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. 21)1

Adaptec, Inc.

(Name of Issuer)

Common Stock, par value $0.001

(Title of Class of Securities)

00651F108

(CUSIP Number)

Warren G. Lichtenstein

Steel Partners Holdings L.P.

590 Madison Avenue, 32nd Floor

New York, New York 10022

(212) 520-2300

(Name, Address and Telephone Number of Person

Authorized to Receive Notices and Communications)

June 4, 2010

(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. 00651F108

1	NAME OF REPORTING PERSON STEEL PARTNERS II, L.P.
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 - 0 -
	8	SHARED VOTING POWER 25,214,857
	9	SOLE DISPOSITIVE POWER - 0 -
	10	SHARED DISPOSITIVE POWER 25,214,857
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 25,214,857
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 20.9%
14	TYPE OF REPORTING PERSON PN

2

CUSIP NO. 00651F108

1	NAME OF REPORTING PERSON STEEL PARTNERS HOLDINGS L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) o   (b) o
3	SEC USE ONLY
4	SOURCE OF FUNDS AF
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 - 0 -
	8	SHARED VOTING POWER 25,214,857
	9	SOLE DISPOSITIVE POWER - 0 -
	10	SHARED DISPOSITIVE POWER 25,214,857
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 25,214,857
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 20.9%
14	TYPE OF REPORTING PERSON PN

3

CUSIP NO. 00651F108

1	NAME OF REPORTING PERSON STEEL PARTNERS LLC
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) o   (b) o
3	SEC USE ONLY
4	SOURCE OF FUNDS AF
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 - 0 -
	8	SHARED VOTING POWER 25,214,857
	9	SOLE DISPOSITIVE POWER - 0 -
	10	SHARED DISPOSITIVE POWER 25,214,857
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 25,214,857
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 20.9%
14	TYPE OF REPORTING PERSON OO

4

CUSIP NO. 00651F108

1	NAME OF REPORTING PERSON WARREN G. LICHTENSTEIN
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) o   (b) o
3	SEC USE ONLY
4	SOURCE OF FUNDS AF
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 25,214,857
	9	SOLE DISPOSITIVE POWER - 0 -
	10	SHARED DISPOSITIVE POWER 25,214,857
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 25,214,857
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 20.9%
14	TYPE OF REPORTING PERSON IN

5

CUSIP NO. 00651F108

1	NAME OF REPORTING PERSON JACK L. HOWARD
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 37,500 *
	8	SHARED VOTING POWER - 0 -
	9	SOLE DISPOSITIVE POWER 25,000 **
	10	SHARED DISPOSITIVE POWER - 0 -
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 37,500 *
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) LESS THAN 1%
14	TYPE OF REPORTING PERSON IN

* Represents 18,750 Shares underlying Restricted Stock Awards, 6,250 Shares of which have vested, and 18,750 Shares underlying Non-Qualified Stock Options that are exercisable within 60 days of the date hereof.

** Represents 6,250 Shares underlying Restricted Stock Awards that have vested and 18,750 Shares underlying Non-Qualified Stock Options that are exercisable within 60 days of the date hereof.

6

CUSIP NO. 00651F108

1	NAME OF REPORTING PERSON JOHN J. QUICKE
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 37,500 *
	8	SHARED VOTING POWER - 0 -
	9	SOLE DISPOSITIVE POWER 25,000 **
	10	SHARED DISPOSITIVE POWER - 0 -
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 37,500 *
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES		o
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) LESS THAN 1%
14	TYPE OF REPORTING PERSON IN

* Represents 18,750 Shares underlying Restricted Stock Awards, 6,250 Shares of which have vested, and 18,750 Shares underlying Non-Qualified Stock Options that are exercisable within 60 days of the date hereof.

** Represents 6,250 Shares underlying Restricted Stock Awards that have vested and 18,750 Shares underlying Non-Qualified Stock Options that are exercisable within 60 days of the date hereof.

7

CUSIP NO. 00651F108

The following constitutes Amendment No. 21 to the Schedule 13D filed by the undersigned (“Amendment No. 21”).  This Amendment No. 21 amends the Schedule 13D as specifically set forth.

Item 2. Identity and Background.

