PROSPECTUS
- -------------
 
                                 231,900 SHARES
 
                              INFORMIX CORPORATION
 
                                  COMMON STOCK
                               ($0.01 PAR VALUE)
 
    This  Prospectus  relates  to  the  public  offering,  which  is  not  being
underwritten, of shares of the common stock, $0.01 par value per share  ("Common
Stock"),  of Informix Corporation (together  with its consolidated subsidiaries,
"Informix") offered from time to time by any or all of the Selling  Stockholders
named  herein (the "Selling Stockholders") who  received such shares in exchange
for their shares of the capital stock of Stanford Technology Group, Inc. ("STG")
upon the merger of STG  with and into a  wholly-owned subsidiary of Informix  on
October  31, 1995.  Such shares  were issued pursuant  to an  exemption from the
registration requirements  of  the  Securities  Act of  1933,  as  amended  (the
"Securities  Act"), provided by  Section 4(2) thereof.  Informix will receive no
part of  the proceeds  of sales  made hereunder.  All expenses  of  registration
incurred  in connection with this offering are  being borne by Informix, but all
selling and other  expenses incurred by  Selling Stockholders will  be borne  by
such  Selling  Stockholders.  None  of  the  shares  offered  pursuant  to  this
Prospectus has been registered prior to the filing of the Registration Statement
of which this Prospectus is a part.
 
    The Common Stock offered hereby may be offered and sold from time to time by
the Selling Stockholders directly or through broker-dealers or underwriters  who
may act solely as agents, or who may acquire the Common Stock as principals. The
distribution  of the Common  Stock may be  effected in one  or more transactions
that may take place through the  Nasdaq National Market, including block  trades
or ordinary broker's transactions, or through privately negotiated transactions,
or  through underwritten public offerings, or  through a combination of any such
methods of sale,  at market prices  prevailing at  the time of  sale, at  prices
related  to such  prevailing market  prices or  at negotiated  prices. Usual and
customary or specially negotiated brokerage fees  or commissions may be paid  by
the   Selling  Stockholders  in  connection  with   such  sales.  See  "Plan  of
Distribution."
 
    The Common Stock of Informix is traded in the over-the-counter market on the
Nasdaq National Market (Nasdaq Symbol: IFMX).  On February 5, 1996, the  closing
sale price of a share of Informix's Common Stock was $30.63.
 
    SEE "RISK FACTORS" ON PAGE 3 FOR A DISCUSSION OF CERTAIN FACTORS THAT SHOULD
BE CONSIDERED BY PROSPECTIVE PURCHASERS OF THE COMMON STOCK OFFERED HEREBY.
 
    Each  Selling Stockholder and any broker  executing selling orders on behalf
of the Selling  Stockholders may  be deemed to  be an  "underwriter" within  the
meaning  of the Securities Act.  Commissions received by any  such broker may be
deemed to be underwriting commissions under the Securities Act.
 
                            ------------------------
 
    NO  PERSON  IS  AUTHORIZED   TO  GIVE  ANY  INFORMATION   OR  TO  MAKE   ANY
REPRESENTATIONS,  OTHER THAN THOSE  CONTAINED IN THIS  PROSPECTUS, IN CONNECTION
WITH THE OFFERING DESCRIBED HEREIN, AND,  IF GIVEN OR MADE, SUCH INFORMATION  OR
REPRESENTATIONS  MUST NOT BE RELIED UPON  AS HAVING BEEN AUTHORIZED BY INFORMIX.
THIS PROSPECTUS DOES NOT CONSTITUTE  AN OFFER TO SELL,  OR A SOLICITATION OF  AN
OFFER  TO BUY, NOR SHALL THERE BE ANY  SALE OF THESE SECURITIES BY ANY PERSON IN
ANY JURISDICTION IN WHICH  IT IS UNLAWFUL  FOR SUCH PERSON  TO MAKE SUCH  OFFER,
SOLICITATION  OR SALE. NEITHER THE DELIVERY OF THIS PROSPECTUS NOR ANY SALE MADE
HEREUNDER  SHALL  UNDER  ANY  CIRCUMSTANCES  CREATE  AN  IMPLICATION  THAT   THE
INFORMATION  CONTAINED HEREIN IS CORRECT  AS OF ANY TIME  SUBSEQUENT TO THE DATE
HEREOF.
 
