Document:

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                                                                Exhibit 4.2

                         REGISTRATION RIGHTS AGREEMENT

                                  June 4, 1998

To each of the several Purchasers named in Schedule I to the Series A
Convertible Preferred Stock Purchase Agreement of even date herewith (the
"Purchasers"), Anchor Financial Group LLC ("Anchor"), the holders of the
-----------
Warrants to Purchase Common Stock (the "Bridge Warrants") issued pursuant to the
                                        ---------------
Bridge Financing Agreement dated February 16, 1998 (the "Bridge Warrant
                                                                -------
Holders"), Douglas E. Humphrey and Lisa Losito (the "Founders").
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Ladies and Gentlemen:

     This will confirm that in consideration of the Purchasers' agreement on the
date hereof to purchase an aggregate of 7,066,147 shares of Series A Convertible
Preferred Stock, $.01 par value ("Preferred Stock"), of SkyCache, Inc., a
                                  ---------------
Delaware corporation (the "Company"), pursuant to the Series A Convertible
                           -------
Preferred Stock Purchase Agreement of even date herewith (the "Purchase
                                                               --------
Agreement") between the Company and the Purchasers and as an inducement to the
---------
Purchasers to consummate the transactions contemplated by the Purchase Agreement
and in consideration of the waiver by the Bridge Warrant Holders of their
registration rights, their anti-dilution rights and their rights of first
refusal contained in sections 8 and 10, respectively, of the Bridge Warrants and
in consideration for the prior dedication and effort of the Founders, the
Company covenants and agrees with each of you as follows:

     1.  Certain Definitions.  As used in this Agreement, the following terms
         -------------------
shall have the following respective meanings:

     "Commission" shall mean the Securities and Exchange Commission, or any
      ----------
   other federal agency at the time administering the Securities Act.

     "Common Stock" shall mean the Common Stock, $.01 par value, of the Company,
      ------------
   as constituted as of the date of this Agreement.

     "Conversion Shares" shall mean shares of Common Stock issued upon
      -----------------
   conversion of the Preferred Shares and shares of Common Stock issued or
   issuable upon conversion of any shares of preferred stock of any series
   hereafter acquired by Purchasers.

     "Exchange Act" shall mean the Securities Exchange Act of 1934, as amended,
      ------------
   or any similar federal statute, and the rules and regulations of the
   Commission thereunder, all as the same shall be in effect at the time.

     "Founders' Stock" shall mean the shares of Common Stock held by the
      ---------------
   Founders.
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                    Registration Rights Agreement -- Page 2

     "Preferred Shares" shall mean the shares of Preferred Stock purchased by
      ----------------
   the Purchasers on the date hereof and the shares of Preferred Stock issued
   upon the exercise of warrants issued to Anchor or its designees, pursuant to
   that certain letter agreement dated as of February 10, 1998 by and among the
   Company and Anchor.

     "Registration Expenses" shall mean the expenses so described in Section 8.
      ---------------------

     "Restricted Stock" shall mean the Conversion Shares and any other shares of
      ----------------
   Common Stock hereafter acquired by Purchasers, excluding any such Conversion
   Shares or shares of Common Stock which have been (a) registered under the
   Securities Act pursuant to an effective registration statement filed
   thereunder and disposed of in accordance with the registration statement
   covering them or (b) publicly sold pursuant to Rule 144 under the Securities
   Act.

     "Securities Act" shall mean the Securities Act of 1933, as amended, or any
      --------------
   similar federal statute, and the rules and regulations of the Commission
   thereunder, all as the same shall be in effect at the time.

     "Selling Expenses" shall mean the expenses so described in Section 8.
      ----------------

     "Warrant Shares" shall mean the shares of Common Stock issued upon exercise
      --------------
   of the Bridge Warrants.

          2.  Restrictive Legend. Each certificate representing Preferred
              ------------------
Shares, Warrant Shares or Conversion Shares shall, except as otherwise provided
in this Section 2 or in Section 3, be stamped or otherwise imprinted with a
legend substantially in the following form:

          "THIS SECURITY HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF
       1933 OR ANY STATE SECURITIES LAWS AND MAY NOT BE TRANSFERRED OR OTHERWISE
       DISPOSED OF UNLESS IT HAS BEEN REGISTERED UNDER SUCH ACT AND ALL SUCH
       APPLICABLE LAWS OR AN EXEMPTION FROM REGISTRATION IS AVAILABLE."

A certificate shall not bear such legend if in the opinion of counsel
satisfactory to the Company (it being agreed that Testa, Hurwitz & Thibeault,
LLP shall be satisfactory) the securities represented thereby may be publicly
sold without registration under the Securities Act and any applicable state
securities laws.

          3. Notice of Proposed Transfer. Prior to any proposed transfer of any
             ---------------------------
Preferred Shares, Warrant Shares or Conversion Shares (other than under the
circumstances described in Sections 4, 5 or 6), the holder thereof shall give
written notice to the Company of its intention to effect such transfer. Each
such notice shall describe the manner of the proposed transfer and, if requested
by the Company, shall be accompanied by an opinion of counsel satisfactory to

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                    Registration Rights Agreement -- Page 3

the Company (it being agreed that Testa, Hurwitz & Thibeault, LLP shall be
satisfactory) to the effect that the proposed transfer may be effected without
registration under the Securities Act and any applicable state securities laws,
whereupon the holder of such stock shall be entitled to transfer such stock in
accordance with the terms of its notice; provided, however, that no such opinion
                                         --------  -------
of counsel shall be required for a transfer to one or more partners or members
of the transferor (in the case of a transferor that is a partnership or a
limited liability company, respectively) or to an affiliated corporation (in the
case of a transferor that is a corporation). Each certificate for Preferred
Shares, Warrant Shares or Conversion Shares transferred as above provided shall
bear the legend set forth in Section 2, except that such certificate shall not
bear such legend if (i) such transfer is in accordance with the provisions of
Rule 144 (or any other rule permitting public sale without registration under
the Securities Act) or (ii) the opinion of counsel referred to above is to the
further effect that the transferee and any subsequent transferee (other than an
affiliate of the Company) would be entitled to transfer such securities in a
public sale without registration under the Securities Act. The restrictions
provided for in this Section 3 shall not apply to securities which are not
required to bear the legend prescribed by Section 2 in accordance with the
provisions of that Section.

