The H.A.C.K.E.R. Project

Whether you are buying a prebuilt computer or plan to build one on your own, you have likely encountered the terms “HDD” and “SSD” when deciding on what type of storage you want for your device. Hard disk drives (HDDs) and solid-state drives (SSDs) are the two primary types of computer storage available for purchase. Both have various benefits and drawbacks, but the primary difference between the two is simple: “SSDs store data in flash memory, while HDDs store data in magnetic disks” (Amazon).

Hard Disk Drives (HDDs)

An HDD is “a type of data storage device that is used in laptops and desktop computers” and is the older of the two storage devices (IBM). While still in use today, HDDs “are more common in older devices” (Microsoft). During the early days of computing, HDDs were “massive, room-filling devices with a capacity of about 3.75 megabytes. Today, by comparison, an HDD that fits easily in a desktop computer can have upwards of 18 terabytes worth of storage” (IBM). HDDs are considered a non-volatile storage drive, “which means [they] can retain the stored data even when no power is supplied to the device”, making an HDD a great choice for long-term storage (IBM). In addition, there have been many other improvements made to the design of HDDs that allow them to remain a useful option for a computer today.

Physically, an HDD “contains a series of platters covered by a ferromagnetic coating. The direction of the magnetization represents the individual bits” (Villinger). The direct of the magnetization of a portion of a platter is modified using an electrical charge. The electrical charge “comes from the actuator arm or ‘read/write head.’ Read/write heads are instructed where to move on the platters by the software in the CPU and system board” (IBM). The platters themselves are “divided up into sectors. These sectors have thousands of subdivisions (called bits) that can all accept an electric charge. The bits of the sector and their corresponding charges are read by the read/write head and can be translated into binary as 1s or 0s” (IBM). Each platter has its own read/write head associated with it. Thus, in a basic sense, an HDD looks like multiple, extremely thin record players stacked on top of each other.

When in use, the operating system will “tell the HDD to read and write data as needed by programs. The speed that the drive reads and writes this data is solely dependent on the drive itself” (IBM).

When a CPU writes data onto the HDD, it uses a portion of a sector or sectors, depending on the size of the file. When an update occurs to the data, the CPU instructs the HDD to write it in the next available sector. The distance from the first sector to this new sector adds time to how quickly the data can be read. While the time is measured in milliseconds, more instances of data separation can cause a significant slowdown. This data separation is called “disk fragmentation,” and most OSs have a built-in program that defragments the disk, rearranging the data so that information for a program is in one place.

IBM

Unfortunately, since there are multiple moving components that make up an HDD, these devices tend to have some limitations. For example, “[a] precise [actuator] arm loses accuracy if the disk moves too quickly, and a disk can only spin so fast before it starts to warp or even break. Speeding up the platter to achieve the optimal rate takes time, and results in slower boot-up time” (IBM).

Solid-State Drives (SSDs)

The solid-state drive is the newer of the two memory storage devices which “implements integrated circuits rather than mechanical components for storage” (IBM). These integrated circuits are referred to as “flash memory” and consist of “individual memory cells storing bits that are instantly accessible by the controller” (Villinger).

Physically, “[i]nside an SSD, you will find floating gate transistors in grid patterns. Each row within these grids is called a page, with many pages forming a block” (Amazon).

Solid-state drives work by using electronic circuits to store and retrieve data. Data is stored in “blocks,” and these blocks can only be written fully once. To keep sequential data together and response times low, the block must be completely erased and rewritten on a different block. Unfortunately, the blocks are not durable and are damaged in the process of erasing. The writing/erasing is how wear occurs on an SSD and is why most SSDs come with integrated “wear-leveling” technology, which evenly distributes the wear out and extends the lifespan of the device.

IBM

SSDs “are often used in laptops because they’re non-mechanical. Solid state drives require less power, which translates into better battery life”; in addition, SSDs tend to be smaller and thinner than HDDs, which makes them even more useful for a laptop (Villinger).