Item 2 is hereby amended and restated to read as follows:

(a)           This statement is filed by Steel Partners II, L.P., a Delaware limited partnership (“Steel Partners II”), Steel Partners Holdings L.P., a Delaware limited partnership (“Steel Holdings”), Steel Partners LLC, a Delaware limited liability company (“Partners LLC”), Warren G. Lichtenstein, Jack L. Howard and John J. Quicke.  Each of the foregoing is referred to as a “Reporting Person” and collectively as the “Reporting Persons.”

Steel Holdings is the sole limited partner of Steel Partners II.  Partners LLC is the manager of Steel Partners II and Steel Holdings and has been delegated the sole power to vote and dispose of the securities held by Steel Partners II and Steel Holdings.  Warren G. Lichtenstein is the manager of Partners LLC.  By virtue of these relationships, each of Steel Holdings, Partners LLC and Mr. Lichtenstein may be deemed to beneficially own the Shares owned by Steel Partners II.

Jack L. Howard is the President of Partners LLC.  John J. Quicke is a Managing Director and operating partner of Partners LLC.  Mr. Quicke is the Interim President and Chief Executive Officer and a director of the Issuer and Mr. Howard is a director of the Issuer.  Accordingly, the Reporting Persons are hereby filing a joint Schedule 13D.

Set forth on Schedule A annexed hereto is the name and present principal business, occupation or employment and the name, principal business and address of any corporation or other organization in which such employment is conducted of (i) Steel Partners II GP LLC (“Steel Partners GP”), the general partner of Steel Partners II, (ii) Steel Partners Holdings GP LLC (“Steel Holdings GP”), the general partner of Steel Holdings, (iii) the executive officers of Partners LLC, (iv) the executive officers of Steel Partners GP and (v) the directors of Steel Holdings GP.  To the best of the Reporting Persons’ knowledge, except as otherwise set forth herein, none of the persons or entities listed on Schedule A beneficially owns any securities of the Issuer or is a party to any contract, agreement or understanding required to be disclosed herein.

(b)           The principal business address of each of the Reporting Persons is 590 Madison Avenue, 32nd Floor, New York, New York 10022.

(c)           Steel Holdings is a global diversified holding company that engages or has interests in a variety of operating businesses through its subsidiary companies.  Steel Holdings may seek to obtain majority or primary control, board representation or other significant influence over the portfolio companies in which it holds an interest.  The principal business of Steel Partners II is holding securities for the account of Steel Holdings.  The principal business of Partners LLC is serving as the manager of Steel Partners II and Steel Holdings.  The principal occupation of Warren G. Lichtenstein is serving as the manager of Partners LLC.  The principal occupation of Jack L. Howard is serving as the President of Partners LLC and serving as a principal of Mutual Securities, Inc., a registered broker dealer.  The principal occupation of John J. Quicke is serving as a Managing Director and operating partner of Partners LLC.

8

CUSIP NO. 00651F108

(d)           No Reporting Person nor any person or entity listed on Schedule A 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 or entity listed on Schedule A annexed hereto 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)           Each of the individuals who are Reporting Persons or listed on Schedule A are citizens of the United States of America.  Each of the entities who are Reporting Persons or listed on Schedule A are organized under the laws of the State of Delaware.

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

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

The aggregate purchase price of the 25,214,857 Shares owned by Steel Partners II is approximately $82,334,308, including brokerage commissions.  The Shares owned by Steel Partners II were acquired with partnership funds.

The Shares beneficially owned by Messrs. Howard and Quicke were awarded to them in their capacities as directors of the Issuer.

Set forth on Schedule B annexed hereto is the aggregate purchase price of the Shares beneficially owned, if any, by each of the directors of Steel Holdings GP.

Steel Partners II effects purchases of securities primarily through margin accounts maintained for it with prime brokers, which may extend margin credit to it as and when required to open or carry positions in the margin accounts, subject to applicable federal margin regulations, stock exchange rules and the prime brokers’ credit policies.  In such instances, the positions held in the margin accounts are pledged as collateral security for the repayment of debit balances in the accounts.

Item 5. Interest in Securities of the Issuer.

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

(a)           The aggregate percentage of Shares reported owned by each person named herein is based upon 120,396,971 Shares outstanding, which is the total number of Shares outstanding as of May 12, 2010 as reported in the Issuer’s Form 10-K filed with the Securities and Exchange Commission on May 27, 2010.

