Starboard Value SC 13D/A QUANTUM / Starboard Value ownership change

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

(Rule 13d-101)

INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT

TO § 240.13d-1(a) AND AMENDMENTS THERETO FILED PURSUANT TO

§ 240.13d-2(a)

(Amendment No. 2)1

Quantum Corporation

(Name of Issuer)

Common Stock, par value $0.01 per share

(Title of Class of Securities)

747906204

(CUSIP Number)

JEFFREY C. SMITH

STARBOARD VALUE LP

830 Third Avenue, 3rd Floor

New York, New York 10022

(212) 845-7977

STEVE WOLOSKY, ESQ.

OLSHAN FROME WOLOSKY LLP

Park Avenue Tower

65 East 55th Street

New York, New York 10022

(212) 451-2300

(Name, Address and Telephone Number of Person

Authorized to Receive Notices and Communications)

May 13, 2013

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box ¨.

Note:  Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits.  See § 240.13d-7 for other parties to whom copies are to be sent.

_______________

1              The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

CUSIP NO. 747906204

1	NAME OF REPORTING PERSON STARBOARD VALUE AND OPPORTUNITY MASTER FUND LTD
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) o   (b) o
3	SEC USE ONLY
4	SOURCE OF FUNDS WC
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION CAYMAN ISLANDS
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	7	SOLE VOTING POWER 26,128,823*
	8	SHARED VOTING POWER - 0 -
	9	SOLE DISPOSITIVE POWER 26,128,823*
	10	SHARED DISPOSITIVE POWER - 0 -
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 26,128,823*
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 10.3%
14	TYPE OF REPORTING PERSON CO

* Includes Shares underlying certain convertible senior subordinated notes.

2

CUSIP NO. 747906204

1	NAME OF REPORTING PERSON STARBOARD VALUE AND OPPORTUNITY S LLC
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) o   (b) o
3	SEC USE ONLY
4	SOURCE OF FUNDS WC
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	7	SOLE VOTING POWER 5,862,924*
	8	SHARED VOTING POWER - 0 -
	9	SOLE DISPOSITIVE POWER 5,862,924*
	10	SHARED DISPOSITIVE POWER - 0 -
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 5,862,924*
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 2.4%
14	TYPE OF REPORTING PERSON OO

* Includes Shares underlying certain convertible senior subordinated notes.

3

CUSIP NO. 747906204

1	NAME OF REPORTING PERSON STARBOARD VALUE AND OPPORTUNITY C LP
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) o   (b) o
3	SEC USE ONLY
4	SOURCE OF FUNDS WC
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	7	SOLE VOTING POWER 3,008,940*
	8	SHARED VOTING POWER - 0 -
	9	SOLE DISPOSITIVE POWER 3,008,940*
	10	SHARED DISPOSITIVE POWER - 0 -
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 3,008,940*
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 1.2%
14	TYPE OF REPORTING PERSON PN

* Includes Shares underlying certain convertible senior subordinated notes.

4

CUSIP NO. 747906204

1	NAME OF REPORTING PERSON STARBOARD VALUE R LP
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) o   (b) o
3	SEC USE ONLY
4	SOURCE OF FUNDS OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	7	SOLE VOTING POWER 3,008,940*
	8	SHARED VOTING POWER - 0 -
	9	SOLE DISPOSITIVE POWER 3,008,940*
	10	SHARED DISPOSITIVE POWER - 0 -
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 3,008,940*
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 1.2%
14	TYPE OF REPORTING PERSON PN

* Includes Shares underlying certain convertible senior subordinated notes.

5

CUSIP NO. 747906204

1	NAME OF REPORTING PERSON STARBOARD VALUE R GP LLC
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) o   (b) o
3	SEC USE ONLY
4	SOURCE OF FUNDS OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	7	SOLE VOTING POWER 3,008,940*
	8	SHARED VOTING POWER - 0 -
	9	SOLE DISPOSITIVE POWER 3,008,940*
	10	SHARED DISPOSITIVE POWER - 0 -
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 3,008,940*
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 1.2%
14	TYPE OF REPORTING PERSON OO

* Includes Shares underlying certain convertible senior subordinated notes.

