TradingKey - As solid-state drive prices fall and capacities increase, a long-held market view suggests that SSDs will eventually fully replace traditional mechanical hard drives. In the artificial intelligence era, this view appears even more convincing, as AI training and inference require high-speed reading of vast amounts of data, with SSDs clearly outperforming HDDs in latency, transfer speed, and random read/write performance.

However, AI data centers need to address not only how to read data faster, but also how to store massive amounts of data at a reasonable cost. From training datasets and model checkpoints to logs, backups, and AI-generated video content, the scale of data is expanding rapidly. In this environment, HDDs and SSDs are more likely to form a tiered collaboration rather than one medium completely replacing the other.

This also means that the investment thesis for Seagate Technology (STX) and Western Digital (WDC) has not disappeared with the adoption of SSDs, but is instead shifting from the traditional PC hard drive cycle toward high-capacity storage demand in AI data centers.

HDDs Will Not Disappear, But Use Cases Are Changing

SSDs use flash memory chips to store data and contain no mechanical parts, giving them advantages such as low latency, high IOPS, shock resistance, and low noise. Operating systems, databases, high-frequency trading, AI inference caches, and data requiring real-time access are better suited for SSDs. In personal computers and high-performance servers, the trend of SSDs replacing HDDs has become quite clear.

The advantage of HDDs, meanwhile, lies in cost per unit of capacity. For hyperscale cloud providers, as storage scale grows from PB to EB levels, subtle differences in cost per TB translate into massive capital expenditures. According to data released by Western Digital, the cost of enterprise-grade flash storage can still be 6 to 10 times that of HDDs, making it difficult for enterprises to store all data on SSDs.

AI has further reinforced this division of labor. GPUs and high-bandwidth memory handle computing, enterprise SSDs take on "hot data" requiring high-speed access, while HDDs store training materials, historical versions, logs, videos, backups, and data that does not require frequent access in the short term. Some data may remain in cold storage short-term, yet needs to be quickly restored when models are retrained—a demand that forms the primary market for high-capacity nearline hard drives.

Therefore, while SSDs will continue to erode consumer HDDs and certain performance-sensitive markets, completely replacing high-capacity HDDs in data centers remains uneconomical for the foreseeable future. The real shift in the HDD industry is that the revenue focus has moved from PCs and portable hard drives toward high-capacity cloud storage.

Why the AI Data Explosion Is Boosting HDD Value Again

Generative AI not only consumes data, but also continuously creates new data. Text, images, audio, video, and synthetic training data all need to be stored, and enterprises must also retain different versions of models, training logs, and compliance data. The larger the model scale and the longer the data retention period, the stronger the demand for low-cost capacity storage.

Meanwhile, Seagate and Western Digital are improving the economics of HDDs by boosting per-drive capacity. Higher-capacity hard drives can reduce server counts, rack space, network ports, and overall power consumption, allowing cloud service providers to store more data without proportionally expanding data center footprint.

Seagate is currently focusing on Heat-Assisted Magnetic Recording (HAMR) technology. Its Mozaic 4+ platform has completed qualification and entered mass production with two major cloud service providers, with per-drive capacities reaching up to 44TB. The company also plans to gradually increase per-platter capacity from over 4TB currently to 10TB, laying a technical foundation for future 100TB-class hard drives. Official data from Seagate shows that HAMR can increase capacity density while lowering the rack space and energy costs required per TB.

Western Digital is pursuing a dual-track strategy, extending the ePMR technology cycle while continuing to advance HAMR. The company's 40TB UltraSMR ePMR hard drive is currently undergoing qualification with two hyperscale customers, with plans to scale up production in the second half of 2026; HAMR products are expected to enter mass production in 2027 and progress toward the target of reaching 100TB capacity by 2029. Western Digital is also developing high-bandwidth and dual-actuator designs to address the long-standing performance limitations of HDDs. The technology roadmap released by Western Digital shows that the company aims to enter certain workloads previously handled mainly by QLC flash while maintaining HDDs' cost advantage.

These changes indicate that HDDs in the AI era are no longer merely traditional hardware products, but critical infrastructure for cloud service providers to control storage costs, rack density, and power consumption.

How Investment Logic Differs Between Seagate Technology and Western Digital

Judging from their latest financial performance, both companies are benefiting from a recovery in demand for cloud-based high-capacity hard drives, but their respective technology paths and risk profiles differ.

