working properly that may leads to data loss.
• Disk Full: One more common issue is Disk full Issue that occur when there is no more space on the disk to store data.
• Bad Sector: Bad sector failure occurs when the magnetic surface on a hard disk’s platter is displaced, making a specific area of the platter inaccessible.
• Firmware Failure: Firmware failure occurs when the software that performs maintenance duties on a disk becomes corrupted .

What are External HDDs?

External hard drives can be used as a portable data backup device or to increase a computer’s storage capacity. Through connectors like USB 2.0, USB-C, or External SATA (eSATA), external disks can be connected to a computer or other device. Additionally, compared to internal HDDs, external hard drives may transport data more slowly.

In addition to being able to increase a system storage capacity, an external hard drive also has the benefit of being portable. Users are able to physically carry their stored data on numerous devices with them wherever they go.

Advantages of HDD

• Capacity Limit: HDDs offer enormous stockpiling limits contrasted with other auxiliary memory choices, making them appropriate for putting away immense measures of information, including media records, reports, and applications.
• Practical: HDDs are by and large more savvy per unit of capacity contrasted with strong state drives (SSDs) and other fast stockpiling choices, pursuing them a favored decision for those requiring broad capacity without burning through every last cent.
• Mature Innovation: HDDs have been around for quite a while, making them a deep rooted and solid innovation. They’ve gone through various refinements and upgrades, coming about in vigorous, tried, and dependable capacity arrangements.
• Similarity: HDDs are viable with most PCs and working frameworks, guaranteeing simplicity of coordination and use across various stages.
• Successive Read/Compose Execution: In specific situations, especially with huge document moves or consecutive information access, HDDs can give fair read and compose speeds.
• Life span: With legitimate consideration and support, HDDs can have a moderately lengthy life expectancy, making them reasonable for long haul stockpiling needs.
• Data Maintenance: HDDs can hold information in any event, when controlled off, pursuing them a solid decision for putting away data for broadened periods.
• Information Recuperation: at times, information recuperation from a faltering HDD can be conceivable utilizing specific devices and strategies, giving an opportunity to recover important data even from harmed drives.
• Steady Overhauls: HDDs can be effectively updated or supplanted without broad specialized information. Clients can add more drives or supplant existing ones with bigger limits depending on the situation.
• Wide Accessibility: HDDs are broadly accessible in different structure elements, sizes, and capacity limits, making them effectively available for different registering needs.

Disadvantages of HDD

• For complex files HDD are slow.
• HDD produce huge amount of head while working.
• The mechanical part of Hard Disk Drive require more power to operate.
• HDD are less durable for especially for portable device.
• When HDD operates, it produces a lot of noise.

Frequently Asked Question on Hard Disk Drive – FAQs

Why does a computer need a hard drive?

We use Hard Drive to install operating systems, programs, additional storage devices, and to save data. If we don’t have hard disk in computer we are not able to save programs, files, or documents to their computers. HDD store data even after the computer is turn off.

What is a dynamic disk hard drive?

Dynamic disks hard drive manage data in a different way than traditional drives. Dynamic drives are more flexible and can store more data at a time, unlike traditional drives that might reserve a specific amount of space for the operating system.

What is stored on a hard drive?

A hard drive hold pictures, music, videos, text documents, and files. Hard drives also hold the files needed for the computer’s operating system and software applications.