          4.  Required Registration. (a) At any time after the earlier of (i)
              ---------------------
the effective date of any registration statement covering a public offering of
securities of the Company under the Securities Act and (ii) the third
anniversary of the date of this Agreement, the holders of Restricted Stock
constituting at least 50% of the total shares of Restricted Stock then
outstanding may request the Company to register under the Securities Act all or
any portion of the shares of Restricted Stock held by such requesting holder or
holders for sale in the manner specified in such notice, provided that the
                                                         --------
shares of Restricted Stock for which registration has been requested shall (i)
constitute at least 20% of the total shares of Restricted Stock originally
issued if such holder or holders shall request the registration of less than all
shares of Restricted Stock then held by such holder or holders; and (ii) have an
anticipated aggregate public offering price of not less than $5 million.  For
purposes of this Section 4 and Sections 5, 6, 13(a) and 13(d), the term
"Restricted Stock" shall be deemed to include the number of shares of Restricted
Stock which would be issuable to a holder of Preferred Shares upon conversion of
all Preferred Shares and any other shares of preferred stock of any series
hereafter acquired held by such holder at such time, provided, however, that the
                                                     --------  -------
only securities which the Company shall be required to register pursuant hereto
shall be shares of Common Stock, and provided, further, however, that, in any
                                     --------  -------  -------
underwritten public offering contemplated by this Section 4 or Sections 5 and 6,
the holders of Preferred Shares shall be entitled to sell such Preferred Shares
and any other shares of preferred stock of any series hereafter acquired to the
underwriters for conversion and sale of the shares of Common Stock issued upon
conversion thereof.  Notwithstanding anything to the contrary contained herein,
no request may be made under this Section 4 within 180 days after the effective
date of a registration statement filed by the Company covering a firm commitment
underwritten public offering in which the holders of Restricted Stock shall have
been entitled to join pursuant to Sections 5 or 6 and in which there shall have
been effectively registered all shares of Restricted Stock as to which
registration shall have been requested.

          (b)  Following receipt of any notice under this Section 4, the Company
shall immediately notify all holders of Restricted Stock from whom notice has
not been received and shall use its best efforts to register under the

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                    Registration Rights Agreement -- Page 4

Securities Act, for public sale in accordance with the method of disposition
specified in such notice from requesting holders, the number of shares of
Restricted Stock specified in such notice (and in all notices received by the
Company from other holders within 30 days after the giving of such notice by the
Company). If such method of disposition shall be an underwritten public
offering, the Company may designate the managing underwriter of such offering,
subject to the approval of the holders of a majority of the shares of Restricted
Stock to be sold in such offering, which approval shall not be unreasonably
withheld or delayed. The Company shall be obligated to register Restricted Stock
pursuant to this Section 4 on two occasions only, provided, however, that such
                                                  --------  -------
obligation shall be deemed satisfied only when a registration statement covering
all shares of Restricted Stock specified in notices received as aforesaid, for
sale in accordance with the method of disposition specified by the requesting
holders, shall have become effective and, if such method of disposition is a
firm commitment underwritten public offering, all such shares shall have been
sold pursuant thereto.

          (c) The Company shall be entitled to include in any registration
statement referred to in this Section 4, for sale in accordance with the method
of disposition specified by the requesting holders, shares of Common Stock to be
sold by the Company for its own account, except as and to the extent that, in
the opinion of the managing underwriter (if such method of disposition shall be
an underwritten public offering), such inclusion would adversely affect the
marketing of the Restricted Stock to be sold. Except for registration statements
on Form S-4, S-8 or any successor thereto, the Company will not file with the
Commission any other registration statement with respect to its Common Stock,
whether for its own account or that of other stockholders, from the date of
receipt of a notice from requesting holders pursuant to this Section 4 until the
completion of the period of distribution of the registration contemplated
thereby.

          (d)  Notwithstanding any other provision of this Section 4, if the
                                                           ---------
underwriter(s) advise(s) the Company in writing that marketing factors require a
limitation of the number of securities to be underwritten then the Company shall
so advise all holders of Restricted Stock which would otherwise be registered
and underwritten pursuant hereto, and the number of shares of Restricted Stock
that may be included in the underwriting shall be reduced as required by the
underwriter(s) and allocated among the holders of Restricted Stock on a pro rata
basis according to the number of shares of Restricted Stock then outstanding
held by each holder requesting registration; provided, however, that the number
                                             --------  -------
of shares of Restricted Stock to be included in such underwriting and
registration shall not be reduced unless all other securities of the Company are
first entirely excluded from the underwriting and registration.  Any shares of
Restricted Stock excluded and withdrawn from such underwriting shall be
withdrawn from the registration.

          (e) Notwithstanding the foregoing, if the Company shall furnish to
holders requesting the filing of a registration statement pursuant to this
Section 4, a certificate signed by the President or Chief Executive Officer
---------
of the Company stating that in the good faith judgment of the Board of Directors
of the Company, it would be seriously detrimental to the Company and its
stockholders for such registration statement to be filed and it is therefore
essential to defer the filing of such registration statement, then the Company
shall have the right to defer such filing for a period of not more than 120 days
after receipt of the request of the holders; provided, however, that the Company
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                    Registration Rights Agreement -- Page 5

may notutilize this right more than once in any twelve (12) month period.