                            ------------------------
 
    THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES AND
EXCHANGE COMMISSION OR ANY  STATE SECURITIES COMMISSION  NOR HAS THE  SECURITIES
AND  EXCHANGE  COMMISSION OR  ANY STATE  SECURITIES  COMMISSION PASSED  UPON THE
ACCURACY OR ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A
CRIMINAL OFFENSE.
 
                The date of this Prospectus is February 7, 1996.

                             AVAILABLE INFORMATION
 
    Informix is  subject  to the  informational  reporting requirements  of  the
Securities  Exchange  Act  of 1934,  as  amended  (the "Exchange  Act"),  and in
accordance therewith files reports, proxy statements and other information  with
the  Securities and Exchange Commission  (the "Commission"). Such reports, proxy
statements and  other information  can be  inspected and  copied at  the  Public
Reference Room of the Commission, 450 Fifth Street, N.W., Washington, D.C. 20549
and at the Commission's regional offices at: Seven World Trade Center, New York,
New  York  10048; and  500 West  Madison Street,  Suite 1400,  Chicago, Illinois
60661; and copies  of such material  can be obtained  form the Public  Reference
Section  of  the  Commission,  Washington,  D.C.  20549,  at  prescribed  rates.
Information  as  of  particular  dates  concerning  directors  and  officers  of
Informix,  their remuneration, options granted to them, the principal holders of
securities  of  Informix,  and  any   material  interest  of  such  persons   in
transactions with Informix has been or will be disclosed in the proxy statements
to be distributed to stockholders of Informix and filed with the Commission.
 
    This  Prospectus  contains  information concerning  Informix,  but  does not
contain all the information set forth in the Registration Statement on Form  S-3
which  Informix has filed with the  Securities and Exchange Commission under the
Securities Act  (the  "Registration  Statement").  The  Registration  Statement,
including  various  exhibits, may  be inspected  at  the Commission's  office in
Washington, D.C.
 
                     INFORMATION INCORPORATED BY REFERENCE
 
    There are hereby incorporated by reference in this Prospectus the  following
documents  and  information heretofore  filed with  the Securities  and Exchange
Commission:
 
    (1) Informix's Annual Report on Form 10-K for the fiscal year ended December
       31, 1994.
 
    (2) Informix's Quarterly Reports on Form 10-Q for the fiscal quarters  ended
       April 2, July 2, and October 1, 1995.
 
    (3)  Informix's Current Reports  on Form 8-K  filed on January  25, 1995 and
       Form 8-K/A filed on March 22, 1995.
 
    (4) Informix's Current Report on Form 8-K filed on February 7, 1996.
 
    (5) Informix's  Registration Statement  on Form  8-A/A filed  on August  11,
       1995.
 
    All  documents filed  by Informix  pursuant to  Section 13(a),  13(c), 14 or
15(d) of the Exchange  Act after the  date of this Prospectus  and prior to  the
termination of the offering of securities contemplated hereby shall be deemed to
be incorporated by reference in this Prospectus or any Prospectus Supplement and
to  be a part  hereof from the date  of filing of  such documents. Any statement
contained in a document incorporated by  reference or deemed to be  incorporated
by  reference in this Prospectus or any Prospectus Supplement shall be deemed to
be modified or superseded for all purposes of this Prospectus or such Prospectus
Supplement to the extent  that a statement contained  herein, therein or in  any
subsequently  filed  document  which  also  is  incorporated  or  deemed  to  be
incorporated by reference herein  or in such  Prospectus Supplement modifies  or
supersedes  such statement. Any  such statement so  modified or superseded shall
not be deemed, except as so modified or superseded, to constitute a part of this
Prospectus or any Prospectus Supplement.
 
    Informix will provide without charge to each  person to whom a copy of  this
Prospectus  has been delivered, upon the written or oral request of such person,
a copy of any and all of the documents referred to above which have been or  may
be  incorporated in  this Prospectus by  reference (other than  exhibits to such
documents, unless  such  exhibits  are specifically  incorporated  by  reference
therein).  Requests  for such  copies should  be  directed to:  General Counsel,
Informix  Corporation,  4100  Bohannon  Drive,  Menlo  Park,  California  94025;
telephone number (415) 926-6300.
 
                                       2

                                  THE COMPANY
 
    Informix  designs, develops, manufactures,  markets and supports distributed
relational   database   management   systems,   object-oriented,   graphical-and
character-based  application development  tools and  graphical data-access tools
for delivering information to most significant desktop platforms. In addition to
software products, Informix offers training,  consulting and maintenance to  its
customers.
 
