Western Digital Corporation
CH ˙ BRSE ˙ US9581021055
DETTE SYMBOL ER IKKE LÆNGERE AKTIVT
SecurityCH:12355 / Western Digital Corporation
InstitutionBlair William & Co/il
Latest Disclosed Ownership22,491 shares
Latest Disclosed Value $ 6,083,603
Blair William & Co/il ownership in 12355 / Western Digital Corporation

On May 8, 2026 - Blair William & Co/il filed a 13F-HR form disclosing ownership of 22,491 shares of Western Digital Corporation (CH:12355) valued at $6,083,603 USD as of March 31, 2026. The entity filed a previous 13F-HR on February 17, 2026 disclosing 18,919 shares of Western Digital Corporation. This represents a change in shares of 18.88% during the quarter.

Blair William & Co/il 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)
2026-05-08 2026-03-31 13F WESTERN DIGITAL COM 958102105 22,491 3,572 18.88 6,084 86.65 0.0174
2026-02-17 2025-12-31 13F WESTERN DIGITAL COM 958102105 18,919 -218 -1.14 3,259 41.88 0.0087
2025-11-12 2025-09-30 13F WESTERN DIGITAL COM 958102105 19,137 -265 -1.37 2,298 85.09 0.0061
2025-07-24 2025-06-30 13F WESTERN DIGITAL COM 958102105 19,402 -121 -0.62 1,242 57.29 0.0034
2025-05-09 2025-03-31 13F WESTERN DIGITAL COM 958102105 19,523 399 2.09 789 -30.79 0.0024
2025-02-12 2024-12-31 13F WESTERN DIGITAL COM 958102105 19,124 236 1.25 1,140 -11.56 0.0033
2024-11-12 2024-09-30 13F WESTERN DIGITAL COM 958102105 18,888 -382 -1.98 1,290 -11.71 0.0038
2024-08-12 2024-06-30 13F WESTERN DIGITAL COM 958102105 19,270 1,375 7.68 1,460 19.57 0.0045
2024-05-09 2024-03-31 13F WESTERN DIGITAL COM 958102105 17,895 -1,429 -7.39 1,221 20.77 0.0038
2024-02-12 2023-12-31 13F WESTERN DIGITAL COM 958102105 19,324 99 0.51 1,012 15.28 0.0034
2023-11-09 2023-09-30 13F WESTERN DIGITAL COM 958102105 19,225 1,430 8.04 877 30.12 0.0034
2023-08-11 2023-06-30 13F WESTERN DIGITAL COM 958102105 17,795 -1,737 -8.89 675 -8.30 0.0025
2023-05-12 2023-03-31 13F WESTERN DIGITAL COM 958102105 19,532 -881 -4.32 736 14.13 0.0029
2023-02-10 2022-12-31 13F WESTERN DIGITAL COM 958102105 20,413 -1,616 -7.34 644 -10.18 0.0028
2022-11-09 2022-09-30 13F WESTERN DIGITAL COM 958102105 22,029 -3,386 -13.32 717 -37.05 0.0033
2022-08-10 2022-06-30 13F WESTERN DIGITAL COM 958102105 25,415 -2,533 -9.06 1,139 -17.94 0.0051
2022-05-13 2022-03-31 13F WESTERN DIGITAL COM 958102105 27,948 -476 -1.67 1,388 -25.13 0.0049
2022-02-14 2021-12-31 13F WESTERN DIGITAL COM 958102105 28,424 7,077 33.15 1,854 53.86 0.0058
2021-11-12 2021-09-30 13F WESTERN DIGITAL COM 958102105 21,347 8,224 62.67 1,205 29.01 0.0041
2021-08-12 2021-06-30 13F WESTERN DIGITAL COM 958102105 13,123 1,166 9.75 934 17.04 0.0032
2021-05-13 2021-03-31 13F WESTERN DIGITAL COM 958102105 11,957 595 5.24 798 26.87 0.0030
2021-02-09 2020-12-31 13F WESTERN DIGITAL COM 958102105 11,362 3,832 50.89 629 128.73 0.0023
2020-11-06 2020-09-30 13F WESTERN DIGITAL COM 958102105 7,530 584 8.41 275 -10.42 0.0012
2020-08-12 2020-06-30 13F WESTERN DIGITAL COM 958102105 6,946 -315 -4.34 307 1.66 0.0015
2020-05-11 2020-03-31 13F WESTERN DIGITAL COM 958102105 7,261 -1,121 -13.37 302 -43.23 0.0019
2020-02-13 2019-12-31 13F WESTERN DIGITAL COM 958102105 8,382 687 8.93 532 15.90 0.0027
2019-11-12 2019-09-30 13F WESTERN DIGITAL COM 958102105 7,695 729 10.47 459 38.67 0.0026
2019-08-13 2019-06-30 13F WESTERN DIGITAL COM 958102105 6,966 1,282 22.55 331 21.25 0.0019
2019-05-14 2019-03-31 13F WESTERN DIGITAL COM 958102105 5,684 5,684 273 0.0017
2018-11-13 2018-09-30 13F WESTERN DIGITAL COM 958102105 0 -3,081 -100.00 0 -100.00
2018-08-13 2018-06-30 13F WESTERN DIGITAL COM 958102105 3,081 -591 -16.09 239 -29.50 0.0016
2018-05-15 2018-03-31 13F WESTERN DIGITAL COM 958102105 3,672 -1,627 -30.70 339 -19.48 0.0024
2018-02-14 2017-12-31 13F WESTERN DIGITAL COM 958102105 5,299 -2,609 -32.99 421 -38.36 0.0029
2017-11-13 2017-09-30 13F WESTERN DIGITAL COM 958102105 7,908 -2,783 -26.03 683 -27.88 0.0051
2017-08-04 2017-06-30 13F WESTERN DIGITAL COM 958102105 10,691 1,628 17.96 947 35.87 0.0071
2017-05-10 2017-03-31 13F WESTERN DIGITAL COM 958102105 9,063 -1,437 -13.69 697 -2.24 0.0056
2017-02-14 2016-12-31 13F WESTERN DIGITAL COM 958102105 10,500 3,447 48.87 713 73.06 0.0064
2016-11-14 2016-09-30 13F WESTERN DIGITAL ADR 958102105 7,053 2,658 60.48 412 98.08 0.0036
2016-08-08 2016-06-30 13F Western Digital ADR 958102105 4,395 -892 -16.87 208 -16.47 0.0019
2016-05-16 2016-03-31 13F WESTERN DIGITAL COM 958102105 5,287 -2,382 -31.06 249 -45.87 0.0023
2016-02-16 2015-12-31 13F WESTERN DIGITAL COM 958102105 7,669 7,669 460 0.0043
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
(%)
2017-08-04 2017-06-30 13F WESTERN DIGITAL OPTION Call 0 -100.00 0 -100.00 n/a n/a n/a
2017-05-10 2017-03-31 13F WESTERN DIGITAL OPTION Call 500 0.00 41 20.59 n/a n/a n/a
2017-02-14 2016-12-31 13F WESTERN DIGITAL OPTION Call 500 34 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.