Gianluca Romano
Analyst · Cowen and Company
Thank you, Dave. Our September quarter results highlight solid growth across nearly all financial metrics and demonstrate site disciplined execution and ongoing focus on running profitability and free cash flow generation.
Revenue was $3.12 billion, up 3% sequentially. Non-GAAP operating margin expanded to 20.1% of revenue, up 200 basis points quarter-over-quarter, and non-GAAP EPS was $2.35, up 18% sequentially and at the high end of our guidance range. We grew total hard disk drive revenue to $2.9 billion, up 5% sequentially and 24% year-over-year. HDD capacity shipments increased 4% sequentially to 159 exabytes, up 39% relative to the prior year period.
Growth was driven by increasing demand for our mass capacity product, which contributed 71% of total HDD revenue and 83% of HDD exabyte shipments. Revenue from the mass capacity market increased to $2 billion, supported by growth across each of the underlying end markets, which include nearline, VIA and NAND products.
Mass capacity revenue was up 8% sequentially and up 51% compared with the prior year period, while capacity shipments into this market were up 7% sequentially and 53% year-over-year. Based on our current outlook, we expect mass capacity exabyte shipments to remain strong in the December quarter, with financial year '21 annual growth slightly above our long-term CAGR forecast of about 35%.
In the September quarter, nearline revenue demand was driven by improving enterprise spending and healthy growth from cloud data center customers. Nearline shipments totaled 106 exabytes, up 5% sequentially and 65% year-on-year, reflecting demand for our high capacity price, strong growth for dual actuator drive and ongoing market momentum for our common platform products spanning 16 through 20-terabyte price.
Robust demand in the bear market led to sequential revenue growth that was above the average for the mass capacity market, and we expect solid demand to continue in the December quarter. The legacy market made up the remaining 29% of HDD revenue, holding relatively stable at $821 million, down 3% sequentially and up 5% year-over-year.
Improving enterprise demand boosted sales for mission-critical drives, which partially offset the decline in consumer drives following a strong June quarter. We are starting to see a moderation in the pace of annual revenue decline following the significant market disruption brought on by the pandemic. While we could see some fluctuations in a given quarter, we believe the most pronounced impacts are behind us.
Finally, turning to our non-HDD business, Revenue came in at $151 million, down 9% sequentially of record June quarter level. Our systems business has been partially impacted by some of the supply constraints that Dave discussed. We are working closely with our suppliers to mitigate risk, and we continue to gain new customer wins to support longer-term growth in the business.
Overall, strong demand trends, combined with positive industry dynamics, led to non-GAAP gross profit of $966 million in the September quarter, up 8% sequentially and 57% year-over-year. Costs relating to freight and logistics are continuing to increment higher. While we will continue to take steps to reduce the impacts of these costs, we believe that we remain a headwind to the business through the fiscal year.
Our resulting non-GAAP gross margin expanded by about 140 basis points to 31%, well inside our long-term target range of 30% to 33%, including higher freight and logistic costs and component prices. HDD margins are now in the upper half of the range, reflecting better alignment in supply and demand and the transition to higher capacity drives. We anticipate continued solid gross margin performance with opportunity to increment higher, as we ramp our cost-optimized products. Additionally, as COVID cost headwinds abate, we would expect margins to expand into the upper half of our target range, over time.
Non-GAAP operating expenses decreased to $339 million, reflecting certain onetime savings. This is between expense management, combined with higher revenue and margin expansion, resulted in non-GAAP operating income of $627 million, up 15% sequentially and more than double the year ago period. Non-GAAP operating margin expanded to 20.1%, which is the top end of our long-term target range of 15% to 20% of revenue. Importantly, the September performance demonstrated our ability to grow profits faster than revenue, supporting our strategy of long-term value creation.
Based on diluted share count of approximately 231 million shares, non-GAAP EPS for the September quarter was $2.35, the highest level in close to a decade. We have the inventory relatively flat with the days inventory outstanding at 50 days. We are working with suppliers and managing strategic inventory levels to mitigate the risk to the business, while we continue to monitor with dynamic situation. Capital expenditures were $117 million for the quarter. We currently expect fiscal year CapEx to be at the low end of our long-term target range of 4% to 6% of revenue, which is sufficient to support our future product road map, while maintaining expense discipline.
Free cash flow generation increased to $379 million, up 7% quarter-over-quarter and more than double year-over-year. We delivered strong performance in the September quarter and expect to improve free cash flow generation through the fiscal year, enabling us to fund our growth opportunity and return capital to our shareholders. We used $153 million to fund the quarterly dividend and $425 million to repurchase 4.9 million ordinary shares, exiting the quarter with 225 million shares outstanding and approximately $3.8 billion remaining in our authorization.
As Dave mentioned earlier, the Board approved a $0.03 increase to our quarterly dividend raising the quarterly payout to $0.70 per share. We ended the September quarter with cash and cash equivalents of nearly $1 billion, and total liquidity was approximately $2.7 billion, including our revolving credit facility. Adjusted EBITDA was $724 million for the quarter and $2.4 billion for the 12-month period ending in September.
Total debt balance at the end of the quarter was $5.1 billion with a leverage ratio of 2.2x. In early October, we took advantage of the current attractive market environment to raise $725 million in capital through a new $600 million fixed year term loan and upsized our existing term loan during fiscal 2022. These actions are consistent with our growing business and provides the opportunity to repay $120 million in debt coming due in March. We reduced our average interest rate by 25 basis points and expect interest expenses for the December quarter to be approximately $66 million.
Looking ahead to our outlook for the December quarter. We anticipate a continuation of the strong demand environment that we experienced in the September quarter. We expect revenue to be in a range of $3.1 billion plus or minus $150 million. We expect non-GAAP operating margin to remain around the top end of our long-term range of 15% to 20% of revenue. And we expect non-GAAP EPS to be in the range of $2.35 plus or minus $0.15.
In summary, we had an outstanding September quarter, placing us on solid footing to deliver strong top and bottom line growth in calendar year 2021 as well as fiscal 2022. I will now turn the call back to Dave for final comments.