    Informix  Corporation was initially  incorporated in California  in 1980 and
was reincorporated in Delaware in 1986. Informix maintains its executive offices
at 4100 Bohannon Drive, Menlo Park, California 94025 and its telephone number is
(415) 926-6300.
 
                          FORWARD LOOKING INFORMATION
 
    This Prospectus, including the information incorporated by reference herein,
contains forward-looking statements  within the  meaning of Section  27A of  the
Securities  Act and Section 21E of the Exchange Act. Actual results could differ
materially from those projected in the forward-looking statements as a result of
the risk  factors  set forth  below.  Reference is  made  in particular  to  the
discussion  set forth  under "Management's  Discussion of  Analysis of Financial
Condition and Results of Operations" in the  Annual Report on Form 10-K for  the
fiscal  year ended December 31,  1994 and in the  Quarterly Reports on Form 10-Q
for the fiscal quarters ended April 2, July 2 and October 1, 1995. In connection
with forward-looking statements which  appear in these disclosures,  prospective
purchasers  of  the  Common Stock  offered  hereby should  carefully  review the
factors set  forth  in this  Prospectus  under "Risk  Factors  --  Uncertainties
Relating  to the Merger with Illustra,"  "-- Fluctuations in Quarterly Results,"
"-- Volatility of  Informix Stock Prices,"  "-- Competition," "--  International
Operations" and "-- Management of Growth."
 
                                  RISK FACTORS
 
    In  addition to  the other  information in  this Prospectus  or incorporated
herein by reference,  the following  factors should be  considered carefully  in
evaluating  Informix and its business before purchasing the Common Stock offered
hereby:
 
    UNCERTAINTIES RELATING TO THE MERGER  WITH ILLUSTRA.  Informix and  Illustra
Information  Technologies, Inc. ("Illustra") have  entered into an Agreement and
Plan of Reorganization dated  as of December 20,  1995 (the "Merger  Agreement")
pursuant  to which  Illustra will  be merged  into a  wholly-owned subsidiary of
Informix ("Merger"). Illustra develops,  produces, markets and supports  object-
relational  database systems  and software  tools and  also provides consulting,
training and maintenance services.  As a result of  the Merger, all  outstanding
shares  of Illustra Common Stock and Illustra Preferred Stock will become shares
of Informix Common  Stock and all  outstanding options and  warrants to  acquire
Illustra  Common  Stock  or Illustra  Preferred  Stock will  become  options and
warrants to  acquire Informix  Common Stock.  The maximum  number of  shares  of
Informix  Common  Stock to  be  issued (including  Informix  Common Stock  to be
reserved for issuance upon exercise of any of Illustra's options and warrants to
be assumed by Informix) in the Merger in exchange for the outstanding shares  of
Illustra  Common  Stock  and  Illustra Preferred  Stock  and  all  unexpired and
unexercised options and warrants  to acquire Illustra  Common Stock or  Illustra
Preferred  Stock  will be  15,000,000.  The Merger  is  subject to  a  number of
conditions, including  approval  by  the  Illustra  stockholders.  Assuming  all
conditions  to  the Merger  are met  or  waived prior  thereto, it  is currently
anticipated that the effective time of the  Merger will be on or about  February
16, 1996. The following are risks associated with the Merger:
 
        UNCERTAINTIES  RELATING  TO  INTEGRATION OF  OPERATIONS.    Informix and
    Illustra have entered into  the Merger Agreement  with the expectation  that
    the  Merger will result in beneficial  synergies for the combined companies.
    Achieving the anticipated benefits  of the Merger will  depend in part  upon
    whether  the integration of the two  companies' businesses is achieved in an
    efficient and effective manner, and there can be no assurance that this will
    occur. The  combination  of the  two  companies will  require,  among  other
    things, integration of Illustra's object-relational database
 
                                       3

    technology with Informix's relational database technology and integration of
    their  respective sales and marketing  and research and development efforts.
    There can be no assurance that integration will be accomplished smoothly, on
    time or successfully. The difficulties of such integration may be  increased
    by  the complexity of the technologies being integrated and the necessity of
    coordinating geographically  separated  organizations.  The  integration  of
    certain  operations  following the  Merger  will require  the  dedication of
    management resources  which  may  temporarily distract  attention  from  the
    day-to-day  business  of  the  combined  companies.  Failure  to effectively
    accomplish the integration of  the two companies'  operations could have  an
    adverse effect on Informix's results of operations and financial condition.
 
