SUBORDINATED NOTE

    THIS NOTE HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
 AMENDED. IT MAY NOT BE SOLD OR TRANSFERRED IN THE ABSENCE OF REGISTRATION OR
 AN EXEMPTION THEREFROM UNDER SAID ACT AND WITHOUT THE PRIOR WRITTEN CONSENT
                                    OF PAYOR.

                            FEDERAL DATA CORPORATION

                              9% SUBORDINATED NOTE

                              DUE FEBRUARY 17, 2000

$1,000,000                                                  February 17, 1998

            Federal Data Corporation, a Delaware corporation ("Payor"), for
value received, promises to pay Ralph O. Williams, or order, ("Payee") the
principal amount of One Million Dollars ($1,000,000.00), together with accrued
interest thereon, each calculated and payable only as and to the extent set
forth below, including without limitation Section 5 hereof, (the "Note" or
"Subordinated Note"). The principal and interest on this Note is payable in
lawful money of the United States of America in immediately available funds at
11222 River View Drive, Potomac, Maryland 20854 or such other place in the
United States as Payee may from time to time designate in writing to Payor.

            This Note is made pursuant to that certain Stock Purchase Agreement
(the "Agreement"), dated February 17, 1998, by and among Payor, R.O.W. Sciences,
Inc., a Delaware corporation (the "Target"), and Ralph O. Williams, Frederic M.
Cullen, the Trustees of the R.O.W. Sciences ESOP, John C. Smith and Paul H.
Tardif (the "Sellers") pursuant to which Payor has purchased from Sellers all
the issued and outstanding shares of Target, and is the "Note" referred to
therein. Payee is a former shareholder of Target and is receiving this Note
pursuant to the Agreement. Payments under this Note are subject to the right of
Payor to reduce amounts payable under this Note as set forth in Section 5 below,
which right shall be binding upon any holder of the Subordinated Note. All
capitalized term used herein and not defined herein shall have the meanings
assigned to such terms in the Agreement.

1.    Payment of Principal and Interest

      1.1 Calculation and Payment of Interest. Interest on the principal balance
of this Note outstanding from time to time until paid in full shall accrue at
the rate of nine percent (9%) per annum computed on the basis of a 365 or
366-day year, as appropriate, for the actual number of days elapsed, commencing
on the date hereof. Such interest shall be payable semiannually in arrears,
beginning on July 17, 1998 and thereafter on each January 1 and July 1 until the
Maturity Date (as defined herein).

<PAGE>

      1.2 Payment on Maturity Date. The principal balance of, and any accrued
and unpaid interest on, this Note shall be payable on the later of (a) February
17, 2000, and (b) to the extent that any Defense Contract Audit Agency ("DCAA")
or other applicable governmental agency audits of contracts that were in effect
as of the date hereof, constituting part of the Assets under the Agreement, with
agencies of the United States Government remain open on February 17, 2000, a
date reasonably selected by the Payor which would allow for the finalization of
any such DCAA audits (as applicable, the "Maturity Date").

      1.3   Optional Prepayment.

            (a) Payor may, at its option at any time, without premium or
penalty, prepay all or any portion of this Note.

            (b) Any prepayment of this Note shall be applied as follows: first,
to payment of accrued interest; and second, to payment of principal. Upon any
partial prepayment, at the request either of Payee or Payor, this Note shall be
surrendered to Payor in exchange for a substitute note, which shall set forth
the revised principal amount but otherwise identical to this Note. In the event
that this Note is prepaid in its entirety, this Note shall be surrendered to
Payor for cancellation as a condition to any such prepayment.

      1.4 Payment Only on Business Days. Any payment hereunder which, but for
this Section 1.4, would be payable on a day which is not a Business Day, shall
instead be due and payable on the Business Day next following such date for
payment.

2.    Events of Default

The following shall constitute "Events of Default" under this Note:

            (a) Subject to Section 4 below, failure by Payor to make any payment
required under this Note when the same shall become due and payable (whether at
maturity, by acceleration or otherwise) and the continuation of such failure for
a period of thirty (30) days; or

            (b) Payor breaches any covenant under Section 3.1, Section 3.2, or
the last sentence of Section 7.9 of this Note, which breach or failure, if
curable, shall continue uncured for a period of thirty (30) days after the date
on which written notice specifying such breach, and stating that such notice is
a "Notice of Default" hereunder, shall have been given by Payee to Payor; or

            (c) Payor, pursuant to or within the meaning of any Bankruptcy Law:

                  (A) commences a voluntary case or proceeding;

                  (B) consents to the entry of an order for relief against it in
an involuntary case or proceeding;


                                       2
<PAGE>

                  (C) consents to the appointment of a Custodian of it or for
all or any substantial portion of its property or assets;

