Solid State Drive vs. Hard Disk Drive: What's the Difference?

Solid-state drives have replaced hard disk drives as the storage of choice in nearly all new PCs, but some situations still require old-fashioned platter drives. Here's how to tell which one is best for your needs.

Solid state drives (SSDs) and hard disk drives (HDDs) are data storage devices. SSDs store data in flash memory, while HDDs store data in magnetic disks. SSDs are a newer technology that uses the physical and chemical properties of silicon to provide greater storage volume, speed, and efficiency. However, if you need to access data in blocks of 1 MB or more at a time, HDDs are a cost-effective option.

How Do SSDs Work?

Solid state drives (SSDs) contain nonvolatile flash memory, containing a variety of integrated circuits to store and retrieve data.

Inside an SSD, you'll find floating gate transistors in a grid pattern. Each row within these grids is called a page, with multiple pages making up a block.

The SSD stores information within these blocks. The individual charges on the floating gate transistors turn into binary ones and zeros. This binary is how the SSD transmits data. The SSD controller will track where specific data is stored within the drive, which allows you to access the data on your computer or laptop.

How do HDDs work?

Unlike solid-state drives (SSDs), Hard Disk Drives (HDDs) have multiple mechanical parts that move together to store and retrieve data.

Inside the HDD device, there are rotating platters with a magnetic coating. On each platter are tracks or concentric circles called segments. Each track and sector number creates a unique address that HDD technology uses to organize and locate data.

A motor rotates an internal actuator arm with a read/write head. By reading the charge information on particular segments, the read/write head records and retrieves information. An I/O controller and the HDD's operating system tell the mechanical parts what to do and when.

HDD vs. SSD: Key Differences

While both solid state drives (SSD) and hard disk drives (HDD) allow users to store files, they work differently. Many of the differences between SSDs and HDDs are due to the advancements made in technology.

The Reading Process

The reading process is how HDDs and SSDs retrieve data on their devices.

When you ask the HDD to retrieve data, a signal is sent to the I/O controller. The controller then signals the actuator arm, telling it where the required data is. By reading the charge of the bits at this address, the read/write head collects the data. The latency of an HDD measures how long it takes the actuator arm to move to the correct track and sector.

SSDs do not have moving parts. When you try to retrieve data, the SSD controller finds the address of that data block and begins reading its charge. If the block is inactive, a process called garbage collection begins. This process erases inactive blocks, freeing them for new data storage.

The Writing Process

The writing process is how HDDs and SSDs record new information.

Every track and sector in a Hard Disk Drive (HDD) is a new location to store data. When you try to save new data, the read/write head moves to the nearest available place. Once there, it changes the charge of any necessary bits, saving the information in binary to that track and sector. An internal HDD algorithm processes the data before writing it, which ensures that it is formatted correctly.

When you change or rewrite any part of the data on an SSD, it must update the entire flash block. First, the SSD copies the old data to the available blocks. Next, it erases the original blocks, rewriting the data with the changes to the new blocks. SSDs have extra internal space for moving and temporarily duplicating data. As a user, you cannot access this extra storage.

Performance

SSDs run faster than HDDs and use less energy. You can notice this when you move large files. SSDs can copy files at speeds of over 500 MBps. Newer SDDs can go up to 3,500 MBps. HDDs, on the other hand, only transfer at 30-150 MBps.

SSDs are also faster for running applications. They process read/writes at 50-250 MBps, while HDDs do so at 0.1-1.7 MBps. Hard Disk Drive speed is limited by the platter rotation speed. The platter rotation speed is limited to 4200–7200 revolutions per minute (RPM), making HDDs slower than electronic SSDs.

Storage Capacity

Both HDDs and SSDs provide adequate storage capacity. However, it is much more common to see larger HDDs because they are more cost-effective. Data storage on an SSD can cost $0.08–0.10 per GB, while HDDs cost only $0.03–0.06 per GB.

Durability

Hard Disk Drives(HDDs) have moving mechanical parts that make them vulnerable to breakage. If you drop an HDD, you can damage the actuator arms of the internal arms and thus damage the device. The moving parts of an HDD consume more energy and radiate heat, reducing the life of the device.

SSDs are more durable because they do not have any mechanical parts. They also consume less energy, which keeps them cooler. However, you can rewrite data on a block only a limited number of times.

To ensure that some blocks do not burn out before others, SSDs use a process called wear leveling. Wear leveling ensures that all blocks are used equally in read/write processes. SSDs also use a technique called trim, which helps skip the need to rewrite duplicate data when the SSD erases the original block.

Reliability

You can recover lost or corrupted data on both SSDs and HDDs. However, SSDs overwrite older data files, making recovery more complicated. You should go to an expert with the right equipment to recover data from a damaged SSD.

As a piece of technology, HDDs have been around for a long time. This, combined with their read/write processes, makes it easier to recover data from them.

That being said, none of these are impervious to data corruption. Therefore, data backup and recovery are best managed at the software level through redundancy and data deduplication.

When to use SSD vs HDD

When you need high speeds or have to deal with frequent reads/writes on large amounts of data, you should use a solid-state drive (SSD). SSDs are the better choice for data analytics or gaming workloads.

On the other hand, if you are dealing with data backup, data archiving, or throughput-intensive workloads, a hard disk drive (HDD) is the better choice. SSDs are more cost-effective for storing high volumes of data with less frequent access.