Exhibit 99.1

THIS DOCUMENT IS IMPORTANT AND REQUIRES YOUR IMMEDIATE ATTENTION. If you are in any doubt as to the action to be taken, you should immediately consult your broker, bank manager, lawyer, accountant, investment advisor or other professional adviser.

LETTER OF TRANSMITTAL

Relating to

Western Digital Corporation

Offer to exchange any and all of Western Digital Corporation’s outstanding unregistered 10.500% Senior Notes due 2024 (CUSIP Nos. 958102 AK1 and U9547K AB9) for $3,350.0 million aggregate principal amount of its new 10.500% Senior Notes due 2024 (CUSIP No. 958102 AL9) that have been registered under the Securities Act of 1933, as amended (the “Securities Act”)

This document relates to the exchange offer (the “Exchange Offer”) made by Western Digital Corporation (the “Issuer”) to exchange any and all of its unregistered $3,350.0 million 10.500% Senior Notes due 2024 (the “Old Notes”) for new 10.500% Senior Notes due 2024 (the “New Notes”) that have been registered under the Securities Act. The Old Notes and the New Notes are collectively referred to herein as the “Notes.” The Exchange Offer is described in the Prospectus dated                 , 2017 (the “Prospectus”) and in this letter of transmittal (this “Letter of Transmittal”). All terms and conditions contained in, or otherwise referred to in, the Prospectus are deemed to be incorporated in, and form a part of, this Letter of Transmittal. Therefore you are urged to read carefully the Prospectus and the items referred to therein. The terms and conditions contained in the Prospectus, together with the terms and conditions governing this Letter of Transmittal and the instructions herein, are collectively referred to herein as the “terms and conditions.”

The Exchange Offer will expire at 5:00 p.m., New York City time, on                 , 2017, unless extended by the Issuer (such date and time, as they may be extended, the “Expiration Date”). Tendered Old Notes may be withdrawn at any time prior to the expiration of the Exchange Offer.

Upon the satisfaction or waiver of the conditions to the acceptance of the Old Notes set forth in the Prospectus under “Description of the Exchange Offer—Conditions to the Exchange Offer,” the Issuer will accept for settlement the Old Notes that have been validly tendered (and not subsequently validly withdrawn). This acceptance date is referred to as the “Acceptance Date.” The Issuer will deliver the New Notes on a date (the “Settlement Date”) as soon as practicable after the Expiration Date.

The Exchange Agent for the Exchange Offer is:

U.S. Bank National Association

For Delivery by Hand, Overnight

Delivery,

Registered or Certified Mail:

U.S. Bank National Association

Global Corporate Trust Services

111 Fillmore Ave. East, EP-MN-

WS2N

St. Paul, MN 55107

Attention: Specialized Finance

or

By Facsimile Transmission:

(651)466-7372

Attention: Specialized Finance

or

By Telephone:

(800) 934-6802

This Letter of Transmittal is to be used by holders of the Old Notes. Tender of the Old Notes is to be made using the Automated Tender Offer Program (“ATOP”) of The Depository Trust Company (“DTC”) pursuant to the procedures set forth in the Prospectus under the caption “Description of the Exchange Offer—Procedures for Tendering.” DTC participants that are accepting the Exchange Offer must transmit their acceptance to DTC, which will verify the acceptance and execute a book-entry delivery to the Exchange Agent’s DTC account. DTC will then send a computer-generated message known as an “agent’s message” to the Exchange Agent for its acceptance. For you to validly tender your Old Notes in the Exchange Offer, the Exchange Agent must receive, prior to the Expiration Date, an agent’s message under the ATOP procedures that confirms that:

• DTC has received your instructions to tender your Old Notes; and

• You agree to be bound by the terms of this Letter of Transmittal.

By using the ATOP procedures to tender the Old Notes, you will not be required to deliver this Letter of Transmittal to the Exchange Agent. However, you will be bound by its terms, and you will be deemed to have made the acknowledgments and the representations and warranties it contains, just as if you had signed it.

The New Notes will be issued in full exchange for the Old Notes in the Exchange Offer, if consummated, on the Settlement Date and will be delivered in book-entry form.

Please read the accompanying instructions carefully.

Ladies and Gentlemen:

Upon the terms and subject to the conditions of the Exchange Offer, the undersigned hereby tenders to the Issuer the aggregate principal amount of Old Notes credited by the undersigned to the Exchange Agent’s account at DTC using ATOP.

