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


                                  SCHEDULE 13G
                                 (Rule 13d-102)

   INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT TO RULES 13d-1(b),
      (c), AND (d) AND AMENDMENTS THERETO FILED PURSUANT TO RULE 13d-2(b)
                               (Amendment No. 4)*





                               UNISYS Corporation
-------------------------------------------------------------------------------
                                (Name of Issuer)



                        Common Stock, $0.01 par value
-------------------------------------------------------------------------------
                         (Title of Class of Securities)



                                    909214108
-------------------------------------------------------------------------------
                                 (CUSIP Number)



                                December 31, 2006
-------------------------------------------------------------------------------
             (Date of Event which Requires Filing of this Statement)



Check the appropriate box to designate the rule pursuant to which this Schedule
is filed:

               [   ]   Rule 13d-1(b)

               [ X ]   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).


                                     Page 1



<PAGE>

CUSIP No.         909214108
                  ---------
-------------------------------------------------------------------------------
       1)      Names of Reporting Person

               S.S. or I.R.S. Identification No. of Above Person

                    Tudor Investment Corporation
               ----------------------------------------------------------------
                    22-2514825
               ----------------------------------------------------------------
-------------------------------------------------------------------------------
       2)      Check the Appropriate Box if a Member of a Group (See
               Instructions)
               (a)  -----------------------------------------------------------
               (b)         X
                    -----------------------------------------------------------
-------------------------------------------------------------------------------
       3)      SEC Use Only
                             --------------------------------------------------
-------------------------------------------------------------------------------
       4)      Citizenship or Place of Organization               Delaware
                                                     --------------------------
-------------------------------------------------------------------------------
                           (5)  Sole Voting Power                        0
                                                  -----------------------------
Number of Shares           ----------------------------------------------------
Beneficially               (6)  Shared Voting Power              12,910,461
Owned by Each                                       ---------------------------
Reporting Person           ----------------------------------------------------
With                       (7)  Sole Dispositive Power                   0
                                                       ------------------------
                           ----------------------------------------------------
                           (8)  Shared Dispositive Power         12,910,461
                                                         ----------------------
-------------------------------------------------------------------------------
       9)      Aggregate Amount Beneficially Owned by Each Reporting
               Person                                            12,910,461
                   ------------------------------------------------------------
-------------------------------------------------------------------------------
      10)      Check if the Aggregate Amount in Row (9) Excludes Certain Shares
               (See Instructions)
                                  ---------------------------------------------
-------------------------------------------------------------------------------
      11)      Percent of Class Represented by Amount in Row 9        3.7%
                                                               ----------------
-------------------------------------------------------------------------------
      12)      Type of Reporting Person (See Instructions)     CO
                                                             ------------------
-------------------------------------------------------------------------------


                                     Page 2


<PAGE>


CUSIP No.         909214108
                  ---------
-------------------------------------------------------------------------------
       1)      Names of Reporting Person

               S.S. or I.R.S. Identification No. of Above Person

                    Paul Tudor Jones, II
               ----------------------------------------------------------------

               ----------------------------------------------------------------
-------------------------------------------------------------------------------
       2)      Check the Appropriate Box if a Member of a Group (See
               Instructions)
               (a)  -----------------------------------------------------------
               (b)         X
                    -----------------------------------------------------------
-------------------------------------------------------------------------------
       3)      SEC Use Only
                         ------------------------------------------------------
-------------------------------------------------------------------------------
       4)      Citizenship or Place of Organization               USA
                                                     --------------------------
-------------------------------------------------------------------------------
                           (5)  Sole Voting Power                        0
                                                  -----------------------------
Number of Shares           ----------------------------------------------------
Beneficially               (6)  Shared Voting Power              14,082,674
Owned by Each                                       ---------------------------
Reporting Person           ----------------------------------------------------
With                       (7)  Sole Dispositive Power                   0
                                                       ------------------------
                           ----------------------------------------------------
                           (8)  Shared Dispositive Power         14,082,674
                                                         ----------------------
-------------------------------------------------------------------------------
       9)      Aggregate Amount Beneficially Owned by Each Reporting
               Person                                            14,082,674
                      ---------------------------------------------------------
-------------------------------------------------------------------------------
      10)      Check if the Aggregate Amount in Row (9) Excludes Certain Shares
               (See Instructions)
                                  ---------------------------------------------
-------------------------------------------------------------------------------
      11)      Percent of Class Represented by Amount in Row 9        4.1%
                                                               ----------------
-------------------------------------------------------------------------------
      12)      Type of Reporting Person (See Instructions)     IN
                                                             ------------------
-------------------------------------------------------------------------------


