Western Digital Corporation
CH ˙ BRSE ˙ US9581021055
DETTE SYMBOL ER IKKE LÆNGERE AKTIVT
SecurityCH:12355 / Western Digital Corporation
InstitutionMaple Rock Capital Partners Inc.
Latest Disclosed Ownership1,400,434 shares
Latest Disclosed Value $ 378,803,393
Maple Rock Capital Partners Inc. ownership in 12355 / Western Digital Corporation

On May 15, 2026 - Maple Rock Capital Partners Inc. filed a 13F-HR form disclosing ownership of 1,400,434 shares of Western Digital Corporation (CH:12355) valued at $378,803,393 USD as of March 31, 2026. The entity filed a previous 13F-HR on February 17, 2026 disclosing 2,381,525 shares of Western Digital Corporation. This represents a change in shares of -41.20% during the quarter.

Maple Rock Capital Partners Inc. has a history of taking positions in derivatives of the underlying security (12355) in the form of stock options. The firm currently holds call options representing 0 of underlying shares valued at $0 USD .

Note: prior versions of this page mistakenly stated that the share values represented the number of options, not the number of underlying shares. For more information on the data backing these reports, please see the SEC document Frequently Asked Questions About Form 13F.

Institutional Ownership: 13F and NPORT Filings

The Security and Class in the table below are shown exactly as filed by the investor. We do our best to track continuity of investments through acquisitions, and this will be reflected in the table as changes in names. In addition to descriptive data, performance of the investment is shown over time. To calculate quarterly performance, we first calculate cost basis of the shares purchased during the quarter, then use that to calculate gross profit. Quarterly return is Gross Profit / Starting Portfolio value.

Note that cost basis is calculated and stored in thousands, so small quarterly changes in shares frequently result in a cost basis of zero.

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Institutional Put/Call Ratios
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In addition to reporting standard equity and debt issues, institutions with more than 100MM assets under management must also disclose their put and call option holdings. Since put options generally indicate negative sentiment, and call options indicate positive sentiment, we can get a sense of the overall institutional sentiment by plotting the ratio of puts to calls. The chart to the right plots the historical put/call ratio for this instrument.

Using Put/Call Ratio as an indicator of investor sentiment overcomes one of the key deficiencies of using total institutional ownership, which is that a significant amount of assets under management are invested passively to track indices. Passively-managed funds do not typically buy options, so the put/call ratio indicator more closely tracks the sentiment of actively-managed funds.

