"Memory stocks" covers several different businesses. High-bandwidth memory (HBM) is a custom product sold to a handful of AI chip companies on long contracts. Commodity DRAM and NAND flash are sold on contracts that reset quarterly. Hard drives are made by three companies with years of supply discipline behind them. All three rallied together in 2026. They do not face the same risk when supply catches up, and one of them got a reminder in October.
If you only read one thing
The short version: Micron has already agreed most of its 2027 HBM supply at higher prices, so HBM revenue is the most locked-in part of the memory trade. Hard drives looked locked in too, because nobody was building factories, until Toshiba said on October 2 it would double its capacity. Seagate and Western Digital fell about 11% that day. The market had priced the hard-drive makers at 15 to 16 times forward earnings, more than double the flash and DRAM makers, so they had the most to lose from new supply.
HBM: contracted, custom, concentrated
HBM is DRAM stacked in layers and packaged beside an AI chip. Only SK hynix, Samsung, and Micron make it in volume, and each customer qualifies each supplier's product separately. That makes it the opposite of a commodity.
It is also sold further ahead. In its September results, Micron said it had agreed sales for the vast majority of its calendar 2027 HBM supply, at significant price increases, according to its prepared remarks. SK hynix, the HBM leader, is reported to supply about two-thirds of Nvidia's HBM4 for its Vera Rubin platform.
Contracts cut both ways. TrendForce notes that some suppliers' server DRAM price increases lag the market average because of terms in long-term agreements. Locked-in volume also means locked-in prices.
The takeaway: HBM is sold on long contracts to a few customers, and Micron has already agreed most of 2027. That makes HBM revenue the most visible part of the memory trade, at the cost of some upside when spot prices run.
Hard drives: discipline, until October 2
Hard drives still store most of the data in cloud data centers because they cost far less per terabyte than flash. Seagate and Western Digital make most of them, with Toshiba a distant third. Through 2026, both leaders grew revenue mainly by raising prices and shipping higher-capacity drives rather than more units. Seagate's revenue rose 47% in its June quarter while capacity shipped rose 34%, and its CFO said in March that its factories were full with no interest in adding units.
That discipline was the bull case. On October 2, Toshiba said it would double its hard-drive capacity and aim for 30% market share. Seagate fell 11.6% and Western Digital 10.9% that day, according to ZeroHedge's report on the Toshiba plan.
The takeaway: The hard-drive rally rested on three makers not adding capacity. Toshiba's plan to double its own is the first crack, and the stocks reacted the same day.
Flash: the most new supply on the way
NAND flash sits between the two. Prices are rising fast, with TrendForce expecting another 15% to 20% in the fourth quarter, and SanDisk grew revenue 51% in a single quarter, two-thirds of it from price. But flash also has the most announced capacity. YMTC's third Wuhan plant, split between DRAM and NAND, targets production in 2027. SK hynix approved a new NAND fab, M17, in Cheongju. Micron is building a NAND facility in Singapore due to begin output in the second half of 2028.
The takeaway: Flash prices are rising fastest, but flash also has the most new capacity announced, from China, Korea, and Singapore.
How the market prices each layer
| Ticker | Layer | EV/Sales 5y %ile | Forward P/E | Revenue growth |
|---|---|---|---|---|
| MU | DRAM and HBM | 96.2* | 5.7x | 167% |
| 000660.KS | DRAM and HBM | snapshot only | 3.9x | 257% |
| SNDK | Flash | 52.0† | 6.8x | 175% |
| STX | Hard drives | 92.5 | 14.7x | 34% |
| WDC | Hard drives | 83.5 | 16.1x | 36% |
Before Toshiba's announcement, the market treated hard drives as the most durable part of the trade. At 15 to 16 times forward earnings, Seagate and Western Digital were valued at more than twice the multiple of Micron or SanDisk, whose earnings investors heavily discount. The HBM leaders, with the most contracted revenue, trade at the lowest forward multiples of all, partly because most of their sales are still commodity DRAM and NAND.
That ordering is worth watching. If the market starts to treat HBM as contracted revenue and hard drives as a commodity again, the forward multiples could swap places. Compare Seagate's EV/Sales history with SanDisk's to see how differently the two have moved.
The takeaway: The market priced hard drives as the safest layer and the DRAM makers as the most cyclical, even though HBM has the most contracted revenue. Toshiba's plan is a test of the first half of that bet.
Signposts
- Toshiba's follow-through. Whether its new capacity ships on schedule and at what prices.
- 2028 HBM contracts. Whether next year's agreements are signed at higher or lower prices than 2027's.
- NAND contract prices. Flash has the most new supply coming, so it should show the first price weakness if the cycle turns.
Data: SEC EDGAR XBRL filings and market prices, computed by StockResearch as of October 5, 2026. Forward P/E is consensus market data. Company figures come from the cited earnings releases and reports. Jake is the founder of StockResearch.app, where he writes data-first research on valuation dislocations. Nothing here is investment advice or a recommendation to buy or sell any security. Do your own research.