                  (D) makes a general assignment for the benefit of the
creditors; or

            (d) an involuntary case or proceeding is commenced against Payor
under any Bankruptcy Law and is not dismissed, bonded or discharged within
ninety (90) days thereafter, or a court of competent jurisdiction enters an
order or decree under any Bankruptcy Law that:

                  (A) is for relief against Payor in an involuntary case or
proceeding;

                  (B) appoints a Custodian of Payor for all or substantially all
of its properties; or

                  (C) orders the liquidation of Payor;


and in each case the order or decree remains unstayed and in effect for ninety
(90) days; or

            (e) the occurrence of any merger or consolidation with, or any sale
of all or substantially all of the assets of the Payor (a "Business
Combination"), to any other corporation or business entity, which Business
Combination results in a Change in Control of the Payor. For purposes hereof, a
"Change in Control" means (A) any Business Combination other than a Business
Combination in which the shareholders who were shareholders of the Payor
immediately prior to such event have, directly or indirectly, at least a
majority of the voting common equity of the continuing or surviving corporation
immediately after such Business Combination and the conditions stated in clauses
(X) and (Y) below are met, or (B) any Business Combination (1) in which the
Payor is not the continuing or surviving corporation or (2) pursuant to which
the Payor's capital stock would be converted into cash, securities or other
property, except that a Change of Control shall not include any Business
Combination in which, (X) the relative economic values of the respective
interests in the continuing or surviving corporation of the shareholders of the
corporation who were shareholders immediately prior to such Business Combination
plus the consideration received by such Shareholders in connection with the
Business Combination is approximately equal to the relative economic values of
their respective equity interests in the Payor immediately prior to such
Business Combination and (Y) the charter of such continuing or surviving
corporation contains provisions substantially similar to the Payor's Certificate
of Incorporation, reserving rights to each shareholder substantially similar to
the existing rights of such shareholder prior to the Business Combination.

            If an Event of Default specified in Section 2(a), 2(b) or 2(e) shall
have occurred and be continuing and any Senior Debt should then be outstanding,
subject to the provisions of Section 4 hereof, Payee may, at its option, by
notice in writing to Payor and to the Agent under the Senior Debt Documents (the
"Acceleration Notice"), declare the entire principal amount of this Note and the
interest accrued thereon to be due and payable upon the earlier of (i) one
hundred fifty (150) days after the receipt of the Acceleration Notice by Payor
and the Agent


                                       3
<PAGE>

under the Senior Debt Documents or (ii) an acceleration under the Senior Debt
Documents, and upon any such declaration the same shall become due and payable
at such time. If an Event of Default specified in Section 2(a), 2(b) or 2(e)
shall have occurred and be continuing and no Senior Debt shall then be
outstanding, Payee may, at its option, declare the entire principal amount of
this Note and the interest accrued thereon to be due and payable upon the date
which is five (5) Business Days after the date of delivery by Payee to Payor of
a written notice of acceleration, and upon any such declaration the same shall
become due and payable at such time. If an Event of Default specified in Section
2(c) or 2(d) hereof occurs, the principal balance of and accrued interest on
this Note shall become due and payable immediately without any declaration or
other act on the part of Payee.

            If any Event of Default shall have occurred and be continuing,
subject to the provisions of Sections 2 and 4 hereof, Payee may proceed to
protect and enforce its rights either by suit in equity or by action at law, or
both, whether for specific performance of any provision of this Note or in aid
of the exercise of any power granted to Payee under this Note.

3.    Covenants.

      3.1 Affirmative Covenant. Payor covenants and agrees that for so long as
any indebtedness evidenced by this Note shall remain outstanding, unless waived
by Payee, Payor shall: promptly give notice to Payee of (i) any default or Event
of Default hereunder (ii) any notice of an "Event of Default" (as defined in the
Senior Debt Documents) permitting the holder or holders of the Senior Debt to
accelerate such Senior Debt given to Payor by any holder of Senior Debt or its
agent or (iii) any acceleration of the Senior Debt or any other Indebtedness of
Payor having an aggregate principal amount in excess of $5,000,000.

      3.2 Negative Covenants. Payor covenants and agrees that for so long as any
indebtedness evidenced by this Note remains outstanding, Payor will not, without
the written consent of Payee:

            (a) liquidate, wind up or dissolve itself (or suffer any liquidation
or dissolution), or convey, sell, lease, transfer or otherwise dispose of, in
one transaction or a series of related transactions, all or substantially all of
its assets; provided, however, that the foregoing shall not apply in any way to
the grant of a lien or security interest in, or the foreclosure, sale or other
disposition of, collateral pledged to secure Senior Debt pursuant to any
judicial proceeding or by or at the direction of the holders of any Senior Debt
or any agent or other representative acting on their behalf; or

            (b) consolidate with, or merge with or into, any Person unless (i)
Payor shall be the continuing Person, or the Person (if other than Payor) formed
by such consolidation or into which Payor is merged shall be a corporation
organized and existing under the laws of the United States or any state thereof
or of the District of Columbia and, in the event Payor is merged with or into
any other Person, such Person shall expressly assume, by an agreement executed
and delivered to Payee, the obligations of Payor under this Note. Upon any
consolidation or merger


                                       4
<PAGE>

of Payor in accordance with this Section 3.2(b), the successor corporation
formed by such consolidation or into which Payor is merged shall succeed to, and
be substituted for, and may exercise every right and power of, Payor under this
Note with the same effect as if such successor corporation had been named as
Payor herein.