CH:12355 / Western Digital Corporation Historical Put/Call Ratio
Disclosed Equity Positions (from 13F/NPORT Filings)
File
Date
Effective
Date
Form Security Class ID Avg Price
Paid (Est)
Reported
Shares
ΔShares ΔShares
(%)
Reported
Value
(x1000)
ΔValue
(%)
Alloc
(%)
ΔAlloc ΔAlloc (%) Cost Basis
(x1000)
Unrealized
Gain/Loss
(x1000)
2026-05-15 2026-03-31 13F WESTERN DIGITAL COM 958102105 1,400,434 -981,091 -41.20 378,803 -7.67 12.3249
2026-02-17 2025-12-31 13F WESTERN DIGITAL COM 958102105 2,381,525 -207,800 -8.03 410,265 31.97 13.5529
2025-11-14 2025-09-30 13F WESTERN DIGITAL COM 958102105 2,589,325 -1,145,971 -30.68 310,874 30.06 12.2675
2025-08-14 2025-06-30 13F WESTERN DIGITAL COM 958102105 3,735,296 545,500 17.10 239,022 85.34 11.7133
2025-05-15 2025-03-31 13F WESTERN DIGITAL COM 958102105 3,189,796 205,896 6.90 128,963 -27.52 4.7221
2025-02-14 2024-12-31 13F WESTERN DIGITAL COM 958102105 2,983,900 -303,500 -9.23 177,930 -20.74 5.3420
2024-11-14 2024-09-30 13F WESTERN DIGITAL COM 958102105 3,287,400 383,390 13.20 224,497 2.03 6.3534
2024-08-14 2024-06-30 13F WESTERN DIGITAL COM 958102105 2,904,010 0 0.00 220,037 11.03 7.4582
2024-05-15 2024-03-31 13F WESTERN DIGITAL COM 958102105 2,904,010 68,340 2.41 198,170 33.44 10.9836
2024-02-14 2023-12-31 13F WESTERN DIGITAL COM 958102105 2,835,670 349,337 14.05 148,504 30.90 8.4597
2023-11-14 2023-09-30 13F WESTERN DIGITAL COM 958102105 2,486,333 563,232 29.29 113,451 55.53 9.9792
2023-08-14 2023-06-30 13F WESTERN DIGITAL COM 958102105 1,923,101 -121,000 -5.92 72,943 -5.27 5.9397
2023-05-15 2023-03-31 13F WESTERN DIGITAL COM 958102105 2,044,101 98,200 5.05 77,001 25.42 6.7956
2023-02-14 2022-12-31 13F WESTERN DIGITAL COM 958102105 1,945,901 -296,299 -13.21 61,393 -15.88 2.4811
2022-11-14 2022-09-30 13F WESTERN DIGITAL COM 958102105 2,242,200 926,500 70.42 72,984 23.74 3.4858
2022-08-15 2022-06-30 13F WESTERN DIGITAL COM 958102105 1,315,700 146,000 12.48 58,983 1.56 3.4371
2022-05-16 2022-03-31 13F WESTERN DIGITAL COM 958102105 1,169,700 366,700 45.67 58,076 10.91 3.0976
2022-02-14 2021-12-31 13F WESTERN DIGITAL COM 958102105 803,000 106,000 15.21 52,364 33.11 5.5921
2021-11-15 2021-09-30 13F WESTERN DIGITAL COM 958102105 697,000 -329,000 -32.07 39,339 -46.13 5.5106
2021-08-16 2021-06-30 13F WESTERN DIGITAL COM 958102105 1,026,000 -54,000 -5.00 73,020 1.29 10.9754
2021-05-17 2021-03-31 13F WESTERN DIGITAL COM 958102105 1,080,000 410,000 61.19 72,090 94.26 10.4599
2021-02-16 2020-12-31 13F WESTERN DIGITAL COM 958102105 670,000 -233,000 -25.80 37,111 12.44 5.3834
2020-11-16 2020-09-30 13F WESTERN DIGITAL COM 958102105 903,000 767,917 568.48 33,005 453.40 6.0304
2020-08-14 2020-06-30 13F WESTERN DIGITAL COM 958102105 135,083 -185,000 -57.80 5,964 -55.23 1.1936
2020-05-15 2020-03-31 13F WESTERN DIGITAL COM 958102105 320,083 -337,917 -51.36 13,322 -68.10 3.4167
2020-02-14 2019-12-31 13F WESTERN DIGITAL COM 958102105 658,000 -107,000 -13.99 41,763 -8.46 6.3562
2019-11-14 2019-09-30 13F WESTERN DIGITAL COM 958102105 765,000 0 0.00 45,625 25.43 6.1156
2019-08-14 2019-06-30 13F WESTERN DIGITAL COM 958102105 765,000 650,000 565.22 36,376 558.15 6.0198
2019-05-15 2019-03-31 13F WESTERN DIGITAL COM 958102105 115,000 115,000 5,527 1.6224
2017-11-14 2017-09-30 13F WESTERN DIGITAL COM 958102105 0 -250,000 -100.00 0 -100.00
2017-08-14 2017-06-30 13F WESTERN DIGITAL COM 958102105 250,000 -125,000 -33.33 22,150 -28.43 6.8202
2017-05-15 2017-03-31 13F WESTERN DIGITAL COM 958102105 375,000 -100,000 -21.05 30,948 -4.11 6.3527
2017-02-14 2016-12-31 13F WESTERN DIGITAL COM 958102105 475,000 125,000 35.71 32,276 57.71 10.8627
2016-11-14 2016-09-30 13F WESTERN DIGITAL COM 958102105 350,000 350,000 20,465 7.7454
Disclosed Call Options
File
Date
Effective
Date
Form Security Class ID Opt Avg Share
Price
Shares ΔShares
(%)
Value
(x1000)
ΔValue
(%)
Prior Allocation
(%)
Allocation
(%)
ΔAllocation
(%)
Cost Basis
(x1000)
Profit
(x1000)
Return
(%)
2024-08-14 2024-06-30 13F WESTERN DIGITAL COM Call 0 -100.00 0 -100.00 n/a n/a n/a
2024-05-15 2024-03-31 13F WESTERN DIGITAL COM Call 1,500,000 -25.00 102,360 -2.27 n/a n/a n/a
2024-02-14 2023-12-31 13F WESTERN DIGITAL COM Call 2,000,000 104,740 n/a n/a n/a
2021-05-17 2021-03-31 13F WESTERN DIGITAL COM Call 0 -100.00 0 -100.00 n/a n/a n/a
2021-02-16 2020-12-31 13F WESTERN DIGITAL COM Call 2,005,100 101.46 111,062 205.30 n/a n/a n/a
2020-11-16 2020-09-30 13F WESTERN DIGITAL COM Call 995,300 36,378 n/a n/a n/a
2020-05-15 2020-03-31 13F WESTERN DIGITAL COM Call 0 -100.00 0 -100.00 n/a n/a n/a
2020-02-14 2019-12-31 13F WESTERN DIGITAL COM Call 2,447,200 -33.73 155,324 -29.48 n/a n/a n/a
2019-11-14 2019-09-30 13F WESTERN DIGITAL COM Call 3,693,000 10.24 220,251 38.27 n/a n/a n/a
2019-08-14 2019-06-30 13F WESTERN DIGITAL COM Call 3,350,000 159,293 n/a n/a n/a
2017-08-14 2017-06-30 13F WESTERN DIGITAL COM Call 0 -100.00 0 -100.00 n/a n/a n/a
2017-05-15 2017-03-31 13F WESTERN DIGITAL COM Call 1,354,500 16,119.61 111,786 10,366.85 n/a n/a n/a
2017-02-14 2016-12-31 13F WESTERN DIGITAL CALL Call 8,351 25.09 1,068 -20.48 n/a n/a n/a
2016-11-14 2016-09-30 13F WESTERN DIGITAL COM Call 6,676 1,343 n/a n/a n/a
Legend
Shares
The total number of shares held by the institution at the end of the reporting period (the effective date). This is provided in the filing.
Value
The total value of the shares as of the effective date. This is provided in the filing.
Avg. Share Price
The weighted average share price of the shares held by the institution. We use FIFO accounting to determine this price
Class
This is the security class as indicated by the filer. There are a variety of values for this field. Common values include "EC" = equity common, "EP" - equity preferred
Allocation (%)
The percent of the institution's portfolio that this position represents. This is provided in NPORT filings. For 13F filings, we calculate it.
Change in Allocation
The change in allocation from the prior reporting period. This is calculated as current allocation - prior allocation.
Change in Allocation (%)
The percent change in allocation from the prior reporting period. This is calculated as (current allocation - prior allocation) / prior allocation.
Cost Basis
The total cost of the shares held. This is calculated as reported shares * avg. share price
Unrealized Gain/Loss
This is the market value of the position as of the effective date minus the cost basis.