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Difference between SSD and HDD: comparison

Both SSD - solid-state drive - and HDD - hard disk drive - are the most popular data storage options. Although cloud storage is on the rise, it still has a long distance to cover in order to give a run for money to these two. Both SSDs and HDDs are different in their physical specifications as well as the way in which each of them stores and processes data.

General Feb 17, 21 by Nisal N 9 min Read
Difference between SSD and HDD: comparison

Being significantly different from one another, both - solid-state drives and hard disk drives - have distinct advantages and disadvantages over one another. The decision about which of them to take mainly depends on the way you use your system and the purpose for which you require storage. Personal preferences might also play a role.

Anyways, before comparing the two, let us first understand how each of them works and what things come together to make them what they are.


Hard Disk Drives or HDDs have been around for 50+ years now. Over the course of their lifespan, these storage devices have cut the chunkiness and added to the maximum storage capacity at a gradual pace. HDDs have emerged as one of the most stable and mainstream forms of data storage.

The Operation

Hard disk drives store data in the form of magnetic fields. For reading and writing data, HDDs leverage spinning disks called platters. A typical HDD has:

  • An actuator arm with a read/write head for every platter.
  • One or many magnetically sensitive platters, and
  • A motor for spinning the platters and moving the actuator arm.

In addition to these hardware components, a hard disk drive also comes with an I/O controller. Some firmware serves as the software component for the HDD.

The I/O controller paired with the firmware makes communication between the HDD and the system - CPU - possible. This concludes how the hardware operates.

Each platter of the HDD corresponds to concentric circles dubbed tracks. Each track is divided into logical units known as sectors. A combination of a specific track and sector provides a unique address to store, locate, and organize data.

Usually, the hard disk drive writes data to the nearest available area. An algorithm is put in place that processes the data prior to writing it. This is done primarily to allow the firmware to detect and correct errors if it finds any.

The speed at which the platters spin is predetermined, and it varies depending on the HDD manufacturer and the device model. For HDDs corresponding to home desktops, it is anywhere between 4200 rpm to 7200 rpm. It directly corresponds to read/write rates i.e. the more the preset speed, the faster is the read/write rate.

As soon as a user gives the command to read data from an HDD, the I/O controller tells the whereabouts of the same to the actuator arm. The read/write head retrieves the data by reading the presence, or absence, of a charge in each of the provided addresses.

In case the user commands to update the data, then the read/write head changes the charge on the concerning track and sector.

Note - Latency defines the time required by the platter to spin and the actuator arm to locate the desired track and sector.


  • Tried-and-tested technology with 5+ decades of operations.
  • Costs less than SSDs for the same amount of storage.
  • Available in a range of shapes, sizes, form factors, and storage options.


There are certain limitations of hard disk drives that are mostly due to the reliance on mechanical parts - like actuator arm and read/write head - for reading and writing data. These are summed up as follows:

  • Mechanical parts are prone to damage if handled poorly. They might even miss read the data or fail in the worst cases.
  • Chunkiness is also a major concern. Although the latest HDDs are less bulky than their older counterparts, they are still bulky.
  • Requires more energy to operate as compared to SSDs.


Solid State Drives leverage a type of flash memory, NAND logic - the same that is used for USB drives, for fulfilling data storage needs as well as performing read, write, and update operations on the data.

Unlike HDDs that have a lot of mechanical parts, (like magnetic heads and spinning platters) SSDs are free from all of them. Thus, they are more durable and require less energy for their operation. To understand SSDs completely, we need to first understand the working of the NAND briefly.

The Operation

A NAND flash is made up of several floating gate transistors. At the basic level, floating gate transistors record the presence or absence of a charge for storing data. These gates follow a grid pattern that is further organized into a block, which can be of variable size. An SSD has multiple blocks. Each row forming the grid is dubbed a page.

An SSD controller is included for maintaining a track of the data and for managing a lot of other aspects, like executing firmware-level software. Whenever a retrieve or update data command is made, the SSD controller looks for the desired data at the related address and reads the charge status.

