Exhibit 99.4

Dear Valued Partner,

As an important SanDisk partner, I am excited to share some important news with you.  Earlier today, we announced an agreement to be acquired by Western Digital.  A copy of the press release is available on SanDisk.com.

Joining forces with Western Digital builds on our 27-year legacy of innovative leadership in flash storage to create an even stronger partner.  Notably, this announcement does not change our current relationship with you.  Today’s announcement is just the first of many steps in the process, as the transaction is subject to closing conditions including regulatory approvals.

Until the transaction is completed, which we anticipate will occur in the third quarter 2016, SanDisk and Western Digital will continue to operate as independent companies.  That means that it is business as usual at SanDisk.

Our relationship with partners like you is of the utmost importance to us.  We will keep you informed as we work towards the completion of this transaction.  In the meantime, please do not hesitate to reach out to your SanDisk contact with any questions or concerns you may have.

Thank you for your continued partnership.

Best regards,

Sanjay

Sanjay Mehrotra

President and CEO
SanDisk Corporation

Forward Looking Statements

All statements included or incorporated by reference in this document, other than statements or characterizations of historical fact, are forward-looking statements within the meaning of the federal securities laws, including Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended.  These forward-looking statements are based on SanDisk’s current expectations, estimates and projections about its business and industry, management’s beliefs, and certain assumptions made by SanDisk and Western Digital, all of which are subject to change.  Forward-looking statements can often be identified by words such as “anticipates,” “expects,” “intends,” “plans,” “predicts,” “believes,” “seeks,” “estimates,” “may,” “will,” “should,” “would,” “could,” “potential,” “continue,” “ongoing,” similar expressions, and variations or negatives of these words.  Examples of such forward-looking statements include, but are not limited to, references to the anticipated benefits of the proposed merger and the expected date of closing of the merger.  These forward-looking statements are not guarantees of future results and are subject to risks, uncertainties and assumptions that could cause actual results to differ materially and adversely from those expressed in any forward-looking statement.

Important risk factors that may cause such a difference in connection with the proposed merger include, but are not limited to, the following factors: (1) the inability to complete the merger due to the failure to obtain stockholder approval for the merger or the failure to satisfy other conditions to completion of the merger, including the receipt of all regulatory approvals related to the merger; (2) uncertainties as to the timing of the consummation of the merger and the ability of each party to consummate the merger; (3) risks that the proposed merger disrupts the current plans and operations of Western Digital or SanDisk; (4) the ability of Western Digital and SanDisk to retain and hire key personnel; (5) competitive responses to the proposed merger; (6) unexpected costs, charges or expenses resulting from the merger; (7) the outcome of any legal proceedings that could be instituted against Western Digital, SanDisk or their respective directors related to the merger agreement; (8) potential adverse reactions or changes to business relationships resulting from the announcement or completion of the merger; (9) the inability to obtain, or delays in obtaining, cost savings and synergies from the merger; (10) delays, challenges and expenses associated with integrating the combined companies’ existing businesses and the indebtedness planned to be incurred in connection with the merger; and (11) legislative, regulatory and economic developments.  These risks, as well as other risks associated with the proposed merger, will be more fully discussed in the joint proxy statement/prospectus that will be included in the Registration Statement on Form S-4 that will be filed with the SEC in connection with the proposed merger.  The forward-looking statements in this document speak only as of this date.  Neither SanDisk nor Western Digital undertake any obligation to revise or update publicly any forward-looking statement to reflect future events or circumstances.

In addition, actual results are subject to other risks and uncertainties that relate more broadly to SanDisk’s overall business, including those more fully described in SanDisk’s filings with the Securities and Exchange Commission (“SEC”) including its annual report on Form 10-K for the fiscal year ended December 28, 2014, and its quarterly reports filed on Form 10-Q for the current fiscal year, and Western Digital’s overall business and financial condition, including those more fully described in Western Digital’s filings with the SEC including its annual report on Form 10-K for the fiscal year ended July 3, 2015.  The forward-looking statements in this document speak only as of date of this document.  We undertake no obligation to revise or update publicly any forward-looking statement, except as required by law.

Additional Information And Where To Find It

This communication does not constitute an offer to sell or the solicitation of an offer to buy any securities or a solicitation of any vote or approval nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. Western Digital will file with the SEC a Registration Statement on Form S-4 that will include a joint proxy statement/prospectus of SanDisk and Western Digital.  Each of SanDisk and Western Digital will provide the joint proxy statement/prospectus to their respective stockholders.  SanDisk and Western Digital also plan to file other documents with the SEC regarding the proposed merger.  This document is not a substitute for the joint proxy statement/prospectus or registration statement or any other document which SanDisk or Western Digital may file with the SEC in connection with the proposed merger.  INVESTORS AND SECURITY HOLDERS OF SANDISK AND WESTERN DIGITAL ARE URGED TO READ THE JOINT PROXY STATEMENT/PROSPECTUS AND ANY OTHER RELEVANT DOCUMENTS THAT WILL BE FILED WITH THE SEC CAREFULLY AND IN THEIR ENTIRETY WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT THE PROPOSED MERGER.  You may obtain copies of all documents filed with the SEC regarding this merger, free of charge, at the SEC’s website (www.sec.gov).  In addition, copies of the documents filed with the SEC by SanDisk will be available free of charge on SanDisk’s website at http://www.sandisk.com.  Copies of the documents filed with the SEC by Western Digital will be available free of charge on Western Digital’s website at http://www.westerndigital.com.

Participants in the Solicitation

SanDisk, Western Digital, and certain of their respective directors, executive officers and other members of management and employees, under SEC rules may be deemed to be participants in the solicitation of proxies from SanDisk and Western Digital stockholders in connection with the proposed merger.  You can find more detailed information about SanDisk’s executive officers and directors in its definitive proxy statement filed with the SEC on April 27, 2015.  You can find more detailed information about Western Digital’s executive officers and directors in its definitive proxy statement filed with the SEC on September 23, 2015.  Information regarding the persons who may, under the rules of the SEC, be deemed participants in the solicitation of stockholders in connection with the proposed merger will be set forth in the joint proxy statement/prospectus when it is filed with the SEC.  Additional information about SanDisk’s executive officers and directors and Western Digital’s executive officers and directors can be found in the joint proxy statement/prospectus regarding the proposed merger when it is filed with the SEC.