6

CUSIP NO. 747906204

1	NAME OF REPORTING PERSON STARBOARD VALUE LP
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) o   (b) o
3	SEC USE ONLY
4	SOURCE OF FUNDS OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	7	SOLE VOTING POWER 44,243,875*
	8	SHARED VOTING POWER - 0 -
	9	SOLE DISPOSITIVE POWER 44,243,875*
	10	SHARED DISPOSITIVE POWER - 0 -
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 44,243,875*
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 17.0%
14	TYPE OF REPORTING PERSON PN

* Includes Shares underlying certain convertible senior subordinated notes.

7

CUSIP NO. 747906204

1	NAME OF REPORTING PERSON STARBOARD VALUE GP LLC
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) o   (b) o
3	SEC USE ONLY
4	SOURCE OF FUNDS OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	7	SOLE VOTING POWER 44,243,875*
	8	SHARED VOTING POWER - 0 -
	9	SOLE DISPOSITIVE POWER 44,243,875*
	10	SHARED DISPOSITIVE POWER - 0 -
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 44,243,875*
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 17.0%
14	TYPE OF REPORTING PERSON OO

* Includes Shares underlying certain convertible senior subordinated notes.

8

CUSIP NO. 747906204

1	NAME OF REPORTING PERSON STARBOARD PRINCIPAL CO LP
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) o   (b) o
3	SEC USE ONLY
4	SOURCE OF FUNDS OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	7	SOLE VOTING POWER 44,243,875*
	8	SHARED VOTING POWER - 0 -
	9	SOLE DISPOSITIVE POWER 44,243,875*
	10	SHARED DISPOSITIVE POWER - 0 -
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 44,243,875*
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 17.0%
14	TYPE OF REPORTING PERSON PN

* Includes Shares underlying certain convertible senior subordinated notes.

9

CUSIP NO. 747906204

1	NAME OF REPORTING PERSON STARBOARD PRINCIPAL CO GP LLC
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) o   (b) o
3	SEC USE ONLY
4	SOURCE OF FUNDS OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION DELAWARE
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	7	SOLE VOTING POWER 44,243,875*
	8	SHARED VOTING POWER - 0 -
	9	SOLE DISPOSITIVE POWER 44,243,875*
	10	SHARED DISPOSITIVE POWER - 0 -
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 44,243,875*
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 17.0%
14	TYPE OF REPORTING PERSON OO

* Includes Shares underlying certain convertible senior subordinated notes.

10

CUSIP NO. 747906204

1	NAME OF REPORTING PERSON JEFFREY C. SMITH
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) o   (b) o
3	SEC USE ONLY
4	SOURCE OF FUNDS OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION USA
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	7	SOLE VOTING POWER - 0 -
	8	SHARED VOTING POWER 44,243,875*
	9	SOLE DISPOSITIVE POWER - 0 -
	10	SHARED DISPOSITIVE POWER 44,243,875*
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 44,243,875*
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 17.0%
14	TYPE OF REPORTING PERSON IN

* Includes Shares underlying certain convertible senior subordinated notes.

11

CUSIP NO. 747906204

1	NAME OF REPORTING PERSON MARK R. MITCHELL
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) o   (b) o
3	SEC USE ONLY
4	SOURCE OF FUNDS OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION USA
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	7	SOLE VOTING POWER - 0 -
	8	SHARED VOTING POWER 44,243,875*
	9	SOLE DISPOSITIVE POWER - 0 -
	10	SHARED DISPOSITIVE POWER 44,243,875*
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 44,243,875*
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 17.0%
14	TYPE OF REPORTING PERSON IN

* Includes Shares underlying certain convertible senior subordinated notes.