Seagate's fourth-quarter revenue for fiscal year 2026 reached $3.629 billion, up approximately 48% year-over-year; non-GAAP gross margin rose to 52.7%, and free cash flow reached $1.1 billion. Full-year revenue grew 34% to $12.195 billion, while full-year free cash flow hit a record $3.1 billion. The company expects first-quarter revenue for fiscal year 2027 to be approximately $4.1 billion and non-GAAP EPS to be around $7.30, reflecting continued strength in cloud customer demand and high-capacity product mix. Seagate's fiscal year 2026 results also showed that the company reduced $1.4 billion in debt over the full year and returned $810 million to shareholders through dividends and share repurchases.

Seagate's core advantage lies in its faster commercialization of HAMR. If its Mozaic platform continues to secure qualification from more cloud customers, the company is poised to maintain margins by leveraging capacity leadership, higher selling prices, and superior unit costs. However, HAMR requires the integration of precision lasers, magnetic heads, and manufacturing processes, leaving yield, reliability, and customer qualification risks during the production ramp. Although Seagate is reducing debt, it still had approximately $3.6 billion in total debt at the end of fiscal year 2026, and its balance sheet requires further improvement.

Following the spin-off of its flash business, Western Digital has become a purer HDD play. In February 2025, the original flash business was listed independently as SanDisk (SNDK), after which WDC's financial results primarily reflected the performance of its hard drive business. Filings submitted by Western Digital confirmed that SanDisk is no longer consolidated into WDC's financial statements following the completion of the spin-off.

In the fourth quarter of fiscal year 2026, Western Digital's revenue reached $3.747 billion, up 44% year-over-year; non-GAAP gross margin was 54.4%, and free cash flow reached $1.281 billion. Full-year revenue rose 36% to $12.919 billion, with full-year free cash flow totaling $3.511 billion. The company expects the midpoint of its first-quarter revenue for fiscal year 2027 to likewise be $4.1 billion, with a non-GAAP gross margin of approximately 55.5%. Western Digital's latest financial report shows that its most recent quarterly revenue, gross margin, and free cash flow were all slightly higher than Seagate's.

Western Digital's advantage lies in its ability to leverage mature ePMR and UltraSMR products to meet customers' near-term demand before gradually transitioning to HAMR, thereby reducing friction for customers forced into rapid technology platform shifts. However, a pure-play HDD model also deprives the company of the diversification provided by its former flash business. Should cloud customers cut procurement, HDD prices decline, or qualification progress slow, WDC's revenue and profits could experience more pronounced cyclical fluctuations.

Summary: Do Seagate and Western Digital Still Have Long-Term Investment Value?

HDDs will not be fully replaced by SSDs in the AI era, but their market positioning will continue to contract and focus on cloud data centers, enterprise storage, and high-capacity archiving. While consumer HDD demand may continue to decline, what truly determines the industry's outlook will be hyperscalers' exabyte-level procurement volumes, the pace of drive capacity upgrades, and storage costs per TB.

Both Seagate and Western Digital possess long-term investment value, but they are not low-volatility traditional value stocks; rather, they are storage targets that combine an AI growth narrative with hardware cycle risks.

Seagate is better suited for investors who prioritize its HAMR leadership, product capacity upgrades, and shareholder returns. The company has already achieved mass delivery of 44TB products and has a relatively clear technology roadmap; however, the market has high growth expectations for it, and its debt alongside HAMR mass-production execution still warrants ongoing observation.

Western Digital, on the other hand, provides purer exposure to high-capacity AI storage. Its latest gross margin and free cash flow performance are slightly superior, and its dual-track approach combining ePMR and HAMR offers greater flexibility. However, following the spin-off of its flash memory business, the company becomes more sensitive to HDD industry cycles and procurement schedules of major cloud customers.

Considering current operational quality, technological risks, and valuation margin of safety overall, Western Digital offers a relatively balanced risk-reward profile; for investors who prioritize HAMR tech leadership and the product premium brought by future 100TB hard drives, Seagate may exhibit greater growth elasticity. Regardless of the choice, investors should closely monitor cloud customer capital expenditures, exabyte shipments, cost per capacity unit, HAMR qualification progress, gross margins, and free cash flow, rather than simply equating AI data growth with sustained stock price appreciation.

The real industry trend is not SSDs eliminating HDDs, but rather a re-division of labor among different storage media based on speed, capacity, and cost. As long as global data growth continues to outpace the reduction in flash memory costs, high-capacity HDDs will remain an indispensable part of AI infrastructure.

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