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The difference between hard drives and SDD

When deciding what components to install or purchase for your computer, one of the big decisions you have to make is between an SSD and a hard drive. Both storage methods have their advantages, although most of the advantages of hard drives are based on the fact that the technology is more mature and has been the subject of extensive research and development for decades. This is in comparison to SSDs which have only become commercially available more recently and are still undergoing rapid technological improvements.

Tip: HDD means “Hard Disk Drive”, SSD means “Solid State Drive”.

What is the difference?

A hard drive is a rotating disk that uses magnetic storage to record information, modern hard drives have greater capacity by including multiple disks in a single disk enclosure and using both sides of each disk. To read or write data, a read/write head must pass directly over the part of the disk with which it interacts.

SSDs use flash memory to record electrical charge data on transistors. There are no rotating or moving parts in an SSD, data is written and read electrically. SSD research has developed a version of flash memory called V-NAND that physically stacks memory cells on top of each other, resulting in a significantly larger storage volume. Most modern SSDs consist of a TLC or QLC cell, with three and four levels, and each cell contains three or four bits of data, respectively.

Tip: V-NAND stands for Vertical NAND Flash. NAND flash is so called because the physical architecture of the transistors looks like a logical NAND gate. A NAND gate is a logic gate that performs a “not and” check, it is only false if all inputs are true.

Benefits of a hard drive

One of the main advantages of a hard drive is the price per storage unit, and hard drives cost about a tenth of the price of a similarly sized SSD.

Note: This applies primarily to high capacity drives, with little effect at lower capacities.

The largest hard drives commercially available in 2020 have 16TB of storage and cost around $470. In comparison, the largest SSD commercially available has a slightly smaller capacity at 15.36TB and costs almost ten times as much at US$4,295 . You have to reduce the capacity to just 2TB to get an SSD under $470.

With a capacity of 500GB, a low-end SSD would cost around US$60 with a high-end SSD twice as expensive. However, a hard drive costs between $20 and $30. As such, for any PC, hard drives are a much more cost-effective solution than using solid state drives.

Hard drives are less prone to the effects of aging if left in a safe environment. The load on an SSD’s memory cells decreases slowly, over a period of about two years for a used SSD, although this only affects SSDs disconnected from power sources. Flash memory in SSDs also suffers wear and tear and requires advanced wear leveling algorithms to extend the life of the drive. By comparison, hard drive drives do not suffer noticeable wear and tear, although the mechanical components used to read data can fail over time.

Advantages of SSDs

SSDs offer much faster read and write speeds than hard drives due to the inherent benefits of a lack of moving parts. SSDs are also designed to use faster connectors that hard drives can’t take advantage of, further increasing the performance disparity. The speed advantage means that any action that requires reading or writing data to the drive happens much faster with an SSD, this includes booting, loading videos, loading video games, virus scanning, etc.

Due to the lack of moving parts, SSDs are generally more resistant to physical shocks such as drops. However, some SSD form factors do not have a protective casing or coating and may be more vulnerable to breakage or damaged connector pins.

SSDs also do not experience any performance loss due to altitude, while HDDs can only operate safely up to 3000 meters / 10,000 feet. SSDs can operate at temperatures as low as -55 degrees Celsius. Long-term operation above 40 degrees Celsius is likely to shorten the life of an SSD, although thermal limiting measures prevent the worst effects. In comparison, hard drives can only operate between 0 and 55 degrees Celsius.

SSDs and hard drives have use cases. For typical home PCs, many people buy a mid-size SSD between 500GB and 1TB and then supplement it with a high-capacity hard drive. SSD is ideal for operating system and software that will benefit from high-speed storage, while high-capacity hard drive provides economical space to store necessary files and data.

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