4.    Subordination

      4.1 Note Subordinated to Senior Debt. To the extent and in the manner
hereinafter set forth in this Section 4 and subject to the terms of Section 5
below, the indebtedness represented by this Note and the payment of the
principal of and the interest on this Note and any claim for rescission of the
purchase of this Note, and any claim (such as a claim in a bankruptcy or similar
proceeding) which is the equivalent of or substitute for principal of or
interest on this Note, and all other payments with respect to or on account of
this Note (collectively, the "Subordinated Debt") (a) rank, notwithstanding any
provisions to the contrary in such notes, pari passu in right of payment with
the subordinated notes issued by Payor (i) pursuant to that certain Agreement
and Plan of Merger dated April 9, 1997 by and among Azmat Ali, Peter Belford,
Arthur Vebin, NYMA, Inc. and NYMA Acquisition, Inc., and Peter Belford as the
initial shareholder representative; (ii) pursuant to that Stock Purchase
Agreement dated June 18, 1997 by and among Payor and Gary S. and Areather T.
Murray, William S. Strang, Holton B. Shipman, Jr., James K. White, Peter A.
Perucci, Myron P. Erkiletian and Sylvest Management Systems Corporation; and
(iii) in the offering by Payor of 10-1/8% Senior Subordinated Notes due 2005 or
the 10-1/8% Senior Subordinated Notes due 2005 issued in exchange therefor, and
(b) are hereby expressly made subordinate and subject in right of payment to the
prior payment in full in cash of all other Senior Debt. This Section 4 shall
inure to the benefit of all Persons who become holders of, or continue to hold,
Senior Debt, each of whom is an obligee hereunder and is entitled to enforce
such holder's rights under this section 4, subject to the provisions hereof,
without any act or notice of acceptance hereof or reliance hereon. For purposes
of this Section 4, Senior Debt shall not be deemed to have been paid in full
until the termination of all commitments or other obligations by any holder
thereof and unless all such holders shall have received indefeasible payment in
full in cash of all obligations under or in respect of Senior Debt (including,
without limitation, Post Petition Interest).

      4.2 No Payment on Note in Certain Circumstances.

            (a) During the continuance of any default in the payment of any
Senior Debt, whether at maturity, upon redemption or pursuant to acceleration or
otherwise (each, a "Payment Default"), no direct or indirect payment of any kind
shall be made, asked for, demanded, accepted, received or retained with respect
to principal, interest or other amounts due under the Note nor shall any holder
thereof exercise any remedies with respect thereto.

            (b) Upon the occurrence of any default (other than a Payment
Default) under any Senior Debt Document which would permit the Banks (or any
other holder of Senior Debt) to accelerate the maturity of the Senior Debt
outstanding thereunder (whether after the giving of notice, the lapse of time,
or both or otherwise) (each, a "Non-Payment Default"), no payment or


                                       5
<PAGE>

distribution (including any payment or distribution that may be payable by
reason of any other indebtedness of Payor being subordinated to payment of the
Subordinated Debt) shall be made by or on behalf of Payor for or on account of
or in respect of the Subordinated Debt until such Non-Payment Default shall have
been cured or waived or otherwise ceases to exist pursuant to the terms of such
Senior Debt, or the benefits of this sentence shall have been waived by or on
behalf of, and at the sole option of, the holders of a majority of the principal
amount of such Senior Debt. Notwithstanding the foregoing, the suspension of
payments described in the preceding sentence shall terminate, and the Payor
shall be obligated to make all payments of principal and interest on this Note,
including any payments not made by virtue of such suspension, if any holder or
holders of the relevant Senior Debt has not, on or prior to the 180th day after
the occurrence of the Non-Payment Default under the Senior Debt, declared all
unpaid principal and interest on such Senior Debt to be immediately due and
payable, unless such Non-Payment Default shall have been cured or waived or
otherwise ceases to exist pursuant to the terms of such Senior Debt, or the
benefits of the previous sentence shall have been waived by or on behalf of, and
at the sole option of, the holders of a majority of the principal amount of such
Senior Debt.