          5.  Incidental Registration.  If the Company at any time (other than
              -----------------------
pursuant to Section 4 or Section 6) proposes to register any of its securities
under the Securities Act for sale to the public, whether for its own account or
for the account of other security holders or both (except with respect to
registration statements on Forms S-4, S-8 or another form not available for
registering the Restricted Stock, the Warrant Shares or the Founders' Stock for
sale to the public), each such time it will give written notice to all holders
of outstanding Restricted Stock, Warrant Shares or Founders' Stock of its
intention so to do.  Upon the written request of any such holder, received by
the Company within 30 days after the giving of any such notice by the Company,
to register any of its Restricted Stock, Warrant Shares or Founders' Stock, the
Company will use its best efforts to cause the Restricted Stock, Warrant Shares
or Founders' Stock as to which registration shall have been so requested to be
included in the securities to be covered by the registration statement proposed
to be filed by the Company, all to the extent requisite to permit the sale or
other disposition by the holder of such Restricted Stock, Warrant Shares or
Founders' Stock so registered.  In the event that any registration pursuant to
this Section 5 shall be, in whole or in part, an underwritten public offering of
Common Stock, the number of shares of Restricted Stock, Warrant Shares or
Founders' Stock to be included in such an underwriting may be reduced (pro rata
among the requesting holders based upon the number of shares of Restricted
Stock, Warrant Shares or Founders' Stock owned by such holders) if and to the
extent that the managing underwriter shall be of the opinion that such inclusion
would adversely affect the marketing of the securities to be sold by the Company
therein, provided, however, that such number of shares of Restricted Stock,
         --------  -------
Warrant Shares or Founders' Stock shall not be reduced if any shares are to be
included in such underwriting for the account of any person other than the
Company or requesting holders of Restricted Stock, Warrant Shares or Founders'
Stock, and provided, further, however, that in no event may less than one-third
           --------  -------  -------
of the total number of shares of Common Stock to be included in such
underwriting be made available for shares of Restricted Stock or Founders' Stock
except in the event that the underwritten offering is the initial public
offering of the Company in which case all of the Restricted Stock, Warrant
Shares and Founders' Stock may be excluded.  Notwithstanding the foregoing
provisions, the Company may withdraw any registration statement referred to in
this Section 5 without thereby incurring any liability to the holders of
Restricted Stock, Warrant Shares or Founders' Stock.

          6. Registration on Form S-3. If at any time (i) a holder or holders of
             ------------------------
at least 50% of the Preferred Shares or Restricted Stock request that the
Company file a registration statement on Form S-3 or any successor thereto for a
public offering of all or any portion of the shares of Restricted Stock held by
such requesting holder or holders, the reasonably anticipated aggregate price to
the public of which would exceed $1,000,000, and (ii) the Company is a
registrant entitled to use Form S-3 or any successor thereto to register such
shares, then the Company shall use its best efforts to register under the
Securities Act on Form S-3 or any successor thereto, for public sale in
accordance with the method of disposition specified in such notice, the number
of shares of Restricted Stock specified in such notice. Whenever the Company is
required by this Section 6 to use its best efforts to effect the registration of
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                    Registration Rights Agreement -- Page 6

Restricted Stock, each of the procedures and requirements of Section 4
(including but not limited to the requirement that the Company notify all
holders of Restricted Stock from whom notice has not been received and provide
them with the opportunity to participate in the offering) shall apply to such
registration, provided, however, that the Company shall not be obligated to
              --------  -------
effect more than one such registration in any twelve month period on Form S-3
under this Section 6, and provided, further, however, that the requirements
                          --------  -------  -------
contained in the first sentence of Section 4(a) shall not apply to any
registration on Form S-3 which may be requested and obtained under this Section
6.

          7.  Registration Procedures. If and whenever the Company is required
              -----------------------
by the provisions of Sections 4, 5 or 6 to use its best efforts to effect the
registration of any shares of Restricted Stock, Warrant Shares or Founders'
Stock under the Securities Act, the Company will, as expeditiously as possible:

          (a) prepare and file with the Commission a registration statement
(which, in the case of an underwritten public offering pursuant to Section 4,
shall be on Form S-1 or other form of general applicability satisfactory to the
managing underwriter selected as therein provided) with respect to such
securities and use its best efforts to cause such registration statement to
become and remain effective for the period of the distribution contemplated
thereby (determined as hereinafter provided);

          (b) prepare and file with the Commission such amendments and
supplements to such registration statement and the prospectus used in connection
therewith as may be necessary to keep such registration statement effective for
the period specified in paragraph (a) above and comply with the provisions of
the Securities Act with respect to the disposition of all Restricted Stock,
Warrant Shares or Founders' Stock covered by such registration statement in
accordance with the sellers' intended method of disposition set forth in such
registration statement for such period;

          (c)  furnish to each seller of Restricted Stock, Warrant Shares or
Founders' Stock and to each underwriter such number of copies of the
registration statement and the prospectus included therein (including each
preliminary prospectus) as such persons reasonably may request in order to
facilitate the public sale or other disposition of the Restricted Stock, Warrant
Shares or Founders' Stock covered by such registration statement;

          (d)  use its best efforts to register or qualify the Restricted Stock,
Warrant Shares or Founders' Stock covered by such registration statement under
the securities or "blue sky" laws of such jurisdictions as the sellers of
Restricted Stock, Warrant Shares or Founders' Stock or, in the case of an
underwritten public offering, the managing underwriter reasonably shall request,

provided, however, that the Company shall not for any such purpose be required
--------  -------
to qualify generally to transact business as a foreign corporation in any
jurisdiction where it is not so qualified or to consent to general service of
process in any such jurisdiction;

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                    Registration Rights Agreement -- Page 7