The undersigned understands that validly tendered Old Notes (or defectively tendered Old Notes with respect to which the Issuer has waived such defect or caused such defect to be waived) will be deemed to have been accepted by the Issuer if, as and when the Issuer gives oral or written notice thereof to the Exchange Agent. The undersigned understands that, subject to the terms and conditions, the Old Notes properly tendered and accepted (and not validly withdrawn) in accordance with the terms and conditions will be exchanged for the New Notes. The undersigned understands that, under certain circumstances, the Issuer may not be required to accept any of the Old Notes tendered (including any such Old Notes tendered after the Expiration Date). If any Old Notes are not accepted for exchange for any reason (or if the Old Notes are validly withdrawn), such Old Notes will be returned, without expense, to the undersigned’s account at DTC or such other account as designated herein, pursuant to the book-entry transfer procedures described in the Prospectus, as promptly as practicable after the expiration or termination of the Exchange Offer.

By tendering the Old Notes in the Exchange Offer, the undersigned acknowledges that the Exchange Offer is being made based upon the Issuer’s understanding of an interpretation by the staff of the Securities and Exchange Commission (the “SEC”) as set forth in no-action letters issued to other parties, including Exxon Capital Holdings Corporation, SEC No-Action Letter (available May 13, 1988), Morgan Stanley & Co. Incorporated, SEC No-Action Letter (available June 5, 1991) and Shearman & Sterling, SEC No-Action Letter (available July 2, 1993), that the New Notes issued in exchange for the Old Notes pursuant to the Exchange Offer may be offered for resale, resold and otherwise transferred by each holder thereof (other than a broker-dealer who acquires such New Notes directly from the Issuer for resale pursuant to Rule 144A under the Securities Act or any other available exemption under the Securities Act or any such holder that is an “affiliate” of the Issuer within the meaning of Rule 405 under the Securities Act), without compliance with the registration and prospectus delivery provisions of the Securities Act, provided that such New Notes are acquired in the ordinary course of such holder’s business and such holder is not engaged in, and does not intend to engage in, a distribution of such New Notes and has no arrangement with any person to participate in the distribution of such New Notes. If the undersigned is not a broker-dealer, the undersigned represents that it acquires the New Notes in the ordinary course of its business, it is not engaged in, and does not intend to engage in, a distribution of the New Notes and it has no arrangements or understandings with any person to participate in a distribution of the New Notes. If the undersigned is a broker-dealer that will receive the New Notes for its own account in exchange for the Old Notes, it represents that the Old Notes to be exchanged for the New Notes were acquired by it as a result of market-making activities or other trading activities and acknowledges that it will deliver a prospectus in connection with any resale of such New Notes; however, by so acknowledging and by delivering a prospectus, the undersigned will not be deemed to admit that it is an “underwriter” within the meaning of the Securities Act.

Upon agreement to the terms of this Letter of Transmittal pursuant to an agent’s message, the undersigned, or the beneficial holder of the Old Notes on behalf of which the undersigned has tendered, will, subject to that holder’s ability to withdraw its tender, and subject to the terms and conditions of the Exchange Offer generally, hereby:

• irrevocably sell, assign and transfer to or upon the order of the Issuer or its nominee all right, title and interest in and to, and any and all claims in respect of or arising or having arisen as a result of the undersigned’s status as a holder of, all Old Notes tendered hereby, such that thereafter it shall have no contractual or other rights or claims in law or equity against the Issuer or any fiduciary, trustee, fiscal agent or other person connected with the Old Notes arising under, from or in connection with such Old Notes;

• waive any and all rights with respect to the Old Notes tendered hereby, including, without limitation, any existing or past defaults and their consequences in respect of such Old Notes; and

• release and discharge the Issuer, the Guarantors and U.S. Bank National Association, as the trustee for the Old Notes from any and all claims the undersigned may have, now or in the future, arising out of or related to the Old Notes tendered hereby, including, without limitation, any claims that the undersigned is entitled to receive additional principal or interest payments with respect to the Old Notes tendered hereby, other than as expressly provided in the Prospectus and in this Letter of Transmittal, or to participate in any redemption or defeasance of the Old Notes tendered hereby.