            (c) Payee agrees that, so long as payments or distributions for or
on account of the Subordinated Debt are not permitted pursuant to this Section
4, Payee will not take, sue for, ask or demand from Payor payment of all or any
amounts under or in respect of this Note, or commence, or join with any creditor
other than the holders of Senior Debt and their agents in commencing, directly
or indirectly cause Payor to commence, or assist Payor in commencing, any
proceeding referred to in Section 4.3, and Payee shall not take or receive from
Payor, directly or indirectly or on its behalf, in cash or other property or by
set-off (except in respect to Payor's rights as set forth in Section 5 below) or
in any other manner, including, without limitation, from or by way of
collateral, payment of all or any amounts under or in respect of the
Subordinated Debt. In the event that notwithstanding the foregoing provisions of
this Section 4.2, any payment or distribution of any kind or character, whether
in cash, property or securities (including any payment or distribution that may
be payable by reason of any other indebtedness of Payor being subordinated to
payment of the Subordinated Debt), shall be received by Payee for or on account
of or in respect of the Subordinated Debt before all Senior Debt is indefeasibly
paid in full, such payment or distribution shall be received and held in trust
for, and shall be paid over (in the same form as so received, to the extent
practicable, and with any necessary endorsement) to the holders of the Senior
Debt remaining unpaid or their representative or representatives, or to the
trustee or trustees under any such indenture or agreement under which any Senior
Debt may have been issued, for application (in the case of cash) to, or as
collateral (in the case of non-cash property or securities) for the payment or
prepayment of Senior Debt, until all Senior Debt shall have been paid in full in
cash, after giving effect to any concurrent payment or distribution to the
holders of such Senior Debt.

      4.3 Dissolution; Liquidation; Bankruptcy; Acceleration. In the event of
(i) any insolvency or bankruptcy case or proceeding, or any receivership,
liquidation, reorganization or other similar proceeding in connection therewith,
relative to the Payor or any of its assets, or (ii) any liquidation, dissolution
or other winding up of the Payor, whether voluntary or involuntary or


                                       6
<PAGE>

whether or not involving insolvency or bankruptcy, or (iii) any assignment for
the benefit of creditors or any other marshalling of assets or liabilities of
the Payor, or (iv) the acceleration of the Senior Debt by reason of the
occurrence of a default or an event of default thereunder (each such event, if
any, herein sometimes referred to as a "Proceeding"):

            (a) The holders of all Senior Debt shall first be entitled to
receive payment in full in cash of all Senior Debt before any direct or indirect
payment may be made for or on account of payments under or in respect of the
Subordinated Debt, whether in cash, property or securities of any kind;

            (b) Any payment or distribution of any kind or character, whether in
cash, property or securities (including any payment or distribution that may be
payable by reason of any other indebtedness of Payor being subordinated to
payment of the Subordinated Debt), to which Payee would be entitled except for
the provisions of this Section 4, shall be paid by the liquidating trustee or
agent or other person making such payment or distribution, whether a trustee in
bankruptcy, a receiver or liquidating trustee or other trustee or agent,
directly to the holders of Senior Debt or their representative or
representatives, or to the trustee or trustees under any indenture under which
any instrument evidencing any of such Senior Debt may have been issued for
application (in the case of cash) to, or as collateral (in the case of non-cash
property or securities) for the payment or prepayment of Senior Debt, to the
extent necessary to make payment in full of all Senior Debt remaining unpaid,
after giving effect to any concurrent payment or distribution to the holders of
such Senior Debt.

            (c) The holders of Senior Debt are hereby irrevocably authorized and
empowered (in their own names or in the name of Payee or otherwise), but shall
have no obligation, to demand, sue for, collect and receive every payment or
distribution referred to in paragraph (b) above and give acquittance therefor
and to file claims and proofs of claim and take such other action (including,
without limitation, voting the amounts owing under the Subordinated Debt or
enforcing any security interest or other lien securing payment of the amounts
owing under the Subordinated Debt) as they may deem necessary or advisable for
the exercise or enforcement of any of the rights or interests of the holders of
Senior Debt hereunder.

            (d) Payee shall duly and promptly take such action as the holders of
Senior Debt may reasonably request to execute and deliver to the holders of
Senior Debt such powers of attorney, assignments, or other instruments as the
holders of Senior Debt may request in order to enable the holders of Senior Debt
to enforce any and all claims with respect to, and any security interests and
other liens securing payment of, the amounts owing under the Subordinated Debt.

