ASSUMPTION AGREEMENT

Exhibit 4.3

EXECUTION COPY

ASSUMPTION AGREEMENT

(Second Amended and Restated Guarantee and Collateral Agreement)

      ASSUMPTION AGREEMENT, dated as of April 20, 2005, made by Enterprise Computer Systems, Inc., a South Carolina corporation (the “Additional Grantor”), in favor of JPMORGAN CHASE BANK, N.A., a national banking association formerly known as JPMorgan Chase Bank, as administrative agent (in such capacity, the “Administrative Agent”) for the banks and other financial institutions (the “Lenders”) parties to the Credit Agreement referred to below. All capitalized terms not defined herein shall have the meaning ascribed to them in such Credit Agreement.

W I T N E S S E T H:

      WHEREAS, Cooperative Computing, Inc., a Delaware corporation now known as Activant Solutions Inc. (the “Borrower”), Cooperative Computing Holding Company, Inc., a Delaware corporation now known as Activant Solutions Holdings Inc. (“Holdings”), the Lenders and the Administrative Agent have entered into the Third Amended and Restated Credit Agreement, dated as of July 27, 2003 (as amended, supplemented or otherwise modified from time to time, the “Credit Agreement”);

      WHEREAS, in connection with the Credit Agreement, the Borrower, Holdings and certain of their Affiliates (other than the Additional Grantor) have entered into the Second Amended and Restated Guarantee and Collateral Agreement, dated as of December 3, 2002 (as amended, supplemented or otherwise modified from time to time, the “Guarantee and Collateral Agreement”) in favor of the Administrative Agent for the benefit of the Lenders;

      WHEREAS, the Credit Agreement requires the Additional Grantor to become a party to the Guarantee and Collateral Agreement; and