Hard disk drives (HDDs) and solid state drives (SSDs) are the two main types of data storage devices used in computers. Both have continued to evolve in terms of storage capacity over the years, but SSDs have seen more rapid advancement recently. This article will examine the capacities of both HDDs and SSDs, looking at how they differ and how capacities have grown over time.
What is storage capacity?
Storage capacity refers to the maximum amount of data that can be stored on a drive, measured in gigabytes (GB) or terabytes (TB). The larger the capacity, the more data you can save on the drive.
For HDDs, capacity is determined by the number of disk platters inside the drive and the density of the data encoding on each platter surface. More platters and denser encoding allow for higher capacities.
For SSDs, capacity is determined by the number of NAND flash memory chips on the drive and the density of each chip. As with HDDs, more and denser chips enable larger capacities.
Typical capacities of HDDs
Consumer HDDs currently on the market typically range from 320GB on the low end to 10TB on the very high end. Some common capacities include:
– 500GB
– 1TB
– 2TB
– 4TB
– 6TB
Enterprise and server HDDs designed for businesses and data centers may go even higher, up to 16TB or more.
HDD capacities have increased rapidly over the years. In the early 2000s, 80-160GB was typical for desktop drives. The first 1TB consumer HDD was introduced in 2007. So in about 15 years, maximum capacities have increased by about 100x.
Typical capacities of SSDs
Consumer SSD capacities currently range from 120GB to 8TB, with 250GB to 2TB being the most common. Enterprise and data center SSDs may go up to 16TB. Some typical consumer capacities are:
– 120GB
– 250GB
– 500GB
– 1TB
– 2TB
As with HDDs, SSD capacities have also increased quickly. Early SSDs in the 1990s and 2000s were only a few gigabytes. The first consumer 1TB SSD arrived in 2009. So in roughly 20 years, capacities have grown by over 1000x.
Comparing HDD and SSD capacities
While both HDD and SSD capacities have increased greatly over the years, SSDs have advanced much more rapidly in the past decade. Today, the largest SSDs match or even surpass the capacities of the largest HDDs.
A few key differences:
– At the low end, HDDs still offer higher minimum capacities like 320GB versus 120GB for SSDs.
– In the mainstream consumer range of 500GB to 2TB, HDDs and SSDs now overlap extensively.
– For the highest capacities of 4TB+, HDDs still hold the advantage due to the mechanical nature of their storage being less costly per GB. The largest SSDs top out at 8TB but 16TB+ HDDs are available.
– Enterprise and data center drives for both HDDs and SSDs may offer up to 16TB or more. The overlap is greater at the cutting edge.
So in terms of maximum capacities, HDDs retain an advantage at the very high end due to fundamental density differences. But SSD capacities have essentially caught up with HDDs in the consumer space.
Factors impacting HDD capacity
Several factors influence the maximum capacities possible with HDD technology:
Platter Density
The primary factor is the areal density – how densely data can be stored on the magnetic platters inside the drive. This is measured in gigabits per square inch (Gb/in2). Current HDD technology can achieve densities up to about 1.1 Tb/in2. Higher densities allow for more data storage per platter.
Number of Platters
HDD capacities scale linearly with the number of platters inside the drive. More platters provide more total surface area to store data on. Modern HDDs typically have 2-8 platters.
Platter Size
Bigger platter diameters and thicker platters allow for more surface area per platter. Top-end HDDs utilize platters up to 3.5 inches in diameter versus 2.5 inches for smaller form factors.
Recording Technologies
New recording technologies like shingled magnetic recording (SMR) and two-dimensional magnetic recording (TDMR) can boost areal densities by partially overlapping data tracks on each platter.
Helium vs. Air
Filling HDD enclosures with helium instead of air allows for thinner platters and closer spacing, boosting density. However, helium drives currently carry a price premium.
By leveraging these kinds of advances, HDD manufacturers have consistently grown capacities over the decades. Further incremental areal density improvements will allow capacities to keep slowly increasing.
Factors impacting SSD capacity
For SSDs, key factors influencing capacity growth include:
NAND Lithography
The size of the lithographic process used to manufacture NAND flash memory cells impacts density. Smaller fabrication geometries allow packing more memory cell transistors onto a die. The lithography has shrunk from 800nm to 128 layers today.