            (e) In the event that, notwithstanding the foregoing provisions of
this Section 4.3, any payment or distribution of any kind or character, whether
in cash, property or securities (including any payment or distribution that may
be payable by reason of any other indebtedness of Payor being subordinated to
payment of the Subordinated Debt), shall be received by Payee for or on account
of or in respect of the Subordinated Debt before all Senior Debt is indefeasibly
paid in full, such payment or distribution shall be received and held in trust
for, and shall be paid


                                       7
<PAGE>

over (in the same form as so received, to the extent practicable, and with any
necessary endorsement) to the holders of the Senior Debt remaining unpaid or
their representative or representatives, or to the trustee or trustees under any
such indenture or agreement under which any Senior Debt may have been issued,
for application (in the case of cash) to, or as collateral (in the case of
non-cash property or securities) for the payment or prepayment of Senior Debt,
until all Senior Debt shall have been paid in full in cash, after giving effect
to any concurrent payment or distribution to the holders of such Senior Debt.

      4.4 Subrogation. Upon the final payment in full in cash of all Senior
Debt, Payee shall be subrogated to the rights of the holders of Senior Debt to
receive payments or distributions of cash, property or securities of Payor
applicable to the Senior Debt until the principal of and interest on and all
other amounts payable under the Subordinated Debt shall be paid in full, and for
the purposes of such subrogation, no payments or distributions to the holders of
the Senior Debt of any cash, property or securities to which Payee would be
entitled except for the provisions of this Section 4 and no payment over
pursuant to the provisions of this Section 4 to the holders of Senior Debt by
Payee shall, as between Payor, its creditors other than holders of Senior Debt,
and Payee, be deemed to be a payment by Payor to or on account of the
Subordinated Debt. It is understood that the provisions of this Section 4 are
and are intended solely for the purpose of defining the relative rights of
Payee, on the one hand, and the holders of the Senior Debt, on the other hand.

      4.5 Obligations of Payor Unconditional. Nothing contained in this Section
4 or elsewhere in this Note is intended to or shall impair, as among Payor, its
creditors other than the holders of Senior Debt, and Payee, the obligation of
Payor, which is absolute and unconditional, to pay to Payee the principal of and
interest on and all other amounts due under this Note in accordance with its
terms, or is intended to or shall affect the relative rights of Payee and
creditors of Payor other than the holders of the Senior Debt, nor shall anything
herein prevent Payee from exercising all remedies otherwise permitted by
applicable law upon default under this Note, subject to the provisions of this
Section 4 and to the rights of holders of Senior Debt to receive distributions
and payments otherwise payable to Payee.

      4.6 Reliance on Judicial Order or Certificate of Liquidating Agent. Upon
any payment or distribution of assets of Payor referred to in this Section 4,
Payee shall be entitled to rely upon any order or decree made by any court of
competent jurisdiction in which bankruptcy, dissolution, winding-up, liquidation
or reorganization proceedings are pending, or a certificate of the receiver,
trustee in bankruptcy, liquidating trustee, agent or other person making such
payment or distribution, delivered to Payee, for the purpose of ascertaining the
persons entitled to participate in such distribution, the holders of the Senior
Debt and other indebtedness of Payor, the amount thereof or payable thereon, the
amount or amounts paid or distributed thereon and all other facts pertinent
thereto or to Section 4 of this Note. Such reliance shall not affect the rights
of the holders of the Senior Debt.

      4.7 Subordination Rights Not Impaired by Acts or Omissions of Payor or
Holders of Senior Debt. No right of any present or future holders of any Senior
Debt to enforce


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<PAGE>

subordination as provided herein will at any time in any way be prejudiced or
impaired by any act or failure to act on the part of Payor or by any act or
failure to act by any such holder, or by any act, failure to act or
noncompliance by Payor, the holders of Senior Debt or their respective agents
with the terms of this Note, regardless of any knowledge thereof which any such
holder or Payor may have or otherwise be charged with. No amendment, waiver or
other modification of this Note shall in any way adversely affect the rights of
the holders of any Senior Debt under this Section 4 unless such holders of
Senior Debt consent in writing to such amendment, waiver or modification. The
provisions of this Section 4 are intended for the benefit of and shall be
enforceable directly by the holders of the Senior Debt.

      4.8 Further Assurances. Payee and Payor each will, at Payor's expense and
at any time and from time to time, promptly execute and deliver all further
instruments and documents, and take all further action, that may be necessary or
desirable, or that the holders of Senior Debt may request, in order to protect
any right or interest granted or purported to be granted hereby or to enable the
holders of Senior Debt to exercise and enforce their rights and remedies
hereunder.

      4.9 Agreements in Respect of Subordinated Debt.

            (a) Payor agrees that it will not make any payment for or on account
of or in respect of this Note, or take any other action, in contravention of the
provisions of this Section 4.

            (b) Payee shall promptly notify the holders of Senior Debt, at
Bankers Trust Company, 130 Liberty Street, New York, NY 10006, or such other
address of which Payee has been notified in writing, of the occurrence of any
default under this Note of which Payee shall obtain knowledge.

