Western Digital Corporation
CH ˙ BRSE ˙ US9581021055
DETTE SYMBOL ER IKKE LÆNGERE AKTIVT
SecurityCH:12355 / Western Digital Corporation
InstitutionPrimecap Management Co/ca/
Latest Disclosed Ownership577,210 shares
Latest Disclosed Value $ 156,129,533
Primecap Management Co/ca/ reports 23.40% decrease in ownership of 12355 / Western Digital Corporation

On May 11, 2026 - Primecap Management Co/ca/ filed a 13F-HR form disclosing ownership of 577,210 shares of Western Digital Corporation (CH:12355) valued at $156,129,533 USD as of March 31, 2026. The entity filed a previous 13F-HR on February 11, 2026 disclosing 753,540 shares of Western Digital Corporation. This represents a change in shares of -23.40% during the quarter.

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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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)
2026-05-11 2026-03-31 13F WESTERN DIGITAL COM 958102105 577,210 -176,330 -23.40 156,130 20.27 0.1229
2026-02-11 2025-12-31 13F WESTERN DIGITAL COM 958102105 753,540 -211,530 -21.92 129,812 12.04 0.0983
2025-11-12 2025-09-30 13F WESTERN DIGITAL COM 958102105 965,070 -107,020 -9.98 115,866 68.89 0.0887
2025-08-11 2025-06-30 13F WESTERN DIGITAL COM 958102105 1,072,090 -49,465 -4.41 68,603 51.29 0.0544
2025-05-09 2025-03-31 13F WESTERN DIGITAL COM 958102105 1,121,555 -37,060 -3.20 45,344 -34.37 0.0375
2025-02-10 2024-12-31 13F WESTERN DIGITAL COM 958102105 1,158,615 -2,820 -0.24 69,088 -12.89 0.0535
2024-11-08 2024-09-30 13F WESTERN DIGITAL COM 958102105 1,161,435 -34,690 -2.90 79,314 -12.49 0.0583
2024-08-09 2024-06-30 13F WESTERN DIGITAL COM 958102105 1,196,125 -79,763 -6.25 90,630 4.09 0.0656
2024-05-14 2024-03-31 13F WESTERN DIGITAL COM 958102105 1,275,888 -266,720 -17.29 87,067 7.77 0.0649
2024-02-09 2023-12-31 13F WESTERN DIGITAL COM 958102105 1,542,608 -736,761 -32.32 80,786 -22.33 0.0640
2023-11-13 2023-09-30 13F WESTERN DIGITAL COM 958102105 2,279,369 -7,607 -0.33 104,008 19.90 0.0878
2023-08-11 2023-06-30 13F WESTERN DIGITAL COM 958102105 2,286,976 -128,100 -5.30 86,745 -4.65 0.0725
2023-05-15 2023-03-31 13F WESTERN DIGITAL COM 958102105 2,415,076 -278,528 -10.34 90,976 7.05 0.0793
2023-02-13 2022-12-31 13F WESTERN DIGITAL COM 958102105 2,693,604 70,150 2.67 84,983 -0.48 0.0778
2022-11-14 2022-09-30 13F WESTERN DIGITAL COM 958102105 2,623,454 331,875 14.48 85,393 -16.88 0.0826
2022-08-11 2022-06-30 13F WESTERN DIGITAL COM 958102105 2,291,579 231,969 11.26 102,731 0.46 0.0918
2022-05-11 2022-03-31 13F WESTERN DIGITAL COM 958102105 2,059,610 49,663 2.47 102,260 -21.98 0.0771
2022-02-11 2021-12-31 13F WESTERN DIGITAL COM 958102105 2,009,947 212,280 11.81 131,069 29.18 0.0907
2021-11-12 2021-09-30 13F WESTERN DIGITAL COM 958102105 1,797,667 218,240 13.82 101,460 -9.74 0.0716
2021-08-10 2021-06-30 13F WESTERN DIGITAL COM 958102105 1,579,427 -8,060 -0.51 112,408 6.08 0.0755
2021-05-14 2021-03-31 13F WESTERN DIGITAL COM 958102105 1,587,487 21,180 1.35 105,965 22.14 0.0739
2021-02-08 2020-12-31 13F WESTERN DIGITAL COM 958102105 1,566,307 257,500 19.67 86,758 81.36 0.0645
2020-11-13 2020-09-30 13F WESTERN DIGITAL COM 958102105 1,308,807 716,900 121.12 47,837 83.05 0.0395
2020-08-13 2020-06-30 13F WESTERN DIGITAL COM 958102105 591,907 104,770 21.51 26,133 28.89 0.0224
2020-05-14 2020-03-31 13F WESTERN DIGITAL COM 958102105 487,137 -359,949 -42.49 20,275 -62.29 0.0199
2020-02-14 2019-12-31 13F WESTERN DIGITAL COM 958102105 847,086 3,314 0.39 53,765 6.84 0.0390
2019-11-13 2019-09-30 13F WESTERN DIGITAL COM 958102105 843,772 -200,864 -19.23 50,323 1.31 0.0402
2019-08-14 2019-06-30 13F WESTERN DIGITAL COM 958102105 1,044,636 298,256 39.96 49,672 38.47 0.0367
2019-05-14 2019-03-31 13F WESTERN DIGITAL COM 958102105 746,380 222,050 42.35 35,871 85.05 0.0264
2019-02-12 2018-12-31 13F WESTERN DIGITAL COM 958102105 524,330 -150,183 -22.27 19,384 -50.91 0.0157
2018-11-13 2018-09-30 13F WESTERN DIGITAL COM 958102105 674,513 -47,413 -6.57 39,486 -29.34 0.0267
2018-08-13 2018-06-30 13F WESTERN DIGITAL COM 958102105 721,926 -6,643 -0.91 55,884 -16.87 0.0414
2018-05-14 2018-03-31 13F WESTERN DIGITAL COM 958102105 728,569 -144,137 -16.52 67,225 -3.14 0.0504
2018-02-13 2017-12-31 13F WESTERN DIGITAL COM 958102105 872,706 -197,137 -18.43 69,406 -24.91 0.0533
2017-11-13 2017-09-30 13F WESTERN DIGITAL COM 958102105 1,069,843 -54,253 -4.83 92,434 -7.19 0.0765
2017-08-11 2017-06-30 13F WESTERN DIGITAL COM 958102105 1,124,096 -10,688 -0.94 99,595 6.34 0.0856
2017-05-12 2017-03-31 13F WESTERN DIGITAL COM 958102105 1,134,784 -10,387 -0.91 93,654 20.36 0.0850
2017-02-13 2016-12-31 13F WESTERN DIGITAL COM 958102105 1,145,171 -32,657 -2.77 77,814 12.99 0.0766
2016-11-14 2016-09-30 13F WESTERN DIGITAL COM 958102105 1,177,828 -114,996 -8.89 68,868 12.72 0.0687
2016-08-12 2016-06-30 13F WESTERN DIGITAL COM 958102105 1,292,824 1,292,824 61,099 0.0651
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.