                                     Page 3



<PAGE>



CUSIP No.         909214108
                  ---------
-------------------------------------------------------------------------------
       1)      Names of Reporting Person

               S.S. or I.R.S. Identification No. of Above Person

                    James J. Pallotta
               ----------------------------------------------------------------

               ----------------------------------------------------------------
-------------------------------------------------------------------------------
       2)      Check the Appropriate Box if a Member of a Group (See
               Instructions)
               (a)  -----------------------------------------------------------
               (b)         X
                    -----------------------------------------------------------
-------------------------------------------------------------------------------
       3)      SEC Use Only
                             --------------------------------------------------
-------------------------------------------------------------------------------
       4)      Citizenship or Place of Organization          USA
                                                     --------------------------
-------------------------------------------------------------------------------
                           (5)  Sole Voting Power                        0
                                                  -----------------------------
Number of Shares           ----------------------------------------------------
Beneficially               (6)  Shared Voting Power              14,082,674
Owned by Each                                       ---------------------------
Reporting Person           ----------------------------------------------------
With                       (7)  Sole Dispositive Power                   0
                                                       ------------------------
                           ----------------------------------------------------
                           (8)  Shared Dispositive Power         14,082,674
                                                         ----------------------
-------------------------------------------------------------------------------
       9)      Aggregate Amount Beneficially Owned by Each Reporting
               Person                                            14,082,674
                   ------------------------------------------------------------
-------------------------------------------------------------------------------
      10)      Check if the Aggregate Amount in Row (9) Excludes Certain Shares
               (See Instructions)
                                  ---------------------------------------------
-------------------------------------------------------------------------------
      11)      Percent of Class Represented by Amount in Row 9        4.1%
                                                               ----------------
-------------------------------------------------------------------------------
      12)      Type of Reporting Person (See Instructions)     IN
                                                             ------------------
-------------------------------------------------------------------------------


                                     Page 4



<PAGE>



CUSIP No.         909214108
                  ---------
-------------------------------------------------------------------------------
       1)      Names of Reporting Person

               S.S. or I.R.S. Identification No. of Above Person

                    Tudor Proprietary Trading, L.L.C.
               ----------------------------------------------------------------
                    13-3720063
               ----------------------------------------------------------------
-------------------------------------------------------------------------------
       2)      Check the Appropriate Box if a Member of a Group (See
               Instructions)
               (a)  -----------------------------------------------------------
               (b)         X
                    -----------------------------------------------------------
-------------------------------------------------------------------------------
       3)      SEC Use Only
                             --------------------------------------------------
-------------------------------------------------------------------------------
       4)      Citizenship or Place of Organization          Delaware
                                                     --------------------------
-------------------------------------------------------------------------------
                           (5)  Sole Voting Power                        0
                                                  -----------------------------
Number of Shares           ----------------------------------------------------
Beneficially               (6)  Shared Voting Power                1,172,213
Owned by Each                                       ---------------------------
Reporting Person           ----------------------------------------------------
With                       (7)  Sole Dispositive Power                   0
                                                       ------------------------
                           ----------------------------------------------------
                           (8)  Shared Dispositive Power           1,172,213
                                                         ----------------------
-------------------------------------------------------------------------------
       9)      Aggregate Amount Beneficially Owned by Each Reporting
               Person                                              1,172,213
                      ---------------------------------------------------------
-------------------------------------------------------------------------------
      10)      Check if the Aggregate Amount in Row (9) Excludes Certain Shares
               (See Instructions)
                                  ---------------------------------------------
-------------------------------------------------------------------------------
      11)      Percent of Class Represented by Amount in Row 9        0.3%
                                                               ----------------
-------------------------------------------------------------------------------
      12)      Type of Reporting Person (See Instructions)     OO
                                                             ------------------
-------------------------------------------------------------------------------


                                     Page 5



<PAGE>



CUSIP No.         909214108
                  ---------
-------------------------------------------------------------------------------
       1)      Names of Reporting Person