The undersigned understands that tenders of the Old Notes pursuant to the procedures described in the Prospectus and in this Letter of Transmittal and acceptance of such Old Notes by the Issuer will, following such acceptance, constitute a binding agreement between the undersigned and the Issuer upon the terms and conditions.

By tendering the Old Notes in the Exchange Offer, the undersigned represents, warrants and agrees that:

• it has received the Prospectus;

• it is the beneficial owner (as defined below) of, or a duly authorized representative of one or more beneficial owners of, the Old Notes tendered hereby, and it has full power and authority to execute this Letter of Transmittal;

• the Old Notes being tendered hereby were owned as of the date of tender, free and clear of any liens, charges, claims, encumbrances, interests and restrictions of any kind, and the Issuer will acquire good, indefeasible and unencumbered title to such Old Notes, free and clear of all liens, charges, claims, encumbrances, interests and restrictions of any kind, when the Issuer accepts the same;

• it will not sell, pledge, hypothecate or otherwise encumber or transfer any Old Notes tendered hereby from the date of this Letter of Transmittal, and any purported sale, pledge, hypothecation or other encumbrance or transfer will be void and of no effect;

• in evaluating the Exchange Offer and in making its decision whether to participate in the Exchange Offer by tendering its Old Notes, the undersigned has made its own independent appraisal of the matters referred to in the Prospectus and this Letter of Transmittal and in any related communications and it is not relying on any statement, representation or warranty, express or implied, made to such holder by the Issuer or the Exchange Agent, other than those contained in the Prospectus, as amended or supplemented through the Expiration Date;

• the execution and delivery of this Letter of Transmittal shall constitute an undertaking to execute any further documents and give any further assurances that may be required in connection with any of the foregoing, in each case on and subject to the terms and conditions described or referred to in the Prospectus;

• the agreement to the terms of this Letter of Transmittal pursuant to an agent’s message shall, subject to the terms and conditions of the Exchange Offer, constitute the irrevocable appointment of the Exchange Agent as its attorney and agent and an irrevocable instruction to such attorney and agent to complete and execute all or any forms of transfer and other documents at the discretion of that attorney and agent in relation to the Old Notes tendered hereby in favor of the Issuer or any other person or persons as the Issuer may direct and to deliver such forms of transfer and other documents in the attorney’s and agent’s discretion and the certificates and other documents of title relating to the registration of such Old Notes and to execute all other documents and to do all other acts and things as may be in the opinion of that attorney or agent necessary or expedient for the purpose of, or in connection with, the acceptance of the Exchange Offer, and to vest in the Issuer or their nominees such Old Notes;

• the terms and conditions of the Exchange Offer shall be deemed to be incorporated in, and form a part of, this Letter of Transmittal, which shall be read and construed accordingly;

• it is acquiring the New Notes in the ordinary course of its business;

• it is not participating in, and does not intend to participate in, a distribution of the New Notes within the meaning of the Securities Act and has no arrangement or understanding with any person to participate in a distribution of the New Notes within the meaning of the Securities Act;

• it is not a broker-dealer who acquired the Old Notes directly from the Issuer; and

• it is not an “affiliate” of the Issuer, within the meaning of Rule 405 of the Securities Act.

The representations, warranties and agreements of a holder tendering the Old Notes shall be deemed to be repeated and reconfirmed on and as of the Expiration Date and the Settlement Date. For purposes of this Letter of Transmittal, the “beneficial owner” of any Old Notes means any holder that exercises investment discretion with respect to such Old Notes.

The undersigned understands that tenders may not be withdrawn at any time after the Expiration Date, except as set forth in the Prospectus, unless the Exchange Offer is amended with changes to the terms and conditions that are, in the reasonable judgment of the Issuer, materially adverse to the tendering holders, in which case tenders may be withdrawn under the conditions described in the extension.

If the Exchange Offer is amended in a manner determined by the Issuer to constitute a material change, the Issuer will extend the Exchange Offer for a period of two to ten business days, depending on the significance of the amendment and the manner of disclosure to such holders, if the Exchange Offer would otherwise have expired during such two to ten business day period.

All authority conferred or agreed to be conferred in this Letter of Transmittal and every obligation of the undersigned hereunder shall be binding upon the undersigned’s successors, assigns, heirs, executors, administrators, trustees in bankruptcy and legal representatives of the undersigned and shall not be affected by, and shall survive, the death or incapacity of the undersigned.