12

CUSIP NO. 747906204

1	NAME OF REPORTING PERSON PETER A. FELD
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) o   (b) o
3	SEC USE ONLY
4	SOURCE OF FUNDS OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)		¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION USA
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	7	SOLE VOTING POWER - 0 -
	8	SHARED VOTING POWER 44,243,875*
	9	SOLE DISPOSITIVE POWER - 0 -
	10	SHARED DISPOSITIVE POWER 44,243,875*
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 44,243,875*
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 17.0%
14	TYPE OF REPORTING PERSON IN

* Includes Shares underlying certain convertible senior subordinated notes.

13

CUSIP NO. 747906204

The following constitutes Amendment No. 2 to the Schedule 13D filed by the undersigned (“Amendment No. 2”).  This Amendment No. 2 amends the Schedule 13D as specifically set forth herein.

Item 2. Identity and Background.

Item 2 is hereby amended and restated as follows:

(a)           This statement is filed by:

(i) Starboard Value and Opportunity Master Fund Ltd, a Cayman Islands exempted company (“Starboard V&O Fund”), with respect to the Shares directly and beneficially owned by it;

(ii) Starboard Value and Opportunity S LLC, a Delaware limited liability company (“Starboard LLC”), with respect to the Shares directly and beneficially owned by it;

(iii) Starboard Value and Opportunity C LP, a Delaware limited partnership (“Starboard C LP”), with respect to the Shares directly and beneficially owned by it;

(iv) Starboard Value LP (“Starboard Value LP”), as the investment manager of Starboard V&O Fund, Starboard C LP and of a certain managed account (the “Starboard Value LP Account”) and the manager of Starboard LLC;

(v) Starboard Value GP LLC (“Starboard Value GP”), as the general partner of Starboard Value LP;

(vi) Starboard Principal Co LP (“Principal Co”), as a member of Starboard Value GP;

(vii) Starboard Principal Co GP LLC (“Principal GP”), as the general partner of Principal Co;

(viii) Starboard Value R LP (“Starboard R LP”), as the general partner of Starboard C LP;

(ix) Starboard Value R GP LLC (“Starboard R GP”), as the general partner of Starboard R LP;

(x) Jeffrey C. Smith, as a member of Principal GP and as a member of each of the Management Committee of Starboard Value GP and the Management Committee of Principal GP;

(xi) Mark R. Mitchell, as a member of Principal GP and as a member of each of the Management Committee of Starboard Value GP and the Management Committee of Principal GP; and

(xii) Peter A. Feld, as a member of Principal GP and as a member of each of the Management Committee of Starboard Value GP and the Management Committee of Principal GP.

14

CUSIP NO. 747906204

Each of the foregoing is referred to as a “Reporting Person” and collectively as the “Reporting Persons.”  Each of the Reporting Persons is party to that certain Joint Filing Agreement, as further described in Item 6.  Accordingly, the Reporting Persons are hereby filing a joint Schedule 13D.

(b)           The address of the principal office of each of Starboard LLC, Starboard C LP, Starboard Value LP, Starboard Value GP, Principal Co, Principal GP, Starboard R LP, Starboard R GP, and Messrs. Smith, Mitchell and Feld is 830 Third Avenue, 3rd Floor, New York, New York 10022.  The address of the principal office of Starboard V&O Fund is 89 Nexus Way, Camana Bay, PO Box 31106, Grand Cayman KY1-1205, Cayman Islands.  The officers and directors of Starboard V&O Fund and their principal occupations and business addresses are set forth on Schedule A to the Schedule 13D and are incorporated by reference in this Item 2.