          (e) use its best efforts to list the Restricted Stock, Warrant Shares
or Founders' Stock covered by such registration statement with any securities
exchange on which the Common Stock of the Company is then listed;

          (f) immediately notify each seller of Restricted Stock, Warrant Shares
or Founders' Stock and each underwriter under such registration statement, at
any time when a prospectus relating thereto is required to be delivered under
the Securities Act, of the happening of any event of which the Company has
knowledge as a result of which the prospectus contained in such registration
statement, as then in effect, includes an untrue statement of a material fact or
omits to state a material fact required to be stated therein or necessary to
make the statements therein not misleading in light of the circumstances then
existing;

          (g) if the offering is underwritten and at the request of any seller
of Restricted Stock, Warrant Shares or Founders' Stock, use its best efforts to
furnish on the date that Restricted Stock or Founders' Stock is delivered to the
underwriters for sale pursuant to such registration: (i) an opinion dated such
date of counsel representing the Company for the purposes of such registration,
addressed to the underwriters and to such seller, stating that such registration
statement has become effective under the Securities Act and that (A) to the best
knowledge of such counsel, no stop order suspending the effectiveness thereof
has been issued and no proceedings for that purpose have been instituted or are
pending or contemplated under the Securities Act, (B) the registration
statement, the related prospectus and each amendment or supplement thereof
comply as to form in all material respects with the requirements of the
Securities Act (except that such counsel need not express any opinion as to
financial statements contained therein) and (C) to such other effects as
reasonably may be requested by counsel for the underwriters or by such seller or
its counsel and (ii) a letter dated such date from the independent public
accountants retained by the Company, addressed to the underwriters and to such
seller, stating that they are independent public accountants within the meaning
of the Securities Act and that, in the opinion of such accountants, the
financial statements of the Company included in the registration statement or
the prospectus, or any amendment or supplement thereof, comply as to form in all
material respects with the applicable accounting requirements of the Securities
Act, and such letter shall additionally cover such other financial matters
(including information as to the period ending no more than five business days
prior to the date of such letter) with respect to such registration as such
underwriters reasonably may request; and

          (h) make available for inspection by each seller of Restricted Stock,
Warrant Shares or Founders' Stock, any underwriter participating in any
distribution pursuant to such registration statement, and any attorney,
accountant or other agent retained by such seller or underwriter, all financial
and other records, pertinent corporate documents and properties of the Company,
and cause the Company's officers, directors and employees to supply all
information reasonably requested by any such seller, underwriter, attorney,
accountant or agent in connection with such registration statement.

          For purposes of Section 7(a) and 7(b) and of Section 4(c), the period
of distribution of Restricted Stock in a firm commitment underwritten public
offering shall be deemed to extend until each underwriter has completed the
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                    Registration Rights Agreement -- Page 8

distribution of all securities purchased by it, and the period of distribution
of Restricted Stock in any other registration shall be deemed to extend until
the earlier of the sale of all Restricted Stock covered thereby and 120 days
after the effective date thereof.

          In connection with each registration hereunder, the sellers of
Restricted Stock, Warrant Shares or Founders' Stock will furnish to the Company
in writing such information with respect to themselves and the proposed
distribution by them as reasonably shall be necessary in order to assure
compliance with federal and applicable state securities laws.

          In connection with each registration pursuant to Sections 4, 5 or 6
covering an underwritten public offering, the Company and each seller agree to
enter into a written agreement with the managing underwriter selected in the
manner herein provided in such form and containing such provisions as are
customary in the securities business for such an arrangement between such
underwriter and companies of the Company's size and investment stature.

          8.  Expenses.  All expenses incurred by the Company in complying with
              --------
Sections 4, 5 and 6, including, without limitation, all registration and filing
fees, printing expenses, fees and disbursements of counsel and independent
public accountants for the Company, fees and expenses (including counsel fees)
incurred in connection with complying with state securities or "blue sky" laws,
fees of the National Association of Securities Dealers, Inc., transfer taxes,
fees of transfer agents and registrars, costs of insurance and fees and
disbursements of one counsel for the sellers of Restricted Stock, Warrant Shares
and Founders' Stock, but excluding any Selling Expenses, are called
"Registration Expenses".  All underwriting discounts and selling commissions
applicable to the sale of Restricted Stock, Warrant Shares and Founders' Stock
are called "Selling Expenses".

          The Company will pay all Registration Expenses in connection with each
registration statement under Sections 4, 5 or 6.  All Selling Expenses in
connection with each registration statement under Sections 4, 5 or 6 shall be
borne by the participating sellers in proportion to the number of shares sold by
each, or by such participating sellers other than the Company (except to the
extent the Company shall be a seller) as they may agree.

          9. Indemnification and Contribution. (a) In the event of a
             --------------------------------
registration of any of the Restricted Stock, Warrant Shares or Founders' Stock
under the Securities Act pursuant to Sections 4, 5 or 6, the Company will
indemnify and hold harmless each seller of such Restricted Stock, Warrant Shares
or Founders' Stock thereunder, each underwriter of such Restricted Stock,
Warrant Shares or Founders' Stock thereunder and each other person, if any, who
controls such seller or underwriter within the meaning of the Securities Act,
against any losses, claims, damages or liabilities, joint or several, to which
such seller, underwriter or controlling person may become subject under the
Securities Act or otherwise, insofar as such losses, claims, damages or
liabilities (or actions in respect thereof) arise out of or are based upon any
untrue statement or alleged untrue statement of any material fact contained in
any registration statement under which such Restricted Stock, Warrant Shares or
Founders' Stock was registered under the Securities Act pursuant to Sections 4,
5 or 6, any preliminary prospectus or final prospectus contained therein, or any
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                    Registration Rights Agreement -- Page 9

amendment or supplement thereof, or arise out of or are based upon the omission
or alleged omission to state therein a material fact required to be stated
therein or necessary to make the statements therein not misleading, and will
reimburse each such seller, each such underwriter and each such controlling
person for any legal or other expenses reasonably incurred by them in connection
with investigating or defending any such loss, claim, damage, liability or
action, provided, however, that the Company will not be liable in any such case
        --------  -------
if and to the extent that any such loss, claim, damage or liability arises out
of or is based upon an untrue statement or alleged untrue statement or omission
or alleged omission so made in conformity with information furnished by any such
seller, any such underwriter or any such controlling person in writing
specifically for use in such registration statement or prospectus.