        POTENTIAL  DILUTIVE  EFFECT  TO STOCKHOLDERS.    Although  the companies
    believe that beneficial synergies will result from the Merger, there can  be
    no  assurance that the  combining of the two  companies' businesses, even if
    achieved in  an  efficient, effective  and  timely manner,  will  result  in
    combined  results  of operations  and financial  condition superior  to what
    would have been achieved by each company independently, or as to the  period
    of  time required  to achieve such  result. The issuance  of Informix Common
    Stock in  connection  with the  Merger  will  have the  effect  of  reducing
    Informix's  net  income  per share  and  could  reduce the  market  price of
    Informix Common Stock unless  and until revenue growth  or cost savings  and
    other  business synergies sufficient  to offset the  effect of such issuance
    can be  achieved. There  can be  no assurance  that such  synergies will  be
    achieved.
 
        NEED FOR ACCEPTANCE OF OBJECT-RELATIONAL TECHNOLOGY.  The market for the
    object-relational database products of Illustra is new and evolving, and its
    growth  depends both  upon the  growing need to  store complex  data and the
    broader market acceptance of Illustra's object-relational technology as  the
    solution  for this  need. Because object-relational  technology represents a
    shift in programming  methodology, it requires  a substantial investment  in
    the  retraining  of  programmers,  which can  be  expensive  and  reduce the
    productivity of programmers during the  training period. As a result,  there
    can  be no assurance  that organizations will choose  to make the transition
    from   conventional    relational    database    management    systems    to
    object-relational  database management  systems, and  the time  frame within
    which such transition may occur, even if they believe that they can  benefit
    from  the  advantages  of  an object-relational  system.  Any  delay  in the
    market's acceptance of  object-relational database  management systems  will
    reduce  the anticipated  benefits of  the Merger  and could  have an adverse
    effect on Informix's results of operations and financial condition.
 
        COSTS OF  INTEGRATION; TRANSACTION  EXPENSES.   The combined  companies'
    results of operations will be adversely affected by Merger-related expenses,
    consisting  primarily  of  transaction costs  for  investment  bankers fees,
    attorneys,  accountants,  financial  printing  and  other  related   charges
    estimated  to be approximately $6  million dollars. These nonrecurring costs
    will be charged to operations in the  fiscal quarter in which the Merger  is
    consummated.  This  estimate  is  preliminary and  is  therefore  subject to
    change.
 
    FLUCTUATIONS IN QUARTERLY  RESULTS.  Informix's  operating results can  vary
substantially from period to period. The timing and amount of Informix's license
revenues  are subject to a  number of factors that  make estimation of operating
results prior to the end of a quarter extremely uncertain. Informix has operated
historically with little or no backlog, and as a result, license revenues in any
quarter are dependent on contracts entered into or orders booked and shipped  in
that  quarter. Informix's quarterly operating  margins have generally followed a
historic pattern,  with second  half revenues  and operating  margins  generally
being higher than those of the preceding first half. Informix believes that this
pattern  has been primarily related to customers' capital spending cycles at the
end of a calendar year as well  as to Informix's selling efforts, influenced  by
annual  sales incentive plans, at the end of the calendar year, which is the end
of Informix's  fiscal  year. Additionally,  as  is  common in  the  industry,  a
disproportionate   amount  of   Informix's  license  revenue   is  derived  from
transactions that  close in  the last  few weeks  of a  quarter. The  timing  of
closing   of   large   license   agreements   also   increases   the   risk   of
quarter-to-quarter fluctuations  and  the uncertainty  of  estimating  quarterly
 
                                       4

operating  results. Informix's operating expenses  are based on projected annual
and quarterly revenue levels, have been increasing at rates approaching the rate
of total revenue growth and  are incurred approximately ratably throughout  each
quarter.  As a result,  if projected revenues  are not realized  in the expected
period, Informix's operating results for that period would be adversely affected
as the operating  expenses are relatively  fixed in the  short term. Failure  to
achieve   revenue,  earnings  and  other  operating  and  financial  results  as
forecasted or anticipated by brokerage firm analysts or industry analysts  could
result  in an  immediate and  adverse effect on  the market  price of Informix's
Common Stock. Further, Informix may not learn of, or be able to confirm, revenue
or earning shortfalls until the  end of each quarter,  which could result in  an
even more immediate and adverse effect on the trading price of Informix's Common
Stock.
 