               S.S. or I.R.S. Identification No. of Above Person

                    The Tudor BVI Global Portfolio Ltd.
               ----------------------------------------------------------------

               ----------------------------------------------------------------
-------------------------------------------------------------------------------
       2)      Check the Appropriate Box if a Member of a Group (See
               Instructions)
               (a)  -----------------------------------------------------------
               (b)         X
                    -----------------------------------------------------------
-------------------------------------------------------------------------------
       3)      SEC Use Only
                             --------------------------------------------------
-------------------------------------------------------------------------------
       4)      Citizenship or Place of Organization            Cayman Islands
                                                     --------------------------
-------------------------------------------------------------------------------
                           (5)  Sole Voting Power                        0
                                                  -----------------------------
Number of Shares           ----------------------------------------------------
Beneficially               (6)  Shared Voting Power                2,215,951
Owned by Each                                       ---------------------------
Reporting Person           ----------------------------------------------------
With                       (7)  Sole Dispositive Power                   0
                                                       ------------------------
                           ----------------------------------------------------
                           (8)  Shared Dispositive Power           2,215,951
                                                         ----------------------
-------------------------------------------------------------------------------
       9)      Aggregate Amount Beneficially Owned by Each Reporting
               Person                                              2,215,951
                      ---------------------------------------------------------
-------------------------------------------------------------------------------
      10)      Check if the Aggregate Amount in Row (9) Excludes Certain Shares
               (See Instructions)
                                  ---------------------------------------------
-------------------------------------------------------------------------------
      11)      Percent of Class Represented by Amount in Row 9        0.6%
                                                               ----------------
-------------------------------------------------------------------------------
      12)      Type of Reporting Person (See Instructions)     CO
                                                             ------------------
-------------------------------------------------------------------------------


                                     Page 6



<PAGE>



CUSIP No.         909214108
                  ---------
-------------------------------------------------------------------------------
       1)      Names of Reporting Person

               S.S. or I.R.S. Identification No. of Above Person

                    The Raptor Global Portfolio Ltd.
               ----------------------------------------------------------------

               ----------------------------------------------------------------
-------------------------------------------------------------------------------
       2)      Check the Appropriate Box if a Member of a Group (See
               Instructions)
               (a)  -----------------------------------------------------------
               (b)         X
                    -----------------------------------------------------------
-------------------------------------------------------------------------------
       3)      SEC Use Only
                             --------------------------------------------------
-------------------------------------------------------------------------------
       4)      Citizenship or Place of Organization         Cayman Islands
                                                     --------------------------
-------------------------------------------------------------------------------
                           (5)  Sole Voting Power                         0
                                                  -----------------------------
Number of Shares           ----------------------------------------------------
Beneficially               (6)  Shared Voting Power              10,600,170
Owned by Each                                       ---------------------------
Reporting Person           ----------------------------------------------------
With                       (7)  Sole Dispositive Power                    0
                                                       ------------------------
                           ----------------------------------------------------
                           (8)  Shared Dispositive Power         10,600,170
                                                         ----------------------
-------------------------------------------------------------------------------
       9)      Aggregate Amount Beneficially Owned by Each Reporting
               Person                                            10,600,170
                      ---------------------------------------------------------
-------------------------------------------------------------------------------
      10)      Check if the Aggregate Amount in Row (9) Excludes Certain Shares
               (See Instructions)
                                  ---------------------------------------------
-------------------------------------------------------------------------------
      11)      Percent of Class Represented by Amount in Row 9        3.1%
                                                               ----------------
-------------------------------------------------------------------------------
      12)      Type of Reporting Person (See Instructions)     CO
                                                             ------------------
-------------------------------------------------------------------------------


                                     Page 7



<PAGE>



CUSIP No.         909214108
                  ---------
-------------------------------------------------------------------------------
       1)      Names of Reporting Person