      4.10 Obligations Hereunder Not Affected. All rights and interests of the
holders of Senior Debt hereunder, and all agreements and obligations of Payee
and Payor under this Section 4, shall remain in full force and effect
irrespective of:

            (i) any lack of validity or enforceability of any Senior Debt
      Document;

            (ii) any change in the time, manner or place of payment of, or in
      any other term of, all or any of the Senior Debt, or any other amendment
      or waiver of or any consent to any departure from any Senior Debt
      Document, including, without limitation, any increase in the Senior Debt
      resulting from the extension of additional credit to Payor or any of its
      Subsidiaries or otherwise;

            (iii) any taking, exchange, release or non-perfection of any other
      collateral, or any taking, release, amendment or waiver of or consent to
      departure from any guaranty, for all or any of the Senior Debt;

            (iv) any manner of application of collateral, or proceeds thereof,
      to all or any of the Senior Debt, or any manner of sale or other
      disposition of any collateral for all or any of the Senior Debt or any
      other assets of Payor or any of its Subsidiaries;


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<PAGE>

            (v) any change, restructuring or termination of the corporate
      structure or existence of Payor or any of its Subsidiaries; or

            (vi) any other circumstance which might otherwise constitute a
      defense available to, or a discharge of, Payor or a subordinated creditor.

The provisions of this Section 4 shall continue to be effective or be
reinstated, as the case may be, if at any time any payment of any of the Senior
Debt is rescinded or must otherwise be returned by the holders of Senior Debt
upon the insolvency, bankruptcy or reorganization of Payor or otherwise, all as
though such payment had not been made.

      4.11 Waiver. Payee and Payor each hereby waives promptness, diligence,
notice of acceptance and any other notice with respect to any of the Senior Debt
and this Section 4 and any requirement that the holders of Senior Debt protect,
secure, perfect or insure any security interest or lien on any property subject
thereto or exhaust any right or take any action against Payor or any other
person or entity or any collateral.

      4.12 No Waiver; Remedies. No failure on the part of the holders of Senior
Debt to exercise, and no delay in exercising, any right hereunder shall operate
as a waiver thereof; nor shall any single. or partial exercise of any right
hereunder preclude any other or further exercise thereof or the exercise of any
other right. The remedies herein provided are cumulative and not exclusive of
any remedies provided by law.

      4.13 Continuing Agreement, Assignments Under Senior Debt Agreements. The
provisions of this Section 4 constitute a continuing agreement and shall (i)
remain in full force and effect until the indefeasible payment in full in cash
of the Senior Debt, (ii) be binding upon Payee, Payor and their respective
successors and assigns, and (iii) inure to the benefit of, and be enforceable
by, the holders of Senior Debt and their successors, transferees and assigns.
Without limiting the generality of the foregoing clause (iii), the holders of
Senior Debt may assign or otherwise transfer all or any portion of their rights
and obligations under any Senior Debt Document, as applicable, to any other
person or entity, and such other person or entity shall thereupon become vested
with all the rights in respect thereof granted to the holders of Senior Debt
herein or otherwise.

5. Right to Reduce Amounts Payable Under this Note. Payee hereby agrees, by
acceptance of this Note, that Payor may reduce the principal amount of this Note
or withhold certain payments under this Note following the Closing pursuant to
Section 9(g) of the Agreement, subject to such other terms and conditions as are
set forth in the Agreement. Any such adjustment is intended as, and shall be
treated by the parties as, an adjustment to the Purchase Price. If the principal
amount of the Note is reduced pursuant to Subsection 9(g) of the Agreement, such
reduction shall be deemed to be made effective as of the Closing Date and all
interest that may have accrued on the principal amount so cancelled shall also
be deemed to be retroactively cancelled, effective as of the earlier of (i) the
date hereof and (ii) the date such Claim arose. To the extent any such reduction
would have caused any interest payment


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<PAGE>

theretofore made on this Note not to have been payable, or to have been reduced,
the amount of any such payment in excess of what would have been payable had
such reduction actually been made on the Closing Date shall be set off against
and reduce the amount of each payment thereafter paid hereunder until the full
amount of such excess has been recovered by Payor. Upon any reduction of the
principal amount of the Note, Payee, shall, upon request of the Payor, surrender
this Note and Payor shall issue a replacement Note to Payee, upon such
surrender, to reflect such decrease in principal amount but otherwise identical
to this Note.

6.    Certain Definitions

            "Agent" means Bankers Trust, as agent for the lenders under the
Senior Debt, and its successors and assigns.

            "Bankruptcy Law" means Title II, United States Code, or any similar
federal, state or foreign law for the relief of debtors or any arrangement,
reorganization, assignment for the benefit of creditors or any other marshalling
of the assets and liabilities of Payor.

            "Business Day" means each day other than Saturdays, Sundays and days
when commercial banks are authorized or required by law to be closed for
business in New York, New York.