    VOLATILITY OF INFORMIX STOCK PRICES.  The market for Informix's Common Stock
is  highly  volatile. The  trading  price of  Informix's  Common Stock  could be
subject to wide fluctuations  in response to  quarterly variations in  operating
and  financial  results,  announcements  of  technological  innovations  or  new
products by Informix or its competitors, changes in prices of Informix's or  its
competitors'   products  and  services,  changes  in  product  mix,  changes  in
Informix's revenue  and revenue  growth rates  for Informix  as a  whole or  for
individual  geographic areas, business units, products or product categories, as
well as other events or factors. Statements or changes in opinions, ratings,  or
earnings  estimates made by brokerage firms or industry analysts relating to the
market in which Informix does business or relating to Informix specifically have
resulted, and could in the future result, in an immediate and adverse effect  on
the market price of Informix's Common Stock. Statements by financial or industry
analysts regarding the extent of the dilution in Informix's net income per share
resulting from the Merger and the extent to which such analysts expect potential
business  synergies to  offset such  dilution can  be expected  to contribute to
volatility in the market price of Informix Common Stock. In addition, the  stock
market  has from time to time  experienced extreme price and volume fluctuations
which have particularly  affected the market  price for the  securities of  many
high-technology  companies and which often have  been unrelated to the operating
performance of these  companies. These broad  market fluctuations may  adversely
affect the market price of Informix Common Stock.
 
    COMPETITION.   The market  for Informix's software  products and services is
extremely competitive.  The chief  competition faced  by Informix  is  currently
provided  by  Oracle  Corporation,  Sybase, Inc.,  CA  Ingres  (a  subsidiary of
Computer Associates International, Inc.), IBM Corporation, Microsoft Corporation
and Red Brick Systems,  Inc. and suppliers  of third party  tools such as  Gupta
Corporation,  Forte  Software,  Inc.  and  Dynasty  Technologies,  Inc.  Some of
Informix's current  competitors  and  many potential  competitors  have  greater
financial,  technical and marketing resources than  Informix. To the extent that
market acceptance for personal computer  oriented technologies increases at  the
expense  of UNIX or other  non-PC platforms, this could  result in greater price
pressure  on  certain  of  Informix's   database  products  and  services.   The
availability  and  market  acceptance  of  Microsoft  Corporation's  Windows  NT
operating system may increase the  competition faced by the principal  operating
system  platforms on which Informix's products operate and may result in greater
price pressure on certain  of Informix's database  products and services.  Also,
new or enhanced products introduced by existing or future competitors could have
an  adverse effect on  Informix's business, results  of operations and financial
condition. Existing and future competition  or changes in Informix's product  or
services  pricing structure or  product or service offerings  could result in an
immediate reduction in the  prices of Informix's products  or services. If  this
were  to result  in significant  price declines, the  effects of  which were not
offset by any  resulting increases  in sales  volume of  Informix's products  or
services,  Informix's business,  results of  operations and  financial condition
would be  adversely affected.  There  can be  no  assurance that  Informix  will
continue  to compete successfully with its  existing competitors or will be able
to compete successfully with new competitors.
 
    TECHNOLOGICAL CHANGE AND NEW PRODUCTS.   The market for Informix's  products
and  services is characterized  by rapidly changing  technology and frequent new
product introductions.  Informix's  success  will depend  upon  its  ability  to
enhance   its   existing   products   and   to   introduce   new   products   on
 
                                       5

a timely and cost-effective basis that meet dynamic customer requirements. There
can be no assurance that Informix will be successful in developing new  products
or  enhancing its existing products  or that such new  or enhanced products will
receive market acceptance  or be timely  delivered to the  market. Informix  has
experienced product delays in the past and may have delays in the future. Delays
in  the scheduled availability or a lack of market acceptance of its products or
failure to accurately  anticipate customer demand  or meet customer  performance
requirements  could  have  a  material adverse  effect  on  Informix's business,
results of operations and financial condition. In addition, products as  complex
as  those offered by Informix  may contain undetected errors  or bugs when first
introduced or as  new versions  are released. There  can be  no assurance  that,
despite  testing, new  products or  new versions  of existing  products will not
contain undetected errors or bugs that will delay the introduction or commercial
acceptance of such products. Informix's success  also depends on the ability  of
its  products  to  interoperate  and  perform  well  with  existing  and future,
industry-standard leading application software products  intended to be used  in
connection with relational database management systems. Failure to meet existing
and  future interoperability and performance requirements of certain independent
vendors marketing such applications  in a timely  manner could adversely  affect
the market for Informix's products. Commercial acceptance of Informix's products
and services could also be adversely affected by critical or negative statements
or  reports by  brokerage firms,  industry and  financial analysts  and industry
periodicals concerning Informix, its products, business or competitors or by the
advertising or marketing  efforts of  competitors, or other  factors that  could
affect consumer perception.
 