               S.S. or I.R.S. Identification No. of Above Person

                    The Altar Rock Fund L.P.
               ----------------------------------------------------------------
                    06-1558414
               ----------------------------------------------------------------
-------------------------------------------------------------------------------
       2)      Check the Appropriate Box if a Member of a Group (See
               Instructions)
               (a)  -----------------------------------------------------------
               (b)         X
                    -----------------------------------------------------------
-------------------------------------------------------------------------------
       3)      SEC Use Only
                              -------------------------------------------------
-------------------------------------------------------------------------------
       4)      Citizenship or Place of Organization             Delaware
                                                      -------------------------
-------------------------------------------------------------------------------
                           (5)  Sole Voting Power                      0
                                                  -----------------------------
Number of Shares           ----------------------------------------------------
Beneficially               (6)  Shared Voting Power               94,340
Owned by Each                                       ---------------------------
Reporting Person           ----------------------------------------------------
With                       (7)  Sole Dispositive Power                 0
                                                       ------------------------
                           ----------------------------------------------------
                           (8)  Shared Dispositive Power          94,340
                                                         ----------------------
-------------------------------------------------------------------------------
       9)      Aggregate Amount Beneficially Owned by Each Reporting
               Person                                             94,340
                      ---------------------------------------------------------
-------------------------------------------------------------------------------
      10)      Check if the Aggregate Amount in Row (9) Excludes Certain Shares
               (See Instructions)
                                  ---------------------------------------------
-------------------------------------------------------------------------------
      11)      Percent of Class Represented by Amount in Row 9        0.03%
                                                               ----------------
-------------------------------------------------------------------------------
      12)      Type of Reporting Person (See Instructions)     PN
                                                             ------------------
-------------------------------------------------------------------------------


                                     Page 8



<PAGE>


Item 1(a).     Name of Issuer:

               UNISYS Corporation

Item 1(b).     Address of Issuer's Principal Executive Offices:

               Unisys Way
               Blue Bell, PA  19424

Item 2(a).     Name of Person Filing:

               Tudor Investment Corporation ("TIC")
               Paul Tudor Jones, II
               James J. Pallotta
               Tudor Proprietary Trading, L.L.C. ("TPT")
               The Tudor BVI Global Portfolio Ltd. ("BVI Portfolio")
               The Raptor Global Portfolio Ltd. ("Raptor Portfolio")
               The Altar Rock Fund L.P. ("Altar Rock")

Item 2(b).     Address of Principal Business Office or, if none, Residence:

               The principal business office of each of TIC and TPT
               is:

                           1275 King Street
                           Greenwich, CT 06831

               The principal business office of Mr. Jones and Altar Rock is:

                           c/o Tudor Investment Corporation
                           1275 King Street
                           Greenwich, CT 06831

               The principal business office of Mr. Pallotta is:

                           c/o Tudor Investment Corporation
                           50 Rowes Wharf, 6th Floor
                           Boston, MA 02110

               The principal business office of each of BVI Portfolio and Raptor
               Portfolio is:

                           c/o CITCO
                           Kaya Flamboyan 9
                           P.O. Box 4774
                           Curacao, Netherlands Antilles

Item 2(c).     Citizenship:

               TIC is a Delaware corporation.
               Messrs. Jones and Pallotta are citizens of the United States.
               TPT is a Delaware limited liability company.
               BVI Portfolio and Raptor Portfolio are companies organized under
               the laws of the Cayman Islands.
               Altar Rock is a Delaware limited partnership.

Item 2(d).     Title of Class of Securities:

               Common Stock, par value $0.01


                                     Page 9



<PAGE>


Item 2(e).     CUSIP Number:

               909214108

Item 3. If this statement is filed pursuant to Rules 13d-1(b), or 13d-2(b),
        check whether the person filing is a:
        (a) [ ] Broker or Dealer registered under section 15 of the Act
        (b) [ ] Bank as defined in section 3(a)(6) of the Act
        (c) [ ] Insurance Company as defined in section 3(a)(19) of the Act
        (d) [ ] Investment Company registered under section 8 of the Investment
                Company Act
        (e) [ ] Investment Adviser registered under section 203 of the
                Investment Advisers Act of 1940
        (f) [ ] Employment Benefit Plan, Pension Fund which is subject to the
                provisions of the Employee Retirement Income Security
                Act of 1974 or Endowment Fund; see section 240.13d-1(b)(1)(ii)
                (F)
        (g) [ ] Parent Holding Company, in accordance with section
                240.13d-1(b)(1)(ii)(G) (Note: See Item 7)
        (h) [ ] Group, in accordance with section 240.13d-1(b)(1)(ii)(H)
   
Item 4. Ownership (As of December 31, 2006).