          (b)   In the event of a registration of any of the Restricted Stock,
Warrant Shares or Founders' Stock under the Securities Act pursuant to Sections
4, 5 or 6, each seller of such Restricted Stock, Warrant Shares or Founders'
Stock thereunder, severally and not jointly, will indemnify and hold harmless
the Company, each person, if any, who controls the Company within the meaning of
the Securities Act, each officer of the Company who signs the registration
statement, each director of the Company, each underwriter and each person who
controls any underwriter within the meaning of the Securities Act, against all
losses, claims, damages or liabilities, joint or several, to which the Company
or such officer, director, underwriter or controlling person may become subject
under the Securities Act or otherwise, insofar as such losses, claims, damages
or liabilities (or actions in respect thereof) arise out of or are based upon
any untrue statement or alleged untrue statement of any material fact contained
in the registration statement under which such Restricted Stock, Warrant Shares
or Founders' Stock was registered under the Securities Act pursuant to Sections
4, 5 or 6, any preliminary prospectus or final prospectus contained therein, or
any amendment or supplement thereof, or arise out of or are based upon the
omission or alleged omission to state therein a material fact required to be
stated therein or necessary to make the statements therein not misleading, and
will reimburse the Company and each such officer, director, underwriter and
controlling person for any legal or other expenses reasonably incurred by them
in connection with investigating or defending any such loss, claim, damage,
liability or action, provided, however, that such seller will be liable
                     --------  -------
hereunder in any such case if and only to the extent that any such loss, claim,
damage or liability arises out of or is based upon an untrue statement or
alleged untrue statement or omission or alleged omission made in reliance upon
and in conformity with information pertaining to such seller, as such, furnished
in writing to the Company by such seller specifically for use in such
registration statement or prospectus, and provided, further, however, that the
                                          --------  -------  -------
liability of each seller hereunder shall be limited to the proportion of any
such loss, claim, damage, liability or expense which is equal to the proportion
that the public offering price of the shares sold by such seller under such
registration statement bears to the total public offering price of all
securities sold thereunder, but not in any event to exceed the net proceeds
received by such seller from the sale of Restricted Stock, Warrant Shares or
Founders' Stock covered by such registration statement.

          (c)   Promptly after receipt by an indemnified party hereunder of
notice of the commencement of any action, such indemnified party shall, if a
claim in respect thereof is to be made against the indemnifying party hereunder,
notify the indemnifying party in writing thereof, but the omission so to notify
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                   Registration Rights Agreement -- Page 10

the indemnifying party shall not relieve it from any liability which it may have
to such indemnified party other than under this Section 9 and shall only relieve
it from any liability which it may have to such indemnified party under this
Section 9 if and to the extent the indemnifying party is prejudiced by such
omission. In case any such action shall be brought against any indemnified party
and it shall notify the indemnifying party of the commencement thereof, the
indemnifying party shall be entitled to participate in and, to the extent it
shall wish, to assume and undertake the defense thereof with counsel
satisfactory to such indemnified party, and, after notice from the indemnifying
party to such indemnified party of its election so to assume and undertake the
defense thereof, the indemnifying party shall not be liable to such indemnified
party under this Section 9 for any legal expenses subsequently incurred by such
indemnified party in connection with the defense thereof other than reasonable
costs of investigation and of liaison with counsel so selected, provided,
                                                                --------
however, that, if the defendants in any such action include both the
-------
indemnifiedparty and the indemnifying party and the indemnified party shall have
reasonably concluded that there may be reasonable defenses available to it which
are different from or additional to those available to the indemnifying party or
if the interests of the indemnified party reasonably may be deemed to conflict
with the interests of the indemnifying party, the indemnified party shall have
the right to select a separate counsel and to assume such legal defenses and
otherwise to participate in the defense of such action, with the expenses and
fees of such separate counsel and other expenses related to such participation
to be reimbursed by the indemnifying party as incurred.

          (d) In order to provide for just and equitable contribution to joint
liability under the Securities Act in any case in which either (i) any holder of
Restricted Stock, Warrant Shares or Founders' Stock exercising rights under this
Agreement, or any controlling person of any such holder, makes a claim for
indemnification pursuant to this Section 9 but it is judicially determined (by
the entry of a final judgment or decree by a court of competent jurisdiction and
the expiration of time to appeal or the denial of the last right of appeal) that
such indemnification may not be enforced in such case notwithstanding the fact
that this Section 9 provides for indemnification in such case, or (ii)
contribution under the Securities Act may be required on the part of any such
selling holder or any such controlling person in circumstances for which
indemnification is provided under this Section 9; then, and in each such case,
the Company and such holder will contribute to the aggregate losses, claims,
damages or liabilities to which they may be subject (after contribution from
others) in such proportion so that such holder is responsible for the portion
represented by the percentage that the public offering price of its Restricted
Stock, Warrant Shares or Founders' Stock offered by the registration statement
bears to the public offering price of all securities offered by such
registration statement, and the Company is responsible for the remaining
portion; provided, however, that, in any such case, (A) no such holder will be
         --------  -------
required to contribute any amount in excess of the public offering price of all
such Restricted Stock, Warrant Shares or Founders' Stock offered by it pursuant
to such registration statement; and (B) no person or entity guilty of fraudulent
misrepresentation (within the meaning of Section 11(f) of the Securities Act)
will be entitled to contribution from any person or entity who was not guilty of
such fraudulent misrepresentation.

