13D Filing: Starboard Value LP and Quantum Corp (QTM)

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.  9)¹

Quantum Corporation

(Name
of Issuer)

Common Stock,
par value $0.01 per share

(Title of Class of Securities)

747906501

(CUSIP Number)

JEFFREY
C. SMITH

STARBOARD
VALUE LP

777 Third Avenue, 18th Floor

New York, New York 10017

(212) 845-7977

STEVE
WOLOSKY, ESQ.

OLSHAN
FROME WOLOSKY LLP

1325
Avenue of the Americas

New
York, New York 10019

(212)
451-2300

(Name, Address and Telephone Number of Person

Authorized to Receive Notices
and Communications)

November 15, 2017

(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).

^* Represents restricted stock units that have vested
that were granted to Mr. Smith on 09/01/13 and 10/01/14 as compensation for his service on the Board of Directors of the Issuer.

The following constitutes
Amendment No. 9 to the Schedule 13D filed by the undersigned (“Amendment No. 9”). This Amendment No. 9 amends the Schedule
13D as specifically set forth herein.

Item 3 is hereby amended and restated to read
as follows:

The Shares purchased by each
of Starboard V&O Fund, Starboard S 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 to the Schedule 13D, which is incorporated by reference
herein.  The aggregate purchase price of the 534,661 Shares beneficially owned by Starboard V&O Fund is approximately
$5,366,216, excluding brokerage commissions.  The aggregate purchase price of the 119,844 Shares beneficially owned by
Starboard S LLC is approximately $1,221,762, excluding brokerage commissions.   The aggregate purchase price of the 97,846
Shares beneficially owned by Starboard C LP is approximately $954,981, excluding brokerage commissions.  The aggregate
purchase price of the 187,521 Shares held in the Starboard Value LP Account is approximately $1,911,866, excluding brokerage commissions.

The 17,195 Shares beneficially
owned by Mr. Smith represent restricted stock units (“RSUs”) that have vested, which were granted to Mr. Smith as compensation
for his service on the Board of Directors of the Issuer.

Item 5 is hereby amended
and restated to read as follows:

The aggregate percentage
of Shares reported owned by each Reporting Person is based upon 34,673,884 Shares outstanding, which is the total number of Shares
outstanding as of November 3, 2017 as reported in the Issuer’s Quarterly Report on Form 10-Q, filed with the Securities and
Exchange Commission on November 9, 2017.

Percentage: Approximately 1.5%

Percentage: Less than 1%

Percentage: Less than 1%

Percentage: Less than 1%

E.       Starboard R GP

Percentage: Less than 1%

Percentage: Approximately 2.7%

Percentage: Approximately 2.7%

Percentage: Approximately 2.7%

Percentage: Approximately 2.7%

Percentage: Approximately 2.7%

Percentage: Approximately 2.8%

Each Reporting Person,
as a member of a “group” with the other Reporting Persons for the purposes of Section 13(d)(3) of the Securities Exchange
Act of 1934, as amended, may be deemed the beneficial owner of the Shares directly owned by the other Reporting Persons. Each Reporting
Person disclaims beneficial ownership of such Shares except to the extent of his or its pecuniary interest therein.

____________________

* See Mr. Smith’s cover page to this Amendment No. 9 for
details regarding his ownership of RSUs of the Issuer that have vested.

Item 6 is hereby
amended to add the following:

As previously
reported in the Schedule 13D and amendments thereto, the Reporting Persons purchased an aggregate of $35,550,000 principal
amount of 4.50% percent convertible senior notes due November 2017 (the “Notes”). The Notes were convertible at
the Reporting Persons’ option at any time prior to the close of business on the business day immediately preceding
November 15, 2017. The Reporting Persons did not convert the Notes prior to the maturity date and accordingly, as of November
15, 2017, the Notes matured and the Reporting Persons no longer beneficially own the Shares underlying the Notes.

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: November 15, 2017