As of the close of business on June 7, 2010, Steel Partners II owned directly 25,214,857 Shares, constituting approximately 20.9% of the Shares outstanding.  By virtue of their relationships with Steel Partners II discussed in further detail in Item 2, each of Steel Holdings, Partners LLC and Warren G. Lichtenstein may be deemed to beneficially own the Shares owned by Steel Partners II.

As of the close of business on June 7, 2010, Jack L. Howard beneficially owned 18,750 Shares underlying Restricted Stock Awards, 6,250 Shares of which have vested, and beneficially owned an additional 18,750 Shares underlying Non-Qualified Stock Options that are exercisable within 60 days of the date hereof, constituting in the aggregate less than 1% of the Shares outstanding.

9

CUSIP NO. 00651F108

As of the close of business on June 7, 2010, John J. Quicke beneficially owned 18,750 Shares underlying Restricted Stock Awards, 6,250 Shares of which have vested, and beneficially owned an additional 18,750 Shares underlying Non-Qualified Stock Options that are exercisable within 60 days of the date hereof, constituting in the aggregate less than 1% of the Shares outstanding.

Set forth on Schedule B annexed hereto is the aggregate number and percentage of Shares beneficially owned, if any, by each of the directors of Steel Holdings GP.  Unless otherwise indicated thereon, each of the persons listed on Schedule B has (i) the sole power to vote and dispose of the Shares they beneficially own, if any, and (ii) the right to receive, or the power to direct the receipt of dividends from, or proceeds from the sale of, the Shares that they beneficially own, if any.

Each of the Reporting Persons, as a member of a “group” with the other Reporting Persons for purposes of Rule 13d-5(b)(1) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), may be deemed to beneficially own the Shares owned by the other Reporting Persons.

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

(b)           Each of the Reporting Persons (other than Messrs. Howard and Quicke) may be deemed to have shared power to vote and dispose of the Shares reported in this Schedule 13D owned directly by Steel Partners II.

Jack L. Howard has the sole power to vote and dispose of the Shares underlying the Restricted Stock Awards and Non-Qualified Stock Options owned directly by Mr. Howard.

John J. Quicke has the sole power to vote and dispose of the Shares underlying the Restricted Stock Awards and Non-Qualified Stock Options owned directly by Mr. Quicke.

Item 5(c) is hereby amended to add the following:

(c)           Schedule C annexed hereto lists all transactions in the Shares by the Reporting Persons during the past sixty days.  All of such transactions were effected in the open market.

Item 7. Material to be Filed as Exhibits.

Item 7 is hereby amended to add the following exhibit:

99.1         Powers of Attorney.

10

CUSIP NO. 00651F108

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: June 8, 2010	STEEL PARTNERS II, L.P.
	By:	Steel Partners II GP LLC General Partner
	By:	/s/ Sanford Antignas
		Sanford Antignas Chief Operating Officer

STEEL PARTNERS HOLDINGS L.P.
By:		Steel Partners Holdings GP LLC General Partner
By:	/s/ Sanford Antignas
	Sanford Antignas Chief Operating Officer

STEEL PARTNERS LLC
By:	/s/ Sanford Antignas
	Sanford Antignas Chief Operating Officer

/s/ Sanford Antignas

SANFORD ANTIGNAS

as Attorney-In-Fact for Warren G. Lichtenstein

/s/ Jack L. Howard

JACK L. HOWARD

/s/ Sanford Antignas

SANFORD ANTIGNAS

as Attorney-In-Fact for John J. Quicke

11

CUSIP NO. 00651F108

SCHEDULE A

General Partner of Steel Partners II, L.P.

Name	Present Principal Business	Business Address
Steel Partners II GP LLC	General Partner of Steel Partners II, L.P.	590 Madison Avenue, 32nd Floor New York, NY 10022

General Partner of Steel Partners Holdings L.P.