(c)           The principal business of Starboard V&O Fund is serving as a private investment fund.  Starboard V&O Fund has been formed for the purpose of making equity investments and, on occasion, taking an active role in the management of portfolio companies in order to enhance shareholder value.  Starboard LLC and Starboard C LP have been formed for the purpose of investing in securities and engaging in all related activities and transactions.  Starboard Value LP provides investment advisory and management services and acts as the investment manager of Starboard V&O Fund, Starboard C LP and the Starboard Value LP Account and the manager of Starboard LLC.  The principal business of Starboard Value GP is providing a full range of investment advisory, pension advisory and management services and serving as the general partner of Starboard Value LP.  The principal business of Principal Co is providing investment advisory and management services.  Principal Co is a member of Starboard Value GP.  Principal GP serves as the general partner of Principal Co.  Starboard R LP serves as the general partner of Starboard C LP. Starboard R GP serves as the general partner of Starboard R LP.  Messrs. Smith, Mitchell and Feld serve as members of Principal GP and the members of each of the Management Committee of Starboard Value GP and the Management Committee of Principal GP.

(d)           No Reporting Person, nor any person listed on Schedule A to the Schedule 13D, annexed hereto, has, during the last five years, been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors).

(e)           No Reporting Person, nor any person listed on Schedule A to the Schedule 13D, has, during the last five years, been party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.

(f)           Messrs. Smith, Mitchell and Feld are citizens of the United States of America.  The citizenship of the persons listed on Schedule A to the Schedule 13D is set forth therein.

Item 3. Source and Amount of Funds or Other Consideration.

Item 3 is hereby amended and restated as follows:

The Shares purchased by each of Starboard V&O Fund, Starboard LLC and Starboard C LP and held in the Starboard Value LP Account were purchased with working capital (which may, at any given time, include margin loans made by brokerage firms in the ordinary course of business) in open market purchases, except as otherwise noted, as set forth in Schedule A, which is incorporated by reference herein.  The aggregate purchase price of the 26,128,823 Shares beneficially owned by Starboard V&O Fund is approximately $38,354,507, excluding brokerage commissions.  Such aggregate purchase price includes $18,960,000, which is the purchase price of $18,960,000 principal amount of Notes (as defined in the Schedule 13D) convertible into 11,511,839 Shares.  The aggregate purchase price of the 5,862,924 Shares beneficially owned by Starboard LLC is approximately $8,606,755, excluding brokerage commissions.  Such aggregate purchase price includes $4,260,000, which is the purchase price of $4,260,000 principal amount of Notes convertible into 2,586,521 Shares.  The aggregate purchase price of the 3,008,940 Shares beneficially owned by Starboard C LP is approximately $3,867,186, excluding brokerage commissions.  Such aggregate purchase price includes $565,788, which is the purchase price of $550,000 principal amount of the Notes convertible into 333,940 Shares.  The aggregate purchase price of the 9,243,188 Shares held in the Starboard Value LP Account is approximately $13,579,188, excluding brokerage commissions.  Such aggregate purchase price includes $6,780,000, which is the purchase price of $6,780,000 principal amount of Notes convertible into 4,116,575 Shares.

15

CUSIP NO. 747906204

Item 4. Purpose of Transaction.

Item 4 is hereby amended to add the following:

On May 13, 2013, Starboard (as defined in the Settlement Agreement) and the Issuer entered into a settlement agreement (the “Settlement Agreement”). The following description of the Settlement Agreement is qualified in its entirety by reference to the Settlement Agreement, which is attached as Exhibit 99.1 hereto and is incorporated herein by reference.