    INTERNATIONAL  OPERATIONS.  Over half of Informix's net revenues are derived
from its international operations.  Informix's operations and financial  results
could  be  significantly  affected  by  factors  associated  with  international
operations such as changes in foreign currency exchange rates and  uncertainties
relative  to  regional  economic  circumstances,  as  well  as  by  other  risks
associated with  international  activities.  Most  of  Informix's  international
revenue  and  expenses are  denominated in  local currencies.  Although Informix
takes into account changes in exchange rates over time in its pricing  strategy,
Informix's  business,  results of  operations and  financial condition  could be
materially and adversely affected by  fluctuations in foreign currency  exchange
rates.  There can be no assurance that Informix will not experience fluctuations
in international revenues.
 
    INTEGRATION OF ACQUIRED COMPANIES.  Informix has recently completed  several
acquisitions  including the database division of ASCII Corporation in Japan, STG
in the United States  and distributors in Germany,  Korea and Malaysia, and  has
recently  entered into  the Merger Agreement  to acquire  Illustra. Informix may
acquire other distributors, companies, products  or technologies in the  future.
There  can  be  no assurance  that  these  acquisitions and  the  acquisition of
Illustra can be effectively integrated,  that such acquisitions will not  result
in  costs  or  liabilities that  could  adversely effect  Informix's  results of
operations and financial condition, or that Informix will obtain the anticipated
or desired benefits of such acquisitions.
 
    KEY PERSONNEL.    Informix's  success  depends  in  part  on  the  continued
contributions  of both  companies' key  management and  technical personnel. The
success of Informix  also depends on  Informix's ability to  attract and  retain
other  qualified  technical,  managerial,  sales  and  marketing  personnel. The
competition for such personnel is intense in the software industry.  Uncertainty
during  integration of  the businesses  of Informix  and Illustra  may adversely
affect the combined companies' ability to attract and retain such personnel.
 
    MANAGEMENT OF  GROWTH.   Informix  has experienced  rapid growth  in  recent
years.  There can  be no  assurance Informix  will maintain  its recent  rate of
growth. Informix's  future growth  will depend  in part  on the  ability of  its
officers   and  key  personnel   to  manage  growth   successfully  through  the
implementation of  appropriate  management  systems  and  controls.  Failure  to
effectively  implement  or maintain  such systems  and controls  could adversely
affect Informix's business, results of operations and financial condition.
 
                                       6

    LIMITATIONS ON PROTECTION OF  INTELLECTUAL PROPERTY AND PROPRIETARY  RIGHTS.
Informix  relies on a combination of  trade secret, copyright and trademark laws
and contractual provisions  to protect  its proprietary rights  in its  software
products.  There can be no assurance that  these protections will be adequate or
that  competitors  will   not  independently  develop   technologies  that   are
substantially  equivalent  or superior  to  Informix's technology.  In addition,
copyright and trade secret protection for Informix's products may be unavailable
or unreliable in certain foreign countries. As of the date hereof, Informix  had
no  issued  patents. As  the number  of  software products  in the  industry and
software patents  increases,  Informix  believes that  software  developers  may
become  increasingly subject to  infringement claims. There  can be no assurance
that a third party will not assert that its patents or other proprietary  rights
are  violated by products offered by Informix.  Any such claims, with or without
merit, can be time consuming and expensive to defend, and could have an  adverse
effect  on Informix's business,  results of operations  and financial condition.
Infringement of valid  third party patents  and propriety rights  could have  an
adverse  effect  on Informix's  business,  results of  operations  and financial
condition. Informix  also relies  on "shrink-wrap"  break-the-seal licenses  not
signed by the licensee to protect its proprietary rights. "Shrink-wrap" licenses
may be unenforceable under the laws of certain jurisdictions.
 