Name	Present Principal Business	Business Address
Steel Partners Holdings GP LLC	General Partner of Steel Partners Holdings L.P.	590 Madison Avenue, 32nd Floor New York, NY 10022

Executive Officers of Steel Partners LLC

Name and Position	Present Principal Occupation	Business Address
Warren G. Lichtenstein, Chairman and Chief Executive Officer	Chairman and Chief Executive Officer of Steel Partners LLC, a global management firm	c/o Steel Partners LLC 590 Madison Avenue, 32nd Floor New York, NY 10022
Jack L. Howard, President	President of Steel Partners LLC, a global management firm, and a principal of Mutual Securities, Inc., a registered broker dealer	c/o Steel Partners LLC 590 Madison Avenue, 32nd Floor New York, NY 10022
Sanford Antignas, Managing Director, Chief Operating Officer and Secretary	Managing Director, Chief Operating Officer and Secretary of Steel Partners LLC, a global management firm	c/o Steel Partners LLC 590 Madison Avenue, 32nd Floor New York, NY 10022
Michael Falk, Vice President, Chief Financial Officer, Treasurer and Assistant Secretary	Vice President, Chief Financial Officer, Treasurer and Assistant Secretary of Steel Partners LLC, a global management firm	c/o Steel Partners LLC 590 Madison Avenue, 32nd Floor New York, NY 10022

CUSIP NO. 00651F108

Executive Officers of Steel Partners II GP LLC

Name and Position	Present Principal Occupation	Business Address
Warren G. Lichtenstein, Chairman and Chief Executive Officer	Chairman and Chief Executive Officer of Steel Partners LLC, a global management firm	c/o Steel Partners LLC 590 Madison Avenue, 32nd Floor New York, NY 10022
Jack L. Howard, President	President of Steel Partners LLC, a global management firm, and a principal of Mutual Securities, Inc., a registered broker dealer	c/o Steel Partners LLC 590 Madison Avenue, 32nd Floor New York, NY 10022
Sanford Antignas, Managing Director, Chief Operating Officer and Secretary	Managing Director, Chief Operating Officer and Secretary of Steel Partners LLC, a global management firm	c/o Steel Partners LLC 590 Madison Avenue, 32nd Floor New York, NY 10022

Directors of Steel Partners Holdings GP LLC

Name	Present Principal Occupation	Business Address
Anthony Bergamo	Vice Chairman of MB Real Estate, a property management company	c/o MB Real Estate 335 Madison Avenue, 14th Floor New York, NY 10017
John P. McNiff	Partner of Mera Capital Management LP, a private investment partnership	c/o Mera Capital Management LP 161 Washington Street, Suite 1560 Conshohocken, PA 19428
Joseph L. Mullen	Managing Partner of Li Moran International, Inc., a management consulting company	c/o Li Moran International 611 Broadway, Suite 722 New York, NY 10012
General Richard I. Neal	President of Audio MPEG, Inc., a licensor of intellectual property	c/o Audio MPEG, Inc. 66 Canal Center Plaza, Suite 750 Alexandria, VA 22314
Allan R. Tessler	Chairman and Chief Executive Officer of International Financial Group, Inc., an international merchant banking firm	c/o International Financial Group, Inc. 2500 North Moose Wilson Road Wilson, WY 83014
Warren G. Lichtenstein	Chairman and Chief Executive Officer of Steel Partners LLC, a global management firm	c/o Steel Partners LLC 590 Madison Avenue, 32nd Floor New York, NY 10022
Sanford Antignas	Managing Director, Chief Operating Officer and Secretary of Steel Partners LLC, a global management firm	c/o Steel Partners LLC 590 Madison Avenue, 32nd Floor New York, NY 10022

CUSIP NO. 00651F108

SCHEDULE B

Interest in Securities of the Issuer by the Directors of Steel Partners Holdings GP LLC

Name	Number of Shares Beneficially Owned	Percentage	Aggregate Cost
Anthony Bergamo	10	Less than 1%	$7.80

CUSIP NO. 00651F108

SCHEDULE C

Transactions in the Securities of the Issuer

During the Past Sixty Days

Class of Security Securities Purchased Price ($) Date of Purchase

STEEL PARTNERS II, L.P.

Common Stock	100,253	2.8769	06/01/10
Common Stock	200,000	2.9000	06/01/10
Common Stock	45,900	2.8722	06/01/10
Common Stock	58,221	2.9372	06/02/10
Common Stock	72,411	2.9215	06/02/10
Common Stock	100,000	2.9300	06/02/10
Common Stock	31,800	2.9464	06/03/10
Common Stock	73,163	2.9444	06/03/10
Common Stock	100,000	2.9500	06/03/10
Common Stock	300,000	2.9583	06/04/10
Common Stock	168,592	2.9638	06/04/10
Common Stock	273,011	2.9503	06/04/10
Common Stock	74,300	3.0035	06/07/10
Common Stock	107,363	3.0037	06/07/10
Common Stock	40,000	3.0000	06/07/10