Some SAS Data Sets and other SAS Files must be converted for use in Version 9.1 if they were created in earlier versions. The PROCedure provided by SAS for this purpose is PROC MIGRATE.

Note that PROC MIGRATE does not work on all Version 8 files. Attempted conversion of some files will result in the message

ERROR: <catalog or data set name> was created under a diferent
  operating system

In most cases, this probably refers to the difference between the 32-bit operating system under which Version 8.x was running and the 64-bit operating system under which Version 9.x runs. Regardless of the specific reason, the solution virtually always is to use PROC CPORT/PROC CIMPORT to do the conversion. This method is documented at

/www.usc.edu/its/doc/statistics/sas/faq/acrossystems/proc-cport.html

SAS Institute has explained the situation to us as follows:

SAS 9 users can safely interchange data files with SAS 8 users under certain circumstances. The most straight forward example of interchanging data files with a SAS 8 user is one where the SAS 9 data file is created and used in a SAS 8 session within the same operating system family. It is therefore, considered native to the operating system. As long as features have not been used which were not available in the prior version, such as long format names, this file can be used "as is". For information regarding SAS 9 features which may make the data file incompatible with SAS 8, please see
support.sas.com/rnd/migration/planning/files/forward.html

SAS 9 was released under certain unix platforms as a 64 bit application. If you run SAS in a 64 bit environment, then create a SAS 9 data set and try to read it in a SAS 8 session running in a 32 bit environment on the same machine, Cross Environment Data Access (CEDA) will enable you to use the data set with certain restrictions. Catalogs can not be accessed at all without cporting them to transport format and cimporting them into the SAS 8 session. Bear in mind, cport will only work for catalogs, in this instance. As a general rule, cport is used to move data sets and catalogs from one release to the same release or higher.

If CEDA is used to translate the file, you cannot update it. When you process the file, you may notice a slight reduction in performance. Also, CEDA does not support indexing and will not use any index associated with the file. You can confirm whether CEDA is being used to read the file, by first setting the system option MSGLEVEL=I, then, running a procedure on all or some of the observations in the data set. You can also run PROC CONTENTS in a SAS 9 session.

Under the field DATA REPRESENTATION, you will see 'foreign' if it is anything other than the operating system you are using.

The message in the log using MSGLEVEL=i, follows if CEDA is being used.

   INFO: Data set is in a foreign host format. Cross Environment Data
   Access will be used, which may require additional CPU resources and
   reduce performance.

If you've confirmed that CEDA is being used to process the data file, you can use PROC COPY with the NOCLONE option to copy it and remove the processing restrictions.

Here is an example.

libname noCEDA 'path-to-folder-containing-foreign-file';
PROC COPY IN=noCEDA OUT=temp NOCLONE;
/*Make sure to use the SELECT statement */
/*otherwise, the whole library will be copied */
  SELECT dsname;
RUN;

You can also use the DATA STEP. When you create a new data set, it will be created in the native data representation of the operating system under which you are currently running and remove the CEDA restrictions.

Here is an example.

DATA new;
SET dsname;
RUN;

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SOURCE: eMail from SAS Institute Consultant, 9 December 2004

In addition to the links shown above, please visit the following sites

support.sas.com/rnd/migration/resources/procmigrate/

support.sas.com/rnd/migration/planning/platform/64bit.html

for documentation and more information.