UNITED STATES
                  SECURITIES AND EXCHANGE COMMISSION
                        Washington, D.C. 20549


                             SCHEDULE 13G

               Under the Securities Exchange Act of 1934


                          (Amendment No. 2)*


                           Quantum Corporation
                             (Name of Issuer)

                               Common Stock
                      (Title of Class of Securities)

                                747906204
                              (CUSIP Number)

                            December 30, 2011
         (Date of Event Which Requires Filing of this Statement)


Check the appropriate box to designate the rule pursuant to which this
Schedule is filed:
[X] Rule 13d-1(b)
[ ] Rule 13d-1(c)
[ ] Rule 13d-1(d)


*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 the disclosures provided in a prior cover page.

The information required in 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: 747906204                                                Page 1 of 5



 1   NAMES OF REPORTING PERSONS
     I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)
     Capital Research Global Investors **


 2   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE
     INSTRUCTIONS)                                                 (a)

                                                                    (b)
 3   SEC USE ONLY


 4   CITIZENSHIP OR PLACE OF ORGANIZATION

     Delaware

             5   SOLE VOTING POWER

                  16,663,897


             6   SHARED VOTING POWER
 NUMBER OF
   SHARES         NONE
BENEFICIALL
 Y OWNED BY
             7   SOLE DISPOSITIVE POWER
    EACH
 REPORTING        18,279,499
   PERSON
   WITH:
             8   SHARED DISPOSITIVE POWER

                  NONE

 9   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

     18,279,499          Beneficial ownership disclaimed pursuant to Rule
     13d-4


 10  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES
     (SEE INSTRUCTIONS)


 11  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

     7.8%

 12  TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

     IA

** A division of Capital Research and Management Company (CRMC)






CUSIP: 747906204                                                Page 2 of 5


                  SECURITIES AND EXCHANGE COMMISSION
                         Washington, DC 20549

                             Schedule 13G
               Under the Securities Exchange Act of 1934

Amendment No. 2

Item 1(a)     Name of Issuer:
       Quantum Corporation

Item 1(b)     Address of Issuer's Principal Executive Offices:
       1650 Technology Drive, Suite 800
       San Jose, California 95110

Item 2(a)     Name of Person(s) Filing:
       Capital Research Global Investors

Item 2(b)     Address of Principal Business Office or, if none,
       Residence:
       333 South Hope Street
       Los Angeles, CA 90071

Item 2(c)     Citizenship:   N/A

Item 2(d)     Title of Class of Securities:
       Common Stock

Item 2(e)     CUSIP Number:
       747906204

Item 3     If this statement is filed pursuant to sections 240.13d-1(b)
       or 240.13d-2(b) or (c), check whether the person filing is a:
       (e)      [X]     An investment adviser in accordance with
            section 240.13d-1(b)(1)(ii)(E).

Item 4     Ownership

       Provide the following information regarding the aggregate
       number and percentage of the class of securities of the issuer
       identified in Item 1.


       (a)    Amount beneficially owned:
       (b)    Percent of class:
       (c)    Number of shares as to which the person has:
       (i)    Sole power to vote or to direct the vote:
       (ii)   Shared power to vote or to direct the vote:
       (iii)  Sole power to dispose or to direct the disposition of:
       (iv)   Shared power to dispose or to direct the disposition of:

       See page 2

       Capital Research Global Investors is deemed to be the
       beneficial owner of 18,279,499 shares or 7.8% of the
       235,315,602 shares believed to be outstanding as a result of
       CRMC acting as investment adviser to various investment
       companies registered under Section 8 of the Investment Company
       Act of 1940.

CUSIP: 747906204                                                Page 3 of 5
 

       Shares reported by Capital Research Global Investors include
       1,615,602 shares resulting from the assumed conversion of
       $7,000,000 of the principal amount of 3.50% convertible
       subordinated notes due November 15, 2015.

Item 5     Ownership of Five Percent or Less of a Class.  If this
       statement is being filed to report the fact that as of the date
       hereof the reporting person has ceased to be the beneficial
       owner of more than five percent of the class of securities,
       check the following: [ ]

Item 6     Ownership of More than Five Percent on Behalf of Another
       Person: One or more clients of Capital Research Global
       Investors have the right to receive or the power to direct the
       receipt of dividends from, or the proceeds from the sale of,
       the Common Stock of Quantum Corporation.  Capital Research
       Global Investors holds more than five percent of the
       outstanding Common Stock of Quantum Corporation as of December
       30, 2011 on behalf of each of the following client(s):

       SMALLCAP World Fund, Inc.

Item 7     Identification and Classification of the Subsidiary Which
       Acquired the Security Being Reported on By the Parent Holding
       Company or Control Person: N/A

Item 8     Identification and Classification of Members of the Group:
       N/A

Item 9     Notice of Dissolution of Group:  N/A

Item 10     Certification

       By signing below, I certify that, to the best of my knowledge
       and belief, the securities referred to above were acquired and
       are held in the ordinary course of business and were not
       acquired and are not held for the purpose of or with the effect
       of changing or influencing the control of the issuer of the
       securities and were not acquired and are not held in connection
       with or as a participant in any transaction having that purpose
       or effect.

     Signature

       After reasonable inquiry and to the best of my knowledge and
       belief, I certify that the information set forth in this
       statement is true, complete and correct.

        Date:          February 1, 2012

        Signature:     Timothy D. Armour***
        Name/Title:    Timothy D. Armour - Senior Vice President
                       Capital Research Global Investors







CUSIP: 747906204                                                Page 4 of 5
 

        ***By  /s/ James P. Ryan
               James P. Ryan
               Attorney-in-fact

          Signed pursuant to a Power of Attorney dated December 29,
          2010 included as an Exhibit to Schedule 13G filed with the
          Securities and Exchange Commission by Capital Research Global
          Investors on January 10, 2011 with respect to Portfolio
          Recovery Associates, Inc.





















































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