Name:

Amount Tendered (if less than all):

Address:

Name of Tendering Institution:

Account Number:

Transaction Code Number:

By crediting the Old Notes to the Exchange Agent’s account at DTC using ATOP and by complying with applicable ATOP procedures with respect to the Exchange Offer, the participant in DTC confirms on behalf of itself and the beneficial owners of such Old Notes all provisions of this Letter of Transmittal (including all representations and warranties) applicable to it and such beneficial owner as fully as if it had completed the information required herein and executed and transmitted this Letter of Transmittal to the Exchange Agent.

INSTRUCTIONS FORMING PART OF

THE TERMS AND CONDITIONS OF THE EXCHANGE OFFER

1. Book-Entry Confirmations

Any confirmation of a book-entry transfer to the Exchange Agent’s account at DTC of the Old Notes tendered by book-entry transfer, as well as an agent’s message, and any other documents required by this Letter of Transmittal, must be received by the Exchange Agent at its address set forth on the cover page of this Letter of Transmittal prior to the Expiration Date.

2. Validity of Tenders

The Issuer will determine in their sole discretion all questions as to the validity, form, eligibility, time of receipt, acceptance of tendered Old Notes and withdrawal of tendered Old Notes. The Issuer’s determination will be final and binding. The Issuer reserves the absolute right to reject any Old Notes not properly tendered or any acceptance of the Old Notes that would, in the opinion of its counsel, be unlawful. The Issuer also reserves the right to waive any defect, irregularities or conditions of tender as to particular Old Notes. The Issuer’s interpretation of the terms and conditions of the Exchange Offer, including the instructions in this Letter of Transmittal, will be final and binding on all parties. Unless waived, all defects or irregularities in connection with tenders of the Old Notes must be cured within such time as the Issuer shall determine. Although the Issuer intends to notify holders of defects or irregularities with respect to tenders of the Old Notes, none of the Issuer, the Exchange Agent, the Trustee and any other person will incur any liability for failure to give such notification. Tenders of the Old Notes will not be deemed made until such defects or irregularities have been cured or waived. Any Old Notes received by the Exchange Agent that are not properly tendered and as to which the defects or irregularities have not been cured or waived will be returned to the tendering holder through the facilities of DTC as soon as practicable after the Expiration Date.

3. Waiver of Conditions

The Issuer reserves the absolute right to waive, in whole or part, at any time or from time to time, any of the conditions to the Exchange Offer set forth in the Prospectus or in this Letter of Transmittal.

4. No Conditional Tender

No alternative, conditional, irregular or contingent tender of the Old Notes will be accepted.

5. Request for Assistance

Requests for assistance regarding the Prospectus or this Letter of Transmittal may be directed to the Exchange Agent at the address, telephone numbers or fax number set forth on the cover page of this Letter of Transmittal. Holders may also contact their commercial bank, broker, dealer, trust company or other nominee for assistance concerning the Exchange Offer.

6. Withdrawal

Tenders of the Old Notes may be withdrawn at any time prior to the Expiration Date. For a withdrawal to be effective you must comply with the appropriate ATOP procedures. Any notice of withdrawal must specify the name and number of the account at DTC to be credited with withdrawn Old Notes and otherwise comply with the ATOP procedures. For more information, see the section of the Prospectus entitled “Description of the Exchange Offer—Withdrawal of Tenders.”

7. Transfer Taxes

Holders who tender their Old Notes for exchange will not be obligated to pay any transfer taxes in connection with that tender or exchange, except that holders who instruct the Issuer to register the New Notes in

the name of, or request that the Old Notes not tendered or not accepted in the Exchange Offer be returned to, a person other than the registered tendering holder will be responsible for the payment of any applicable transfer tax on those Old Notes.

IMPORTANT: BY USING THE ATOP PROCEDURES TO TENDER THE OLD NOTES, YOU WILL NOT BE REQUIRED TO DELIVER THIS LETTER OF TRANSMITTAL TO THE EXCHANGE AGENT. HOWEVER, YOU WILL BE BOUND BY ITS TERMS, AND YOU WILL BE DEEMED TO HAVE MADE THE ACKNOWLEDGMENTS AND THE REPRESENTATIONS AND WARRANTIES IT CONTAINS, JUST AS IF YOU HAD SIGNED IT.