            "Credit Agreement" means the Credit Agreement dated July 25, 1997
among the Payor, Bankers Trust Company, as agent thereunder, and the other
parties thereto, together with the related documents thereto (including without
limitation any guarantee agreements and security documents), in each case as
such agreement or document may be amended, modified or supplemented from time to
time, including without limitation any agreement or document extending the
maturity of, refinancing, replacing or otherwise restructuring all or any part
of the Indebtedness under such agreement or document or any replacement or
successor agreement or document and whether by the same or any other agent,
lender or group of lenders.

            "Custodian" means any receiver, trustee, assignee, liquidator,
custodian or similar official under any Bankruptcy Law.

            "Event of Default" to means any of the occurrences specified under
Sections 2(a) through 2(e) of this Note.

            "Indebtedness" of any Person means all obligations of such Person
for borrowed money or evidenced by bonds, notes, debentures or similar
instruments, excluding notes and capital leases issued in connection with
offsetting lease assets and excluding all other capitalized lease obligations.

            "Person" means any individual, corporation, partnership, joint
venture, association, joint-stock company, trust, unincorporated organization or
government or any agency or political subdivision thereof.


                                       11
<PAGE>

            "Refinancing Debt" means any indebtedness incurred to repay,
refinance or otherwise replace indebtedness or obligations (including, without
limitation, commitments) under the Credit Agreement.

            "Senior Debt" means all obligations of Payor (including without
limitation contingent obligations with respect to undrawn letters of credit
issued under the Credit Agreement, any obligations owed with respect to
indemnification obligations, interest rate protection incurred to satisfy the
requirements of the Credit Agreement and commitment fees and agency fees payable
thereunder or pursuant thereto) (i) under the Credit Agreement or (ii) with
respect to Refinancing Debt (including in each such case fees, expenses, claims,
charges, indemnity obligations and interest at the contract rate (including any
rate applicable upon default) accrued or accruing after the commencement of a
Proceeding whether or not such interest is an allowed claim enforceable against
the debtor in a bankruptcy case under Title II of the United States Code or
whether or not such interest accrues after the filing of such petition for
purposes of such Title ("Post Petition Interest"). Senior Debt outstanding under
or in respect of Senior Debt Documents shall continue to constitute Senior Debt
notwithstanding that such Senior Debt may be disallowed, avoided or subordinated
pursuant to any Bankruptcy Law or other applicable insolvency law or equitable
principles.

            "Senior Debt Documents" means the Credit Agreement and any other
agreement, indenture, mortgage, guaranty, pledge, security agreement or
instrument evidencing or securing Senior Debt or pursuant to which Senior Debt
is incurred.

            "Subordinated Note" means this Note.

7.    Miscellaneous

      7.1 Section Headings. The section headings contained in this Note are for
reference purposes only and shall not affect the meaning or interpretation of
this Note.

      7.2 Amendment and Waiver. Subject to Section 7.10 hereof, no provision of
this Note may be amended or waived unless Payor shall have obtained the written
agreement of Payee and (unless there are no amounts and no commitments
outstanding under the Senior Debt) the Agent. No failure or delay in exercising
any right, power or privilege hereunder shall imply or otherwise operate as a
waiver of any rights of Payee, nor shall any single or partial exercise thereof
preclude any other or future exercise thereof or the exercise of any other
right, power or privilege.

      7.3 Successors, Assigns and Transferors. This Note may not be assigned or
transferred by Payee without the express written consent of Payor and may not be
assigned or transferred to (x) any competitor, customer or supplier of Payor or
any of its Subsidiaries or (y) to any other Person if such assignment or
transfer would cause any interest payments due under this Note to become
non-deductible as an expense for any tax purposes. Payor may not assign its
obligations under this Note without the prior written consent of Payee except in
connection with


                                       12
<PAGE>

a transaction permitted under Section 3.2(b) hereof. Subject to the foregoing,
the obligations of Payor and Payee under this Note shall be binding upon, and
inure to the benefit of, and be enforceable by, Payor and Payee, and their
respective successors and permitted assigns, whether or not so expressed.

      7.4 Governing Law. This Note shall be governed by, and construed in
accordance with, the laws of the State of Maryland without giving effect to any
conflicts of laws principles thereof that would otherwise require the
application of the law of any other jurisdiction.

      7.5 Lost, Stolen, Destroyed or Mutilated Note. Upon receipt of evidence
reasonably satisfactory to Payor of the loss, theft, destruction or mutilation
of this Note and of indemnity arrangements reasonably satisfactory to Payor from
or on behalf of the holder of this Note, and upon surrender or cancellation of
this Note if mutilated, Payor shall make and deliver a new note of like tenor in
lieu of such lost, stolen, destroyed or mutilated Note, at Payee's expense.

      7.6 Waiver of Presentment, Etc. Except as otherwise provided herein,
presentment, demand, protest, notice of dishonor and all other notices are
hereby expressly waived by Payor.