        (a) Amount Beneficially Owned: See Item 9 of cover pages

        (b) Percent of Class: See Item 11 of cover pages

        (c) Number of shares as to which such person has:

            (i)   sole power to vote or to direct the vote

                  See Item 5 of cover pages
                  -------------------------------------------

            (ii)  shared power to vote or to direct the vote

                  See Item 6 of cover pages
                  -------------------------------------------

            (iii) sole power to dispose or to direct the disposition of

                  See Item 7 of cover pages
                  -------------------------------------------

            (iv)  shared power to dispose or to direct the disposition of

                  See Item 8 of cover pages
                  -------------------------------------------

            The shares of Common Stock reported herein as beneficially owned are
         owned directly by TPT (1,172,213 shares), BVI Portfolio (2,215,951
         shares), Raptor Portfolio (10,600,170 shares), and Altar Rock (94,340
         shares). Because TIC provides investment advisory services to BVI
         Portfolio, Raptor Portfolio, and is the general partner of Altar Rock,
         TIC may be deemed to beneficially own the shares of Common Stock owned
         by each of such Reporting Persons. TIC expressly disclaims such
         beneficial ownership. Because Mr. Jones is the controlling shareholder
         of TIC and the indirect controlling equity holder of TPT, Mr. Jones may
         be deemed to beneficially own the shares of Common Stock deemed
         beneficially owned by TIC and TPT. Mr. Jones expressly disclaims such
         beneficial ownership. Because Mr. Pallotta is the portfolio manager of
         TIC and TPT responsible for investment decisions with respect to the
         shares of Common Stock reported herein, Mr. Pallotta may be deemed to
         beneficially own the shares of Common Stock deemed beneficially owned
         by TIC and TPT. Mr. Pallotta expressly disclaims such beneficial
         ownership.

Item 5.  Ownership of Five Percent or Less of a Class.

         If this statement is being filed to report 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 [X]. 

Item 6.  Ownership of More than Five Percent on Behalf of Another Person.

              Not applicable

Item 7.  Identification and Classification of the Subsidiary Which Acquired the
         Security Being Reported on By the Parent Holding Company.



                                    Page 10



<PAGE>

              Not applicable

Item 8.  Identification and Classification of Members of the Group.

              See cover pages

Item 9.  Notice of Dissolution of Group.

              Not applicable


                                    Page 11




<PAGE>

Item 10.  Certification.

            By signing below I certify that, to the best of my knowledge and
belief, the securities referred to above 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.

            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.




                                        Dated:  February 14, 2007


                                        TUDOR INVESTMENT CORPORATION


                                        By:          /s/ Stephen N. Waldman
                                               --------------------------------
                                               Stephen N. Waldman
                                               Managing Director and Associate
                                               General Counsel


                                               /s/ Paul Tudor Jones, II
                                        --------------------------------------
                                               Paul Tudor Jones, II


                                              /s/ James J. Pallotta
                                        ----------------------------------------
                                              James J. Pallotta


                                        TUDOR PROPRIETARY TRADING, L.L.C.


                                        By:          /s/ Stephen N. Waldman
                                               --------------------------------
                                               Stephen N. Waldman
                                               Managing Director and Associate
                                               General Counsel


                                        THE TUDOR BVI GLOBAL PORTFOLIO LTD.

                                        By:      Tudor Investment Corporation,
                                                    Trading Advisor

                                              By:        /s/ Stephen N. Waldman
                                                     --------------------------
                                                     Stephen N. Waldman
                                                     Managing Director and
                                                     Associate General Counsel


                                    Page 12



<PAGE>

                                        THE RAPTOR GLOBAL PORTFOLIO LTD.

                                        By:    Tudor Investment Corporation,
                                                 Investment Adviser


                                              By:        /s/ Stephen N. Waldman
                                                    ---------------------------
                                                    Stephen N. Waldman
                                                    Managing Director and
                                                    Associate General Counsel


                                        THE ALTAR ROCK FUND L.P.

                                        By:    Tudor Investment Corporation,
                                                 General Partner


                                               By:       /s/ Stephen N. Waldman
                                                     --------------------------
                                                     Stephen N. Waldman
                                                     Managing Director and
                                                     Associate General Counsel



                                     Page 13