Hard drive sizes have increased dramatically over the past few decades. The first hard drive created by IBM in 1956 was just 5 MB. By the early 1980s, hard drives reached the 10 MB range. In the 1990s and 2000s, gigabyte and then terabyte sized drives became common.
Today, consumer hard drives typically range from 500 GB to 4 TB, with higher capacity drives reaching 10-16 TB. Data centers use drives up to 18 TB and prototypes up to 100 TB have been created.
However, there are physical and practical limitations on maximum hard drive size. Factors like physical platter size, mechanical precision, data encoding, and manufacturing feasibility restrict how large hard drives can become.
Physical Size Limitations
One key limiting factor for hard drives is the physical size and space available inside devices. Most consumer hard drives today use a 3.5 inch or 2.5 inch form factor.
3.5 inch hard disk drives, which are commonly used as internal desktop drives, have a width of 4 inches, a length of 5.75 inches, and a height of 1 inch. This sets a physical limit on the maximum platter size and thus drive capacity in this format. Manufacturers cannot simply make platters and drives larger without running into space constraints inside computer cases.
Smaller 2.5 inch hard drives designed for laptops have even tighter space requirements, with a maximum width and length around 2.75 inches. While advances in areal density continue to boost capacities, these form factors place a cap on the potential physical size of the platters and overall drive volume.
According to List of disk drive form factors – Wikipedia, many early hard disks were limited to heights of 1.625 inches or less to fit in spaces originally meant for floppy drives. So space constraints have always factored into drive sizes.
Data Density Limits
One key limit to hard drive capacity is data density, which refers to how many bits can be stored in a given physical area on the disk. This is commonly measured in bits per square inch (bpsi). In 2017, leading hard drive manufacturers achieved a density of around 1 terabit (1 trillion bits) per square inch (Western Digital). However, in recent years, the rate of density improvements has slowed. From 2016 to 2021, density only increased from ~900 Gbpsi to 1 Tbpsi, even as drive capacities grew from 10TB to 20TB (Tom’s Hardware).
To continue increasing density, companies are investing in new technologies like shingled magnetic recording (SMR), two-dimensional magnetic recording (TDMR), and heat-assisted magnetic recording (HAMR) which use overlapping tracks, advanced heads, and laser heating to pack more data into the same space (Forbes). However, the rate of density growth has still slowed dramatically compared to previous decades. Overcoming these physical limitations to continue growing HDD capacity will require major technical innovations.
Addressing Limits
Older hard drives used a system called CHS (cylinder-head-sector) addressing to identify the location of data. This limited the maximum addressable capacity to around 8 TB due to a maximum of 255 heads, 63 sectors per track, and 1024 cylinders per platter [1]. To overcome this limitation, a translation scheme called logical block addressing (LBA) was introduced, which simply sequentially numbered all the sectors on a drive [2].
However, even LBA has its limits. Standard LBA addresses use 32 bits, limiting the maximum individual block address to 2^32, or 4,294,967,296 blocks. With a block size of 512 bytes, this allows for a maximum drive capacity of 2 TiB. To support larger drives, 48-bit LBA was introduced, pushing the limits to 128 PiB. Currently, some drives are pushing past the 48-bit limit, so standards bodies have introduced even larger address spaces like 512e and 4Kn formatting to support massive drives up to 16 EiB [2].
Theoretical Limits
There are theoretical limits that constrain how much data can be stored on a hard drive based on fundamental principles of physics and information theory. The most well-known is the Shannon limit, formulated by Claude Shannon in his 1948 paper “A Mathematical Theory of Communication.” This establishes an upper bound on the maximum data rate or channel capacity through a channel with a given bandwidth and signal-to-noise ratio. For any communications system, as the noise increases, the maximum error-free data rate decreases. The Shannon limit defines the theoretical maximum rate at which information can be transmitted over a communications channel, which translates to a limit on data density on storage media like hard drives.
In addition, there are thermodynamic limits arising from the physical nature of the magnetic grains that store data on a hard drive platter. As grains get smaller to pack in more data, thermal fluctuations can spontaneously flip their magnetic orientations, leading to read/write errors. This superparamagnetic limit constrains how small and tightly packed the grains can be, putting a cap on maximum data density.