    DEPENDENCE ON THIRD-PARTY PROVIDERS OF TECHNOLOGY.  The products of Informix
use   certain  products  and  technologies   of  various  third  party  software
developers, including both complete products offered as extensions of Informix's
product lines and  technology used  in the enhancement  of internally  developed
products.  Such  products and  technologies are  obtained  from the  third party
providers under  contractual license  agreements, which  in some  cases are  for
limited  time  periods and  in  some cases  provide  that such  licenses  may be
terminated under certain circumstances. There can be no assurance that  Informix
will  be able to  maintain adequate relations  with these third-party providers,
that these third-party providers will  commit adequate development resources  to
maintain these products and technologies or that the license agreements that are
for   limited  time   periods  will  be   renewed  upon   termination.  In  such
circumstances, Informix's inability to  obtain or develop substitute  technology
could  adversely affect Informix's business, results of operations and financial
condition.
 
    EFFECT OF ANTITAKEOVER  PROVISIONS OF  DELAWARE LAW  AND INFORMIX'S  CHARTER
DOCUMENTS.  Informix is subject to the provisions of Section 203 of the Delaware
General  Corporation Law, which has the effect of restricting changes in control
of a company. The Board of Directors of Informix is divided into three  classes,
with  each  class standing  for election  once every  three years.  In addition,
Informix's Board of Directors has authority  to issue up to 5,000,000 shares  of
preferred stock and to fix the rights, preferences, privileges and restrictions,
including  voting rights, of such  shares without any further  vote or action by
the stockholders. Informix  also has  a Preferred Shares  Rights Agreement  that
provides  for the issuance of rights which upon the occurrence of certain events
would result in significant dilution to  Informix Common Stock held by a  bidder
for Informix. These and other provisions of the Delaware General Corporation Law
applicable  to Informix and Informix's charter  documents may have the effect of
delaying, deterring or preventing changes in control or management of Informix.
 
                                       7

                              SELLING STOCKHOLDERS
 
    The following  table  shows,  as  to  each  Selling  Stockholder,  (i)  such
stockholder's  name  and  position  with  Informix  (including  its wholly-owned
subsidiary, STG), (ii) the number of  shares of Common Stock beneficially  owned
prior to the offering, and (iii) the number of shares of Common Stock to be sold
pursuant to this Prospectus:
 


                                                                         SHARES
                                                                      BENEFICIALLY       SHARES TO BE
                                                                     OWNED PRIOR TO          SOLD
NAME                                                                 OFFERING (1)(2)   IN THE OFFERING
- ------------------------------------------------------------------  -----------------  ----------------
                                                                                 
Jonathan Kraft Charitable Trust of 1996...........................          37,310(3)          37,310
David Lichtblau ..................................................         112,310(4)          28,000
 Vice President, Marketing
 Stanford Technology Group, Inc.
DPL I Charitable Trust............................................          56,000(5)          56,000
Sequoia Capital VI................................................          62,544(6)          62,544
Sequoia Technology Partners VI....................................           3,924(6)           3,924
Sequoia XXIV......................................................           3,140(6)           3,140
Kirill Sheynkman .................................................         112,310             32,110
 President, Stanford Technology Group, Inc.
Douglas M. Leone..................................................           2,218(7)           2,218
J. Thomas McMurray................................................           2,218(7)           2,218
Michael Moritz....................................................           2,218(7)           2,218
Thomas F. Stephenson..............................................           2,218(7)           2,218

 
- ------------------------
(1) Based on shares beneficially owned at January 17, 1996.
 
(2) No  Selling Stockholder will own  more than 1% of  the outstanding shares of
    Common Stock of Informix following the sale of the shares offered hereby.
 
(3) Excludes an  additional 75,000  shares  of Common  Stock owned  by  Jonathan
    Kraft,  the trustee of the  Jonathan Kraft Charitable Trust  of 1996 and the
    Vice President, Professional Services of Stanford Technology Group, Inc.
 
(4) Includes 56,000 shares of Common Stock  held by the DPL I Charitable  Trust,
    of which David Lichtblau is trustee.
 
(5) Excludes  56,310 shares of Common Stock held  by David Lichtblau, who is the
    trustee of the DPL I Charitable Trust.
 
(6) Excludes an aggregate  of 8,872  shares of  Common Stock  held severally  by
    Douglas  M.  Leone,  J.  Thomas  McMurray,  Michael  Moritz  and  Thomas  F.
    Stephenson, who  are  principals  of  Sequoia  Capital  and  its  affiliated
    entities.
 