          10.  Changes in Common Stock or Preferred Stock.  If, and as often as,
               ------------------------------------------
there is any change in the Common Stock or the Preferred Stock by way of a stock

<PAGE>

                   Registration Rights Agreement -- Page 11

split, stock dividend, combination or reclassification, or through a merger,
consolidation, reorganization or recapitalization, or by any other means,
appropriate adjustment shall be made in the provisions hereof so that the rights
and privileges granted hereby shall continue with respect to the Common Stock or
the Preferred Stock as so changed.

          11. Rule 144 Reporting. With a view to making available the benefits
              ------------------
of certain rules and regulations of the Commission which may at any time permit
the sale of the Restricted Stock, Warrant Shares or Founders' Stock to the
public without registration, at all times after 90 days after any registration
statement covering a public offering of securities of the Company under the
Securities Act shall have become effective, the Company agrees to:

          (a) make and keep public information available, as those terms are
understood and defined in Rule 144 under the Securities Act;

          (b) use its best efforts to file with the Commission in a timely
manner all reports and other documents required of the Company under the
Securities Act and the Exchange Act; and

          (c) furnish to each holder of Restricted Stock, Warrant Shares or
Founders' Stock forthwith upon request a written statement by the Company as to
its compliance with the reporting requirements of such Rule 144 and of the
Securities Act and the Exchange Act, a copy of the most recent annual or
quarterly report of the Company, and such other reports and documents so filed
by the Company as such holder may reasonably request in availing itself of any
rule or regulation of the Commission allowing such holder to sell any Restricted
Stock, Warrant Shares or Founders' Stock without registration.

          12. Representations and Warranties of the Company. The Company
              ---------------------------------------------
represents and warrants to you as follows:

          (a)  The execution, delivery and performance of this Agreement by the
Company have been duly authorized by all requisite corporate action and will not
violate any provision of law, any order of any court or other agency of
government, the Charter or By-laws of the Company or any provision of any
indenture, agreement or other instrument to which it or any or its properties or
assets is bound, conflict with, result in a breach of or constitute (with due
notice or lapse of time or both) a default under any such indenture, agreement
or other instrument or result in the creation or imposition of any lien, charge
or encumbrance of any nature whatsoever upon any of the properties or assets of
the Company.

          (b) This Agreement has been duly executed and delivered by the Company
and constitutes the legal, valid and binding obligation of the Company,
enforceable in accordance with its terms.

          13.  Miscellaneous.
               -------------

<PAGE>

                   Registration Rights Agreement -- Page 12

          (a) All covenants and agreements contained in this Agreement by or on
behalf of any of the parties hereto shall bind and inure to the benefit of the
respective successors and assigns of the parties hereto (including without
limitation transferees of any Preferred Shares, Bridge Warrants, Warrant Shares
or Restricted Stock), whether so expressed or not, provided, however, that
                                                   --------  -------
registration rights conferred herein on the holders of Preferred Shares, Bridge
Warrants, Warrant Shares or Restricted Stock shall only inure to the benefit of
a transferee of Preferred Shares, Bridge Warrants, Warrant Shares or Restricted
Stock if (i) there is transferred to such transferee at least 20% of the total
shares of Restricted Stock or Warrant Shares originally issued pursuant to the
Purchase Agreement or the Bridge Financing Agreement, respectively, to the
direct or indirect transferor of such transferee or (ii) such transferee is a
partner, shareholder or affiliate of a party hereto, and provided, further,
                                                         --------  -------
however, that no registration rights conferred herein to the Founders shall be
-------
transferable.

          (b) All notices, requests, consents and other communications hereunder
shall be in writing and shall be delivered in person, mailed by certified or
registered mail, return receipt requested, or sent by telecopier or telex,
addressed as follows:

     if to the Company or any Purchaser, at the address of such party set forth
   in the Purchase Agreement;

     if to any subsequent holder of Preferred Shares, Bridge Warrants, Warrant
   Shares or Restricted Stock, to it at such address as may have been furnished
   to the Company in writing by such holder;

     if to a Founder, at the address of the Company;

     if to a Bridge Warrant Holder, at the address of such party set forth in
   the Bridge Financing Agreement;

     if to Anchor, at 2445 M Street, Suite 490, Washington, DC  20037, attn:
   Robert McE. Stewart;

or, in any case, at such other address or addresses as shall have been furnished
in writing to the Company (in the case of a holder of Preferred Shares, Bridge
Warrants, Warrant Shares, Restricted Stock or Founders' Stock) or to the holders
of Preferred Shares, Bridge Warrants, Warrant Shares, Restricted Stock or
Founders' Stock (in the case of the Company) in accordance with the provisions
of this paragraph.

          (c) This Agreement shall be governed by and construed in accordance
with the laws of the State of Maryland, without giving effect to the principles
                                        ---------------------------------------
of conflicts of laws thereof.
----------------------------

          (d) This Agreement may not be amended or modified, and no provision
hereof may be waived, without the written consent of the Company and the holders
of at least two-thirds of the outstanding shares of Restricted Stock.

<PAGE>

                   Registration Rights Agreement -- Page 13

          (e) This Agreement may be executed in two or more counterparts, each
of which shall be deemed an original, but all of which together shall constitute
one and the same instrument.

          (f) The obligations of the Company to register shares of Restricted
Stock, Warrant Shares or Founders' Stock under Sections 4, 5 or 6 shall
terminate on the fifteenth anniversary of the date of this Agreement.