Updating data is a complex process in solid-state drives as the entire data in a block, where the change needs to be made, must be refreshed.

For doing so, the data on the concerned block is first copied to a different block. Thereafter, the target block is erased. Next, the entire data is rewritten to a new block with the required changes.

When an SSD is idle, garbage collection comes into play. This is a built-in process that ensures that the block whose information was updated is thoroughly erased. It ensures that the block is now available for writing data once again.

An important process of SSDs that one must be aware of is TRIM (known as UNMAP in the SCSI command set). It informs the SSD that it can skip rewriting some data while erasing data on a block. This is an important process as it prevents an SSD from premature wear as the number of times that a block can be rewritten is limited.

Another important process pertaining to SSDs is wear leveling. This algorithm ensures that each block of the SSD drive gets an equal number of read/write processes. It is an automatic process.

All SSDs come with an unreported additional data storage for facilitating data movement. This is called so because neither the operating system is aware of this extra storage nor it is accessible by the user. This simply aids data processing in a solid-state drive without affecting the overall storage capacity of the same.


  • Deliver faster loading speeds and data transfer speeds for applications, games, and movies.
  • Smaller in size compared to HDDs. Not bulky.
  • Low-energy consumption.


  • Newer technology.
  • Expensive option as compared to HDDs.
  • Large-capacity SDDs are rare.

Difference Between SSD and HDD (SSD vs. HDD)

So, now that we know the basics of the two contestants, it is time to compare them. A summary of the differences between SSD and HDD are explained as follows:

  • Cost - HDDs are, sometimes much, less expensive than SSDs. To give you an idea:
    • A Western Digital 240GB 2.5-inch SATA III Internal SSD costs around $34.5.
    • A 250GB Internal HDD from Western Digital costs only $25.8.
    • A 320GB SATA 3.5-inch HDD for desktop costs merely $13.5.
  • Durability and Reliability - While HDDs have mechanical parts in place, SSD does not. This is a crucial factor in determining the durability and reliability as mechanical parts, especially the ones moving and spinning, are prone to damages and failures.
  • Energy Usage - One of the main reasons for preferring SSDs over HDDs is power consumption. SSDs require much less energy than their counterpart.
  • Maximum Storage Capacity - One section that HDDs win over SSDs, for the time being, is maximum storage. While consumer SSDs (general) max out at a 2 TB, consumer HDDs (general) can be as big as 18 TB.
  • Speed - Solid-state drives easily outperforms hard disk drives in terms of data transfer speeds. Hard disk drives have data transfer speeds ranging between 0.1 to 1.7 MB/s. This is close to nothing when compared with 50 to 250 MB/s speeds delivered by SSDs.

SSD vs. HDD Comparison Table








Durability and Reliability



Energy Usage



Maximum Storage Capacity

8TB (typical)

2TB (typical)


0.1 to 1.7 MB/s

50 to 250 MB/s

First Appeared In

1957 (IBM 350 disk storage unit)

1978 (StorageTek STC 4305)

1987 (the first flash-based SSD commercialized by Toshiba)

The Verdict

Both hard disk drives and solid-state drives are the devices presently facilitating efficient data storage in modern computing systems. While HDDs are preferred as the built-in storage devices, SSDs are more preferred for drop-in (additional) storage options.

Choosing one between the two entirely depends on the requirements. If energy consumption and/or data transfer speed is the utmost factor, then SSD is the go-to option. For users prioritizing cost-effectiveness and higher storage capacity, HDD is the superior pick to make.

At 1Gbits we provide dedicated servers with both SSD and HDD storages.

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Nisal N

Computers has always fascinated me since I was a kid and here we are. I love travelling for 2 reasons: the first one to see a new part of the world and second (the most important one) to experience the rich culture hidden among the country and people. I'm pretty good at cooking but very poor when it comes to baking.

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