Current Largest Drives
Hard drives have continued to increase in size and capacity over the years. As of 2022, some of the largest hard drives include:
- The Seagate Exos X20, announced in March 2022, offers record capacity at 20TB for a 3.5-inch hard disk drive (HDD). It uses shingled magnetic recording (SMR) technology to achieve the increased density. (Source)
- Western Digital announced a 20TB SMR HDD, the Ultrastar DC HC570, in August 2021. It leverages their OptiNAND technology to provide the expanded capacity. (Source)
- Toshiba unveiled 26TB MG09 HDDs in February 2022 using conventional magnetic recording and their flux control microwave-assisted magnetic recording (FC-MAMR). This set a new record for convential HDD capacity. (Source)
Hard drive manufacturers continue to push the limits on HDD capacity through advanced technologies like SMR and MAMR. While SSDs have far surpassed HDDs in performance, HDDs remain highly relevant for affordable mass storage. The largest HDD capacities are ideal for data archives, cloud storage, and other high capacity applications.
Alternative Storage
SSD capacities continue to increase, with consumer models going up to 8TB as of 2022. However, SSDs do have limitations due to how data is stored on NAND flash memory cells. Each cell can only store a certain number of bits, so increasing density requires more advanced manufacturing processes.
Hybrid drives combine an SSD and traditional hard disk drive to balance speed and capacity. The SSD acts as a cache for frequently accessed data, while the HDD provides more storage. Hybrid drives can deliver some of the benefits of an SSD without the high cost per gigabyte.
Cloud storage offers essentially unlimited capacity by storing data on remote servers accessed over the internet. Services like Dropbox, Google Drive, Microsoft OneDrive and iCloud provide abundant storage and access from multiple devices. However, internet connectivity is required and there are monthly fees based on usage levels.
Practical Limits
While hard drive sizes continue to increase, there are diminishing returns on very large drives for most home consumers. According to a 2023 Reddit thread, drives above 16TB offer more storage than the average user needs, and the cost per TB becomes less economical (1). For a home desktop or laptop, most users find drives in the 1-8TB range sufficient, with higher capacities reserved for specialized uses like servers or data archives (2).
Ultra-high capacity drives above 50TB start to exceed practical limits for general computing. As stated in a 2021 AnandTech article, once drives pass about 50TB, even filling the drive becomes difficult, and use cases are limited outside of highly specialized applications (3). While drive sizes will continue growing, for most home and business uses, capacities in the 10-20TB range deliver the best balance of space, affordability and practicality.
In the end, ideal drive size depends on individual use cases and storage needs. For most desktop PC and laptop users, drives in the 1-10TB range offer ample capacity without the added costs and complexity of managing an extremely large drive.
Sources:
(1) https://www.reddit.com/r/DataHoarder/comments/zaii41/what_hdd_size_would_you_recommend_for_202223/
(2) https://www.techradar.com/news/10-best-internal-desktop-and-laptop-hard-disk-drives-2016
(3) https://www.anandtech.com/show/16544/seagates-roadmap-120-tb-hdds
The Future
Many experts predict that hard drive sizes will continue to grow in the coming years. According to a technology roadmap from the Advanced Storage Technology Consortium, hard drive capacity could reach 100TB by 2025, enabled by new technologies like heat-assisted magnetic recording and microwave-assisted magnetic recording.
However, some believe the days of dominant hard drive growth may be numbered. As solid state drives continue dropping in price and growing in capacity, they may begin replacing hard drives, especially in consumer devices and laptops. However, HDDs still maintain significant advantages in price per terabyte in high capacities, so they are likely to continue dominating the data center and NAS storage markets in the foreseeable future.
Other emerging storage technologies like DNA data storage and atomic-scale storage could one day allow data densities far beyond what current magnetic drives can achieve. However, most experts think these technologies are still many years away from wide commercial viability. Barring a major new discovery, hard drives will likely remain the dominant high-capacity, low-cost storage technology through at least the end of this decade.
Overall, while hard drive capacities may be approaching theoretical limits over the next 5-10 years, incremental improvements in recording density should allow capacities to keep slowly growing in the near future. However, the long-term trajectory will depend both on the pace of recording density improvements and the degree to which solid state drives continue displacing HDDs in some applications.
Conclusion
In summary, there are both physical and theoretical limits to how large hard drives can become. Physically, drives are limited by the space available inside a computer case and the maximum number of platters and heads that can fit. Theoretically, drives are limited by the maximum addressable capacity possible with current interfaces. However, new technologies enable continued increases in data density.
Currently, the largest hard drives available to consumers are around 20TB. Enterprise drives can reach much higher capacities. In the future, capacities may expand into the range of 100TB or more as data density improves through technologies like HAMR, MAMR, and SMR. However, there are diminishing returns in making ever-larger drives for typical consumer use cases.
For most home and business users, drives in the 10-20TB range are more than sufficient. Though some power users may desire larger drives, typical needs can be met by combining multiple, reasonably-sized drives in RAID setups. Overall, while there remains room for growth, current hard drive technology already provides abundant storage for the majority of users.