          (g) If requested in writing by the underwriters for the initial
underwritten public offering of securities of the Company, each holder of
Restricted Stock, Warrant Shares or Founders' Stock who is a party to this
Agreement shall agree not to sell publicly any shares of Restricted Stock,
Warrant Shares or Founders' Stock or any other shares of Common Stock
(other than shares of Restricted Stock or other shares of Common Stock being
registered in such offering), without the consent of such underwriters, for a
period of not more than 180 days following the effective date of the
registration statement relating to such offering; provided, however, that all
                                                  --------  -------
persons entitled toregistration rights with respect to shares of Common Stock
who are not parties to this Agreement, all other persons selling shares of
Common Stock in such offering, all persons holding in excess of 1% of the
capital stock of the Company on a fully diluted basis and all executive officers
and directors of the Company shall also have agreed not to sell publicly their
Common Stock under the circumstances and pursuant to the terms set forth in this
Section 13(g).

          (h) Notwithstanding the provisions of Section 7(a), the Company's
obligation to file a registration statement, or cause such registration
statement to become and remain effective, shall be suspended for a period not to
exceed 90 days in any 24-month period if there exists at the time material non-
public information relating to the Company which, in the reasonable opinion of
the Company, should not be disclosed.

          (i) The Company shall not grant to any third party any registration
rights more favorable than or inconsistent with any of those contained herein,
so long as any of the registration rights under this Agreement remains in
effect.

          (j) If any provision of this Agreement shall be held to be illegal,
invalid or unenforceable, such illegality, invalidity or unenforceability shall
attach only to such provision and shall not in any manner affect or render
illegal, invalid or unenforceable any other provision of this Agreement, and
this Agreement shall be carried out as if any such illegal, invalid or
unenforceable provision were not contained herein.
<PAGE>

                   Registration Rights Agreement -- Page 14

     Please indicate your acceptance of the foregoing by signing and returning
the enclosed counterpart of this letter, whereupon this Agreement shall be a
binding agreement between the Company and you.

                                     Very truly yours,

                                     SKYCACHE, INC.

                                       By:/s/ Douglas E. Humphrey
                                          -----------------------
                                          Douglas E. Humphrey
                                          President and Chief Executive Officer

AGREED TO AND ACCEPTED as of the date first above written.

Purchasers named in Schedule I  to the Purchase
Agreement:

CARLYLE VENTURE PARTNERS, L.P.

By: Its General Partner, TCG Ventures, Ltd.

By: /s/ J. Mitchell Reese
    ---------------------
        J. Mitchell Reese
        Attorney in Fact

C/S VENTURE INVESTORS, L.P.

By: Its General Partner, TCG Ventures, Ltd.

By: /s/ J. Mitchell Reese
    ---------------------
        J. Mitchell Reese
        Attorney in Fact

CARLYLE U.S. VENTURE PARTNERS, L.P.

By: Its General Partner, TCG Ventures, L.L.C.

By: /s/ J. Mitchell Reese
    ---------------------
        J. Mitchell Reese
        Managing Director
<PAGE>

                   Registration Rights Agreement -- Page 15

CARLYLE VENTURE COINVESTMENT, L.L.C.

By: Its Manager, TCG Ventures, L.L.C.

By: /s/ J. Mitchell Reese
   ----------------------
        J. Mitchell Reese
        Managing Director

BRIDGE WARRANT HOLDERS:

/s/ William R. Daniels
----------------------
William R. Daniels

/s/ Robert M. Dunham
--------------------
Robert M. Dunham

/s/ Clyde A. Heintzelman
------------------------
Clyde A. Heintzelman

/s/ Benjamin Maldonado
----------------------
Benjamin Maldonado

/s/ Robert M. Stewart
---------------------
Robert M. Stewart

<PAGE>

                   Registration Rights Agreement -- Page 16

/s/ William G. Stewart
----------------------
William G. Stewart

/s/ Thomas D. Washburne, Jr.
----------------------------
Thomas D. Washburne, Jr.

/s/ Lloyd W. Taylor
-------------------
Lloyd W. Taylor

BMW Partners

By:  /s/ William C. Trimble, III
     ---------------------------
         William C. Trimble, III
         General Partner

Rave Financial Services Inc.
----------------------------

By:  /s/ William Barrone
     -------------------
     William Barrone

Title:  Director of Finance
        -------------------

/s/ R. Douglas Rivers
---------------------
R. Douglas Rivers
<PAGE>

                   Registration Rights Agreement -- Page 17

FOUNDERS:

/s/ Douglas E. Humphrey
-----------------------
Douglas E. Humphrey

/s/ Lisa Losito
---------------
Lisa Losito
<PAGE>

                   Registration Rights Agreement -- Page 18

ANCHOR DESIGNEES:

/s/ Robert M. Stewart
---------------------
Robert M. Stewart

/s/ Stuart J. Yarbrough
-----------------------
Stuart J. Yarbrough

/s/ Edward J. Mathias
---------------------
Edward J. Mathias

Robert C. McCormack Trust 10/6/67

By:/s/ Robert C. McCormack
   -----------------------
Name:
Title:

SBR, Inc.