HDD VS SSD

As previously mentioned, the primary “difference between a [solid-state] drive (SSD) and a hard disk drive (HDD) is how data is stored and accessed. HDDs use mechanical spinning disks and a moving read/write head to access data, while SSDs use memory chips” (Villinger). This difference, however, comes with varying benefits and drawbacks for HDDs and SSDs.

For one, “the speed at which an SSD accesses data is higher than an HDD speed” since SSDs do not utilize physical parts to handle data storage. (IBM). When an HDD accesses data, “a signal is sent to the I/O controller. The controller then signals to the actuator arm, telling it where the required data is. By reading the charges of the bits at this address, the read/write head gathers the data” (Amazon). When an SSD accesses data, however, “the SSD controller finds that data block’s address and begins to read its charge”, which not only takes less steps, but can drastically speed up data retrieval (Amazon). Furthermore, SSDs incorporate a process known as garbage collection to further maintain and organize data blocks. When accessing data, if the SSD finds that a “block is idle, a process called garbage collection begins. This process erases [the] inactive blocks, freeing them up for new data storage” (Amazon).

Not only that, but SSDs “use less energy than HDDs”, which, as stated previously, make them a great choice for portable devices or for those who wish to decrease the energy consumption of their computer (Amazon). This is directly a result of not having moving parts to handle data storage and access; in addition, the lack of moving parts makes an SSD a quieter option than an HDD.

While an SSD may seem like the better choice to some, it is important to consider that “HDDs are a better long-term storage device. SSDs tend to be less reliable for long-term storage because of data leaks that begin after a year of being unpowered” (IBM). SSDs store data with electricity; as with any electrical device, if it is not used, the device may begin to lose its charge. HDDs, however, store data with magnetism, which is less likely to degrade over time. What may be of even more interest to some, however, is that HDDs tend to be a lot less expensive to purchase than SSDs are.

Not only that, but the process of storing data itself may make an HDD a more attractive option, depending on your needs.

Every track and sector in an HDD is a new location to store data. When you attempt to save new data, the read/write head moves to the nearest available location. Once there, it changes the charge of any necessary bits, which saves the information in binary to that track and sector. An internal HDD algorithm processes data before writing it, which ensures it’s formatted correctly. 

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

Amazon

In a nutshell, an HDD is able to easily modify individual sectors and tracks for storage and does not need to update the entire platter when storing data. An SSD, however, has to update the entire block where data is being stored, regardless of whether the data is actually using the entire block or not. In theory, there is the extremely slim possibility for data loss, but what is affected more by this methodology is data recovery. While it is possible to “recover lost or corrupted data on both an SSD and an HDD”, it is much more difficult to recover lost data on an SSD (Amazon). This is due to how “SSDs overwrite old data files” making “recovery more complicated. You must go to a specialist with the right equipment to recover data from a damaged SSD” (Amazon).

Thus, whether you should aim for an HDD or SSD depends on your plans for your device. If you desire speed, efficiency, portability, and/or a quieter device, then an SSD may be the choice for you. If you desire long-term reliability, cheaper cost, and easier data recovery, then an HDD is the way to go. Alternatively, it is possible to build or purchase a device that has both an HDD and SSD, allowing you to get the benefits of both options.

Resources & Further Reading

Amazon AWS (Amazon). “SSD vs HDD – Difference between Data Storage Devices – AWS.” Amazon Web Services, Inc., Amazon, aws.amazon.com/compare/the-difference-between-ssd-hard-drive/.

IBM Cloud Education (IBM). “Hard disk drive (HDD) versus Solid-state drive (SSD): What’s the difference?” http://www.ibm.com, IBM, 16 Apr. 2024, www.ibm.com/think/topics/hard-disk-drive-vs-solid-state-drive.

Microsoft. “All about SSD, HDD, and Storage Types – Microsoft Support.” Support.microsoft.com, Microsoft, support.microsoft.com/en-us/windows/all-about-ssd-hdd-and-storage-types-9c6c7c59-7d1c-4611-9ba9-676d53cc0ff1.

Villinger, Sandro. “SSD vs. HDD: Which Do You Need?” SSD vs. HDD: Which Do You Need?, Avast, 30 June 2023, www.avast.com/c-ssd-vs-hdd.