Pursuant to the terms of the Settlement Agreement, the Issuer agreed, among other things: (i) to immediately increase the size of the Board of Directors of the Issuer (the “Board”) from eight (8) to nine (9) members; (ii) to appoint Jeffrey Smith to the Board immediately; (iii) to nominate and solicit proxies for the election of Louis DiNardo and Philip Black (together with Messrs. DiNardo and Smith, the “Starboard Nominees”) to the Board at the 2013 annual meeting of stockholders of the Issuer (the “2013 Annual Meeting”); (iv) in the interim, to appoint Messrs. DiNardo and Black as observers to the Board, subject to attorney-client privilege and their execution of a confidentiality agreement; (v) promptly following the date of the Settlement Agreement, but no later than 30 days from such date, to appoint Mr. Smith to the Leadership and Compensation Committee of the Board; and (vi) promptly following the conclusion of the 2013 Annual Meeting, but no later than 30 days thereafter, to appoint Mr. DiNardo as chairman of the Governance Committee of the Board and appoint Mr. Black to the Audit Committee of the Board.  If any Starboard Nominee is unable to serve as a director, resigns or is removed as a director prior to the 2014 annual meeting of stockholders of the Issuer (the “2014 Annual Meeting”) and at such time Starboard beneficially owns in the aggregate, excluding Shares underlying the Notes, at least three percent (3.0%) of the Issuer’s then outstanding Shares, then Starboard can recommend substitute person(s) who meet certain independence and experience criteriafor approval by the Corporate Governance and Nominating Committee of the Board and appointment by the Board within five (5) business days after such committee’s approval.

The Issuer further agreed not to increase the size of the Board to more than nine (9) directors during the Standstill Period (as defined in the Settlement Agreement) and to use its reasonable best efforts to hold the 2013 Annual Meeting no later than September 15, 2013.

Pursuant to the terms of the Settlement Agreement, Starboard agreed, among other things: (i) not to nominate any person for election at the 2013 Annual Meeting; (ii) not to submit any proposal for consideration at, or bring any other business before, the 2013 Annual Meeting, directly or indirectly; (iii) not to initiate, encourage or participate in any “withhold” or similar campaign with respect to the 2013 Annual Meeting, directly or indirectly; (iv) to appear in person or by proxy at the 2013 Annual Meeting and vote all Shares beneficially owned by it in favor of the election of each of the Issuer’s nominees for election to the Board and in accordance with the Board’s recommendation with respect to the Issuer’s “say-on-pay” proposal, unless Institutional Shareholder Services Inc. recommends otherwise; and (v) to obtain an irrevocable resignation letter from Mr. Smith pursuant to which he will resign from the Board and all applicable committees thereof if at any time during the Standstill Period Starboard’s aggregate beneficial ownership of the Shares, excluding Shares underlying the Notes, decreases to less than three percent (3.0%) of the Issuer’s then outstanding Shares.

16

CUSIP NO. 747906204

In addition, Starboard agreed, from the date of the Settlement Agreement through the earlier of (a) fifteen (15) business days prior to the deadline for the submission of stockholder nominations for the  2014 Annual Meeting and (b) one-hundred (100) days prior to the first anniversary of the 2013 Annual Meeting, not to, directly or indirectly, in any manner: (i) engage in any solicitation of proxies or consents or become a “participant” in a “solicitation” as such terms are defined in Regulation 14A under the Securities Exchange Act of 1934, as amended (the “Exchange Act”) of proxies or consents; (ii) form, join or in any way participate in any “group” (within the meaning of Section 13(d)(3) of the Exchange Act) with respect to the Shares;  (iii) deposit any Shares in any voting trust or subject any Shares to any arrangement or agreement with respect to the voting of any Shares, other than any such voting trust, arrangement or agreement solely among the members of Starboard; (iv) seek or encourage any person to submit nominations in furtherance of a “contested solicitation,” or take other action,  for the election or removal of directors with respect to the Issuer; (v) (A) make any proposal for consideration by stockholders at any annual or special meeting of stockholders of the Issuer, (B) make any offer or proposal with respect to a merger, acquisition, recapitalization, restructuring, disposition or other business combination involving the Issuer, or encourage, initiate or support any other third party in any such related activity or (C) make any public communication in opposition to any Issuer acquisition or disposition activity approved by the Board; (vi) seek, alone or in concert with others, representation on the Board; (vii) seek to advise, encourage, support or influence any person with respect to the voting or disposition of any securities of the Issuer at any annual or special meeting of stockholders; or (viii) make any request or submit any proposal to amend the terms of the Settlement Agreement other than through non-public communications with the Issuer that would not be reasonably determined to trigger public disclosure obligations for Starboard or the Issuer.