By:/s/ Sam Ross
   ------------
Name:
Title:

/s/ Harold W. Purcell
---------------------
Harold W. Purcell

/s/ Edward M. Rogers
--------------------
Edward M. Rogers

/s/ James M. Sutton
-------------------
James M. Sutton

/s/ Charles L. Dunlap
---------------------
Charles L. Dunlap

/s/ Pascal Luck
---------------
Pascal Luck<PAGE>

                                                                     Exhibit 4.3

                               AMENDMENT NO. 1 TO
                         REGISTRATION RIGHTS AGREEMENT

                                  June 9, 1999

To each of the Purchasers named in
Schedule I to the Series B Convertible
----------
Preferred Stock Purchase Agreement
dated June 9, 1999 (the "Purchasers")

Ladies and Gentlemen:

     On June 4, 1998 SkyCache, Inc., a Delaware corporation (the "Company"),
Douglas E. Humphrey, Lisa Losito, each of the several purchasers listed on

Schedule I to that certain Series A Convertible Preferred Stock Purchase
----------
Agreement of even date therewith, Anchor Financial Group LLC, and the holders of
the Warrants to Purchase shares of the Common Stock, $.01 par value, of the
Company issued pursuant to that certain Bridge Financing Agreement dated
February 16, 1998, entered into a Registration Rights Agreement (the
"Agreement") of even date therewith.  The parties to the Agreement now wish to
amend the Agreement to extend the rights and benefits thereof to holders of
Series B Convertible Preferred Stock, $.01 par value, of the Company (the
"Series B Preferred Stock") issued pursuant to that certain Series B Convertible
Preferred Stock Purchase Agreement of even date herewith (the "Series B Stock
Purchase Agreement") by and among the Company and the Purchasers and to make
certain other changes as hereinafter set forth.  In consideration of and
pursuant to the foregoing, the Company covenants and agrees with each of you
that the Agreement is hereby amended as follows:

        1.  All of the shares of Series B Preferred Stock purchased pursuant to
            the Series B Stock Purchase Agreement shall be "Preferred Shares"
            for all purposes and to the same extent as if they were originally
            included as "Preferred Shares" under the Agreement and all
            references in the Agreement to the "Preferred Stock" and the
            "Purchase Agreement" shall include all of the shares of such Series
            B Preferred Stock and the Series B Stock Purchase Agreement,
            respectively.
<PAGE>

        2.  The last sentence of Section 6 of the Agreement shall be deleted in
            its entirety and replaced with following:

          "Whenever the Company is required by this Section 6 to use its best
          efforts to effect the registration of Restricted Stock, each of the
          procedures and requirements of Section 4 (including but not limited to
          the requirement that the Company notify all holders of Restricted
          Stock from whom notice has not been received and provide them with the
          opportunity to participate in the offering) shall apply to such
          registration, provided, however, that the Company shall not be
                        --------  -------
          obligated to effect more than two such registrations in any twelve
          month period on Form S-3 under this Section 6, and provided, further,
                                                             --------  -------
          however, that the requirements contained in the first sentence of
          -------
          Section 4(a) shall not apply to any registration on Form S-3 which may
          be requested and obtained under this Section 6."

     This Amendment may be executed in two or more counterparts, each of which
shall be deemed an original, but all of which together shall constitute one and
the same instrument.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]
<PAGE>

     Please indicate your acceptance of the foregoing by signing and returning
the enclosed counterpart of this letter, whereupon this Agreement shall be a
binding agreement between the Company and you.

                                     Very truly yours,

                                     SKYCACHE, INC.

                                             By:  /s/ Douglas E. Humphrey
                                                  -----------------------
                                                  Douglas E. Humphrey
                                                  President and Chief Executive
                                                  Officer

AGREED TO AND ACCEPTED as of the
date first above written.

CARLYLE VENTURE PARTNERS, L.P.

By: Its General Partner, TCG Ventures, Ltd.

By:/s/ J. Mitchell Reese
   ------------------------
        J. Mitchell Reese
        Attorney in Fact

C/S VENTURE INVESTORS, L.P.

By: Its General Partner, TCG Ventures, Ltd.

By: /s/ J. Mitchell Reese
   -------------------------
        J. Mitchell Reese
        Attorney in Fact

CARLYLE U.S. VENTURE PARTNERS, L.P.

By: Its General Partner, TCG Ventures, L.L.C.

By: /s/ J. Mitchell Reese
   -------------------------
        J. Mitchell Reese
        Managing Director
<PAGE>

CARLYLE VENTURE COINVESTMENT, L.L.C.

By: Its Manager, TCG Ventures, L.L.C.

By: /s/ J. Mitchell Reese
   -------------------------
        J. Mitchell Reese
        Managing Director
<PAGE>

PURCHASERS NOT PREVIOUSLY
PARTY TO THE AGREEMENT

NEW ENTERPRISE ASSOCIATES VIII,
LIMITED PARTNERSHIP

By:  NEA Partners VIII, Limited Partnership
     General Partner

     By: /s/ Nancy Dorman
         -----------------
         General Partner

NEA PRESIDENTS' FUND, L.P.

By:  NEA General Partners, L.P.
     General Partner

     By:/s/ Nancy Dorman
        ----------------
        General Partner

NEA VENTURES 1999, L.P.

     By:/s/ Nancy Dorman
        ----------------
        Vice President
         --------------

/s/ Frank A. Bonsal
-------------------
Frank A. Bonsal

/s/ John Landry
---------------
John Landry

/s/ Avram Miller, Trustee
-------------------------
The Avram Miller Trust

Intel Corporation

/s/ Arvind Sodhani
------------------
Arvid Sohani, Vice President and Treasurer
<PAGE>

Institutional Venture Partners, VIII, L.P.
By: its General Partner, Institutional Venture Management VIII, LLC

By:  /s/ R. Thomas Dyal
     ------------------
     R. Thomas, Dyal, Managing Director

IVM Investment Management Fund VIII, LLC,
By: its Manager Institutional Venture Management VIII, LLC

By:  /s/ R. Thomas Dyal
     ------------------
     R. Thomas, Dyal, Managing Director

IVP Broadband Fund, L.P.,
By: its General Partner IVP Broadband Management, LLC,
By: its Managing Director, Institutional Venture management VIII, LLC

By:  /s/ R. Thomas Dyal
     ------------------
     R. Thomas, Dyal, Managing Director
<PAGE>

Series B Purchaser

/s/ Thomas Washburne
--------------------
Thomas Washburne

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