      7.7 Usury. Nothing contained in this Note shall be deemed to establish or
require the payment of a rate of interest in excess of the maximum rate legally
enforceable. If the rate of interest called for under this Note at any time
exceeds the maximum rate legally enforceable, the rate of interest required to
be paid hereunder shall be automatically reduced to the maximum rate legally
enforceable. If such interest rate is so reduced and thereafter the maximum rate
legally enforceable is increased, the rate of interest required to be paid
hereunder shall be automatically increased to the lesser of the maximum rate
legally enforceable and the rate otherwise provided for in this Note.

      7.8 Notices. Any notice, request, instruction or other document to be
given hereunder by either party to the other shall be in writing and shall be
deemed given when received and shall be (i) delivered personally or (ii) mailed
by certified mail, postage prepaid, return receipt requested or (iii) delivered
by Federal Express or a similar overnight courier or (iv) sent via facsimile
transmission to the fax number given below, as follows:

            If to Payor, addressed to:

                  Federal Data Corporation
                  4800 Hampden Lane
                  Bethesda, MD 20814
                  Attention: James M. Dean
                  Fax Number: (301) 961-7042


                                       13
<PAGE>

            With a copy to:

                  The Carlyle Group, L.P.
                  1001 Pennsylvania Avenue, N.W.
                  Suite 220 South
                  Washington, DC 20004
                  Attention:   Peter J. Clare
                  Fax Number: (202) 347-1818

                        and

                  Shaw Pittman Potts & Trowbridge
                  2300 N Street, N.W.
                  Washington, D.C.  20037
                  Attention:  Victoria J. Perkins, Esq.
                  Fax Number:  (202) 663-8007

            If to Payee, addressed to:

                  Mr. Ralph O. Williams
                  11222 River View Drive
                  Potomac, MD 20854

            With a copy to:

                  Kirkpatrick & Lockhart LLP
                  1800 Massachusetts Avenue, N.W.
                  2nd Floor
                  Washington, D.C.  20036
                  Attention:  Alan J. Berkeley, Esq.
                  Fax Number:  (202) 778-9100


or to such other place and with such other copies as either party may designate
as to itself by written notice to the other party.

            In the event that any notice under this Note is required to be made
on or as of a day which is not a Business Day, then such notice shall not be
required to be made until the first day thereafter which is a Business Day.

7.9 Representations and Warranties and Covenant of Payor. Payor hereby
represents and warrants to Payee that: (a) Payor is duly incorporated, validly
existing and in good standing under the laws of the State of Delaware; (b) Payor
has duly authorized, executed and delivered this Note; and (c) this Note
constitutes a legally valid and binding obligation of Payor, enforceable against
Payor in accordance with its terms, subject to the effect of bankruptcy,


                                       14
<PAGE>

insolvency, reorganization, moratorium or other similar laws now or hereafter in
effect relating to or affecting the rights or remedies of creditors and the
effect of general principles of equity, whether enforcement is considered in a
proceeding in equity or at law, and the discretion of the court before which any
proceeding therefor may be brought. Payor hereby covenants and agrees to provide
Payee with copies of its required periodic reports filed with the Securities and
Exchange Commission within a reasonable time following such filings.

      7.10 Action by Payee. Subject to the provisions of this Section 7.10, the
Payee and Payor may enter into agreements for the purpose of adding or modifying
provisions of the Subordinated Note or changing in any manner the rights of the
Payee or Payor hereunder or waiving any covenant, default or Event of Default
hereunder; provided, however, that no change may be made to this Note which
would either modify the subordination provisions hereof or would otherwise
adversely affect the rights of the holders of Senior Debt without the written
consent, prior to the indefeasible repayment thereof in full in cash, of the
Agent.

            IN WITNESS WHEREOF, Payor has executed and delivered this Note as of
the date hereinabove first written.


                                    FEDERAL DATA CORPORATION


                                    By:   /s/ James Dean
                                    Name: James Dean
                                    Title: Vice President and Chief
                                           Financial Officer


                                       15
<PAGE>

                                 Acknowledgment

            Ralph O. Williams, Payee under the attached 9% Subordinated
Promissory Note, dated as of February 17, 1998 (the "Note") hereby acknowledges
the provisions of Section 4, Section 5 and Section 7.10 of the Note and agrees
to be bound by the provisions thereof.


By: /s/ Ralph O. Williams
Name:  Ralph O. Williams



STATE OF
                                       ss:
COUNTY OF _____________________

           On this 17th day of February, 1998, before me personally came Ralph
O. Williams to be known and known to me to be the individual described in and
who executed the foregoing Acknowledgment and acknowledged to me that he
executed the same.


Signed and sworn before me                SEAL
on February __, 1998

___________________________               My commission expires:
Notary Public

574477


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