On May 14, 2013, the Issuer and Starboard jointly issued a mutually agreeable press release to announce they have reached a Settlement Agreement.

Item 5. Interest in Securities of the Issuer.

Items 5(a)-(c) are hereby amended and restated to read as follows:

The aggregate percentage of Shares reported owned by each person named herein is calculated using as the numerator the respective Shares held by each Reporting Person, including Shares issuable upon conversion of the Notes, and as the denominator 240,962,472 Shares outstanding, as of February 1, 2013, which is the total number of Shares outstanding as reported in the Issuer’s Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission on February 8, 2013, plus the number of Shares issuable upon conversion of the Notes held by such Reporting Person.

A. Starboard V&O Fund

(a) As of the close of business on May 14, 2013, Starboard V&O Fund beneficially owned 26,128,823Shares, including 11,511,839 Shares underlying the Notes.

Percentage: Approximately 10.3%

17

CUSIP NO. 747906204

(b) 1. Sole power to vote or direct vote: 26,128,823

2. Shared power to vote or direct vote: 0

3. Sole power to dispose or direct the disposition: 26,128,823

4. Shared power to dispose or direct the disposition: 0

(c) Starboard V&O Fund has not entered into any transactions in the Shares during the past sixty days.

B. Starboard LLC

(a) As of the close of business on May 14, 2013, Starboard LLC beneficially owned 5,862,924Shares, including 2,586,521 Shares underlying the Notes.

Percentage: Approximately 2.4%

(b) 1. Sole power to vote or direct vote: 5,862,924

2. Shared power to vote or direct vote: 0

3. Sole power to dispose or direct the disposition: 5,862,924

4. Shared power to dispose or direct the disposition: 0

(c) Starboard LLC has not entered into any transactions in the Shares during the past sixty days.

C. Starboard C LP

(a) As of the close of business on May 14, 2013, Starboard C LP beneficially owned 3,008,940 Shares, including 333,940 Shares underlying the Notes.

Percentage: Approximately 1.2%

(b) 1. Sole power to vote or direct vote: 3,008,940

2. Shared power to vote or direct vote:  0

3. Sole power to dispose or direct the disposition: 3,008,940

4. Shared power to dispose or direct the disposition: 0

(c) The transactions in the Shares by Starboard C LP during the past sixty days are set forth in Schedule A and are incorporated herein by reference.

D. Starboard R LP

(a) Starboard R LP, as the general partner of Starboard C LP, may be deemed the beneficial owner of the 3,008,940 shares owned by Starboard C LP.

Percentage: Approximately 1.2%

(b) 1. Sole power to vote or direct vote: 3,008,940

2. Shared power to vote or direct vote: 0

3. Sole power to dispose or direct the disposition: 3,008,940

4. Shared power to dispose or direct the disposition: 0

(c) Starboard R LP has not entered into any transactions in the Shares during the past sixty days.  The transactions in the Shares on behalf of Starboard C LP during the past sixty days are set forth in Schedule A and are incorporated herein by reference.

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E.           Starboard R GP

(a) Starboard R GP, as the general partner of Starboard R LP, may be deemed the beneficial owner of the 3,008,940 shares owned by Starboard C LP.

Percentage: Approximately 1.2%

(b) 1. Sole power to vote or direct vote: 3,008,940

2. Shared power to vote or direct vote: 0

3. Sole power to dispose or direct the disposition: 3,008,940

4. Shared power to dispose or direct the disposition: 0

(c) Starboard R GP has not entered into any transactions in the Shares during the past sixty days.  The transactions in the Shares on behalf of Starboard C LP during the past sixty days are set forth in Schedule A and are incorporated herein by reference.