(7) Excludes  an  aggregate of  69,608 shares  of Common  Stock held  by Sequoia
    Capital VI, Sequoia Technolgy  Partners VI and Sequoia  XXIV, as to each  of
    which Messrs. Leone, McMurray, Moritz and Stephenson are principals.
 
                              PLAN OF DISTRIBUTION
 
    Informix  has been  advised by  the Selling  Stockholders that  they and any
person receiving shares from the Selling Stockholders in the form of a bona fide
gift or distribution to a limited  partner of a Selling Stockholder (a  "Donee")
intend  to sell all or a portion of  the shares offered hereby from time to time
in the over-the-counter market and that sales will be made at prices  prevailing
at the times of
 
                                       8

such  sales. The Selling Stockholders and any  Donee may also make private sales
directly or through a broker or brokers,  who may act as agent or as  principal.
In  connection  with any  sales,  the Selling  Stockholders,  any Donee  and any
brokers participating in such sales may be deemed to be underwriters within  the
meaning  of the Securities Act. Informix will receive no part of the proceeds of
sales made hereunder.
 
    Any broker-dealer participating  in such transactions  as agent may  receive
commissions  from the Selling  Stockholders and any  Donee (and, if  they act as
agent for  the  purchaser  of  such shares,  from  such  purchaser).  Usual  and
customary brokerage fees will be paid by the Selling Stockholders and any Donee.
Broker-dealers  may  agree with  the Selling  Stockholders  to sell  a specified
number of shares  at a stipulated  price per share,  and, to the  extent such  a
broker-dealer  is unable to do  so acting as agent  for the Selling Stockholders
and any Donee, to purchase as principal any unsold shares at the price  required
to  fulfill the  broker-dealer commitment  to the  Selling Stockholders  and any
Donee. Broker-dealers who acquire shares as principal may thereafter resell such
shares from time to  time in transactions (which  may involve crosses and  block
transactions  and which may  involve sales to  and through other broker-dealers,
including transactions of  the nature described  above) in the  over-the-counter
market,  in negotiated transactions or otherwise  at market prices prevailing at
the time of sale or  at negotiated prices, and  in connection with such  resales
may pay to or receive from the purchasers of such shares commissions computed as
described above.
 
    Informix  has advised  the Selling  Stockholders that  the anti-manipulative
Rules 10b-6 and 10b-7  under the Exchange  Act may apply to  their sales in  the
market,  has furnished each Selling  Stockholder with a copy  of these Rules and
has informed them of  the need for  delivery of copies  of this Prospectus.  The
Selling   Stockholders  or  any  Donee  may  indemnify  any  broker-dealer  that
participates in transactions involving  the sale of  the shares against  certain
liabilities,  including  liabilities  arising  under  the  Securities  Act.  Any
commissions  paid  or  any  discounts   or  concessions  allowed  to  any   such
broker-dealers,  and any profits received  on the resale of  such shares, may be
deemed to be underwriting discounts and commissions under the Securities Act  if
any such broker-dealers purchase shares as principal.
 
    Upon notification by a Selling Stockholder or any Donee to Informix that any
material  arrangement has been entered into with a broker-dealer for the sale of
shares through a cross  or block trade, to  the extent required, a  supplemental
prospectus  will be  filed under  Rule 424(c)  under the  Securities Act setting
forth the  name of  the  participating broker-dealer(s),  the number  of  shares
involved, the price at which such shares were sold by the Selling Stockholder or
any  Donee,  the commissions  paid or  discounts or  concessions allowed  by the
Selling Stockholder or any Donee to such broker-dealer(s), and where applicable,
that such  broker-dealer(s) did  not  conduct any  investigation to  verify  the
information set forth in this Prospectus.
 
    Any securities covered by this Prospectus which qualify for sale pursuant to
Rule  144  under the  Securities Act  may be  sold under  that Rule  rather than
pursuant to this Prospectus.
 
    There can be no assurance that any of the Selling Stockholders or any  Donee
will sell any or all of the shares of Common Stock offered by them hereunder.
 
                                 LEGAL MATTERS
 
    The  validity of the shares  of Common Stock offered  hereby has been passed
upon  for  the  Company  by  Wilson  Sonsini  Goodrich  &  Rosati,  Professional
Corporation, Palo Alto, California.
 
                                       9