Stacking Layers
3D NAND flash stacks memory cell layers vertically within the die for greater density vs. planar NAND with a single layer. SSDs now use up to 128 layers of 3D NAND. Increasing the number of layers boosts density.
Bits per Cell
Single-level cell (SLC) NAND stores 1 bit per cell, while multi-level (MLC) stores 2 bits, triple-level (TLC) stores 3 bits, and quad-level (QLC) stores 4 bits. More bits per cell increase density but reduce write endurance.
Die Capacity
Each NAND die has a fixed capacity based on the factors above. Current high-capacity dies are up to 1Tb. SSD capacities scale with the number of dies, up to 16 for a 16TB drive.
Thanks to rapid innovation in these areas, SSD makers have achieved massive density improvements and capacity growth over the years – much faster than HDD capacity gains.
Growth trends and projections
HDD capacity growth slowing
While HDD densities and capacities continue to grow, the rate of growth is slowing as limitations of current technologies like perpendicular magnetic recording are reached.
From 2020 to 2021, maximum HDD capacities increased only about 20% from 14TB to 16TB (Seagate). This contrasts with earlier periods where capacities often doubled year-over-year.
Looking forward, Seagate projects 2-3 more generations of capacity increases topping out around 40-50TB by the late 2020s using technologies like HAMR and MAMR. So capacities may 5x from today, but the rapid growth seen in the 2000s has slowed.
SSD capacity growth accelerating
SSD capacities are still on an exponential growth curve thanks to 3D NAND scaling. From 2019 to 2021, maximum capacities doubled from 8TB to 16TB as layer counts increased from 96 to 128 (Samsung).
Industry roadmaps point to SSD densities doubling every 2-3 years through at least 2030 via further 3D NAND stacking. 500 layers may be possible by 2030, enabling up to ~128TB consumer drives.
So while HDD growth is slowing, SSD capacities are projected to continue rapid, exponential increases for the foreseeable future before facing physical limitations.
Price per GB
While SSD capacities are now equaling or exceeding HDDs in many areas, HDDs continue to offer a lower price per gigabyte in higher capacities due to the mechanical nature of their storage.
Some example prices for specific capacity points:
| Capacity | 2.5″ HDD Price | 2.5″ SSD Price |
| 1TB | $35 | $80 |
| 2TB | $55 | $140 |
| 4TB | $85 | $400 |
While the SSD is much faster, the HDD is far less expensive per TB. For very high capacity bulk storage needs, HDDs remain considerably more affordable. However, at capacities of 1-2TB common for consumer systems, SSD pricing is now reasonably competitive.
Comparison summary
To summarize the capacity comparison between HDDs and SSDs:
– HDD capacities range from 320GB to 16TB for consumer drives, and up to ~50TB for enterprise.
– SSD capacities range from 128GB to 8TB for consumers, and up to ~16TB for enterprise.
– At the low end, HDDs offer smaller minimum capacities like 320GB versus 128GB for SSDs.
– In the mainstream 1-8TB consumer space, capacities extensively overlap now.
– For highest capacities, HDDs still have the edge up to ~50TB maximum vs. 16TB for SSDs.
– HDD capacity growth has slowed to ~20% per year recently as density limits are reached.
– SSD capacity growth remains on an exponential curve, doubling every 2-3 years with no slowdown in sight.
– SSD capacities are projected to surpass HDDs in all areas in the coming decade.
– HDDs maintain a significant price per TB advantage, making them ideal for high capacity bulk storage needs.
So in summary, SSD capacities are now equaling or exceeding HDD capacities in most consumer spaces thanks to rapid NAND flash innovation. But HDDs retain the edge for now in ultra-high capacities and price per gigabyte. Looking forward, continued exponential SSD density growth will likely surpass HDDs across all capacity segments in the next 10 years.
Conclusion
The capacities of HDDs and SSDs have increased enormously over the decades, enabled by steady advances in the underlying storage technologies. SSD capacity growth has been particularly explosive in the past decade thanks to 3D NAND flash memory. This has allowed SSDs to essentially catch up with and match HDD capacities in most consumer spaces from 120GB to 8TB. However, HDDs retain an advantage in the highest capacity tiers above 8TB and in price per gigabyte. Ongoing NAND flash improvements will likely allow SSDs to surpass HDD capacities across the board in the coming years, while HDD capacity growth is slowing. But HDDs will continue to serve an important role where cheap bulk storage is needed thanks to their fundamental mechanical design advantages.