F. Starboard Value LP

(a) As of the close of business on May 14, 2013, 9,243,188 Shares were held in the Starboard Value LP Account, including 4,116,575 Shares underlying the Notes.  Starboard Value LP, as the investment manager of Starboard V&O Fund, Starboard C LP and the Starboard Value Account and the manager of Starboard LLC, may be deemed the beneficial owner of the (i) 26,128,823Shares owned by Starboard V&O Fund, (ii) 5,862,924 Shares owned by Starboard LLC, (iii) 3,008,940 Shares owned by Starboard C LP and (iv) 9,243,188 Shares held in the Starboard Value LP Account.

Percentage: Approximately 17.0%

(b) 1. Sole power to vote or direct vote: 44,243,875

2. Shared power to vote or direct vote: 0

3. Sole power to dispose or direct the disposition: 44,243,875

4. Shared power to dispose or direct the disposition: 0

(c) Starboard Value LP has not entered into any transactions in the Shares during the past sixty days. The transactions in the Shares on behalf of Starboard C LP during the past sixty days are set forth in Schedule A and are incorporated herein by reference.

G. Starboard Value GP

(a) Starboard Value GP, as the general partner of Starboard Value LP, may be deemed the beneficial owner of the (i) 26,128,823Shares owned by Starboard V&O Fund, (ii) 5,862,924 Shares owned by Starboard LLC, (iii) 3,008,940 Shares owned by Starboard C LP and (iv) 9,243,188 Shares held in the Starboard Value LP Account.

Percentage: Approximately 17.0%

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(b) 1. Sole power to vote or direct vote: 44,243,875

2. Shared power to vote or direct vote: 0

3. Sole power to dispose or direct the disposition: 44,243,875

4. Shared power to dispose or direct the disposition: 0

(c) Starboard Value GP has not entered into any transactions in the Shares during the past sixty days.  The transactions in the Shares on behalf of Starboard C LP during the past sixty days are set forth in Schedule A and are incorporated herein by reference.

H. Principal Co

(a) Principal Co, as a member of Starboard Value GP, may be deemed the beneficial owner of the (i) 26,128,823 Shares owned by Starboard V&O Fund, (ii) 5,862,924 Shares owned by Starboard LLC, (iii) 3,008,940 Shares owned by Starboard C LP and (iv) 9,243,188 Shares held in the Starboard Value LP Account.

Percentage: Approximately 17.0%

(b) 1. Sole power to vote or direct vote: 44,243,875

2. Shared power to vote or direct vote: 0

3. Sole power to dispose or direct the disposition: 44,243,875

4. Shared power to dispose or direct the disposition: 0

(c) Principal Co has not entered into any transactions in the Shares during the past sixty days.  The transactions in the Shares on behalf of Starboard C LP during the past sixty days are set forth in Schedule A and are incorporated herein by reference.

I. Principal GP

(a) Principal GP, as the general partner of Principal Co, may be deemed the beneficial owner of the (i) 26,128,823Shares owned by Starboard V&O Fund, (ii) 5,862,924 Shares owned by Starboard LLC, (iii) 3,008,940 Shares owned by Starboard C LP and (iv) 9,243,188 Shares held in the Starboard Value LP Account.

Percentage: Approximately 17.0%

(b) 1. Sole power to vote or direct vote: 44,243,875

2. Shared power to vote or direct vote: 0

3. Sole power to dispose or direct the disposition: 44,243,875

4. Shared power to dispose or direct the disposition: 0

(c) Principal GP has not entered into any transactions in the Shares during the past sixty days.  The transactions in the Shares on behalf of Starboard C LP during the past sixty days are set forth in Schedule A and are incorporated herein by reference.

J. Messrs. Smith, Mitchell and Feld

(a) Each of Messrs. Smith, Mitchell and Feld, as a member of Principal GP and as a member of each of the Management Committee of Starboard Value GP and the Management Committee of Principal GP, may be deemed the beneficial owner of the (i) 26,128,823Shares owned by Starboard V&O Fund, (ii) 5,862,924 Shares owned by Starboard LLC, (iii) 3,008,940 Shares owned by Starboard C LP and (iv) 9,243,188 Shares held in the Starboard Value LP Account.

Percentage: Approximately 17.0%

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(b) 1. Sole power to vote or direct vote: 0

2. Shared power to vote or direct vote: 44,243,875

3. Sole power to dispose or direct the disposition: 0

4. Shared power to dispose or direct the disposition: 44,243,875

(c) None of Messrs. Smith, Mitchell or Feld has entered into any transactions in the Shares during the past sixty days.  The transactions in the Shares on behalf of Starboard C LP during the past sixty days are set forth in Schedule A and are incorporated herein by reference.

Item 6. Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer.

Item 6 is amended to add the following:

On May 13, 2013, Starboard and the Issuer entered into a Settlement Agreement defined and described in Item 4 above and attached as Exhibit 99.1 hereto.

On May 14, 2013, Starboard R LP and Starboard R GP entered into a joinder agreement to that certain Joint Filing Agreement dated as of November 1, 2012 by and among Starboard V&O Fund, Starboard LLC, Starboard Value LP, Starboard Value GP, Principal Co, Principal GP and Messrs. Smith, Mitchell and Feld, pursuant to which each of Starboard R LP and Starboard R GP agreed to be bound by the terms and conditions set forth therein, including, the joint filing on behalf of each of them of statements on Schedule 13D, and any amendments thereto, with respect to the securities of the Issuer.  A copy of the joinder agreement is attached hereto as Exhibit 99.2 and is incorporated herein by reference.  A copy of the Joint Filing Agreement was filed as Exhibit 99.1 to the Schedule 13D.

Item 7. Material to be Filed as Exhibits.

Item 7 is amended to add the following exhibits:

99.1 Settlement Agreement, dated as of May 13, 2013, by and among Starboard and Quantum Corporation.

99.2 Joinder Agreement dated May 14, 2013 to the Joint Filing Agreement.

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SIGNATURES

After reasonable inquiry and to the best of his knowledge and belief, each of the undersigned certifies that the information set forth in this statement is true, complete and correct.

Dated:  May 15, 2013

STARBOARD VALUE AND OPPORTUNITY MASTER FUND LTD By: Starboard Value LP,        its investment manager   STARBOARD VALUE AND OPPORTUNITY S LLC By: Starboard Value LP,        its manager   STARBOARD VALUE AND OPPORTUNITY C LP By: Starboard Value R LP,        its general partner   STARBOARD VALUE R LP By: Starboard Value R GP LLC,        its general partner   STARBOARD VALUE LP By: Starboard Value GP LLC,        its general partner   STARBOARD VALUE GP LLC By: Starboard Principal Co LP,        its member   STARBOARD PRINCIPAL CO LP By: Starboard Principal Co GP LLC,        its general partner   STARBOARD PRINCIPAL CO GP LLC   STARBOARD VALUE R GP LLC

By:	/s/ Jeffrey C. Smith
	Name:	Jeffrey C. Smith
	Title:	Authorized Signatory

/s/ Jeffrey C. Smith

JEFFREY C. SMITH

Individually and as attorney-in-fact for Mark R. Mitchell and Peter A. Feld

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CUSIP NO. 747906204

SCHEDULE A

Transactions in the Shares During the Past Sixty Days

Shares of Common Stock Purchased Price Per Share($) Date of Purchase

STARBOARD VALUE AND OPPORTUNITY C LP

500,000	1.2500	04/01/2013
500,000	1.2500	04/02/2013
125,000	1.2337	04/02/2013
300,000	1.2322	04/03/2013
250,000	1.2301	04/04/2013