ABOUT HDF4.0 Beta 2
                   Nov 14, 1995
 
CONTENTS
 
     1. The mfhdf side library is renamed to libmfhdf.a,
        versus libnetcdf.a in previous releases
     2. New version of dimension record  
     3. New features
        GR interface
        Gzip library is added
        Unified configuration of library
        I/O performance improvement
     4. New functions added
        Fortran functions hxscdir and hxsdir         
        SDsetdimval_comp
        SDisdimval_bwcomp
     5. SGI Power Challenge running IRIX6.1 is now supported
     6. Pablo available  
     7. Platforms tested
     8. Changes in release notes 
     9. Bug fixes and Known problems


1. The mfhdf side library is renamed to libmfhdf.a, versus libnetcdf.a 
   in previous releases. To link a program with HDF4.0b2 libraries, 
   one needs four libraries, libmfhdf.a, libdf.a, libjpeg.a and libz.a 
   (see "Gzip library is added" in item 3 below):

      cc -o myprog myprog.c -I<path of include files> \
            libmfhdf.a libdf.a libjpeg.a libz.a

   Note, the order of the libraries is important.

2. New version of dimension record  
   HDF4.0b1 and previous releases use a vgroup to represent a dimension.
   The vgroup has a single field vdata with class "DimVal0.0".
   The vdata has <dimension size> number of records, each record has a
   fake value from 0, 1, 2 ... , (<dimension size> - 1 ). The fake values
   are not really required and take a lot of space. For applications that
   create large one dimensional array datasets the disk space taken by
   these fake values almost double the size of the HDF file. In order to
   omit the fake values, a new version of dimension vdata is proposed.

   The new version uses the same structure as the old version. The only
   differences are that the vdata has only 1 record with value
   <dimension size> and that the vdata's class is "DimVal0.1" to
   distinguish it from the old version. 

   No change is made in Unlimited dimensions. 
   
   See file dimval.txt in subdirectoy release_notes/ of HDF4.0b2 release
   for our policy on the backward compatibility of this dimension version.

3. New features
   . New with this beta release is the support for different methods of
     interlacing images in memory.  This feature is supported through the 
     GRreqlutil and GRreqimageil functions rescribed in the mf_ris.txt 
     document in this directory.  Please note that the images are 
     interlaced in memory only, all images are actually written to disk 
     in "pixel" interlacing.

   . Gzip library is added
     New with this release is support for gzip "deflate" style compression
     of any object in an HDF file.  This is supported through the standard
     compression interface function calls (HCcreate, SDsetcompress,
     GRsetcompress) by using the COMP_CODE_DEFLATE parameter for the coding
     type.  The comp_info structure has a new member, deflate.level, which
     specifies how much effort to expend trying to compress data.  Values
     for deflate.level must be between 1-9, with 1 being small amounts of
     effort (time) and 9 being maximum effort (most time and compression),
     the default value is 6.
     Currently, due to our use of the gzip "zlib" library for support of
     this feature, users must link with the "libz.a" library produced by
     zlib.  (See item1 above). 

          cc -o myprog myprog.c -I<path of include files> \
                  libmfhdf.a libdf.a libjpeg.a libz.a

     Note, the order of the libraries is important. 

     Also, this method of compression currently has several known bugs 
     when used on a 64-bit architecture (DEC Alpha processors, Cray 
     machines, and SGI Power Challenge machines in 64-bit "mode").

   . Unified configuration of library
     Both sides of the library now use the same configure script and
     can be configured uniformly through one makefile fragment. Please
     see the top-level INSTALL file in the distribution for further 
     details.

   . I/O performance improvement 
     This version of the distribution also has preliminary support for 
     file page buffering. Note that is a *Beta* release and is not 
     supported officially. As such it is is provided as is.
     The file page buffering allows the file to be mapped to user memory on 
     a per page basis i.e a memory pool of the file. With regards to the 
     file system, page sizes can be allocated based on the file system 
     page-size or if the user wants in some multiple of the file system 
     page-size. This allows for fewer pages to be managed along with 
     accommodating the users file usage pattern. Please see the 
     documentation in 'release_notes/page_buf.txt'.
     
     We have also reduced the memory requirements for several of the 
     internal HDF library data structures, for greater efficiency. 

4. Functions added
   . Fortran interface functions added for the set external path features.
     They are hxscdir and hxsdir.  See the man page of HXsetcreatedir(3)
     and HXsetdir(3) for detail.
   . SDsetdimval_comp -- sets backward compatibility mode for a dimension.
     The default mode is compatible in HDF4.0b2, and will be 
     incompatible in HDF4.1. See the man page of SDsetdimval_comp(3)
     for detail. 
   . SDisdimval_bwcomp(dimid) -- gets the backward compatibility mode
     of a dimension. See the man page of SDisdimval_bwcomp(3) for
     detail. 

5. SGI Power Challenge running IRIX6.1 is now supported
   Power Challenge is now supported, both in the native 64-bit and the 
   32-bit objects modes.  Note that the Power Challenge native 64 bits 
   objects use 64 bits long integers, users should be careful when using 
   the netcdf interface.  They should declare their variables as "nclong", 
   not "long".

6. Pablo available  
   This version of the distribution has support to create an 
   instrumented version of the HDF library(libdf-inst.a). This 
   library along the Pablo performance data capture libraries 
   can be used to gather data about I/O behaviour and procedure 
   execution times. Please see the documentation 
   release_notes/Pablo.txt in the distribution for further details.

7. Platforms tested
    HDF4.0b2 has been tested on the following systems:
    SunOS 4.1.3, SunOS 5.3 and 5.4(Solaris 2.3 and 2.4), 
    Linux_a.out, Linux_elf, SGI/IRIX5.2, SGI/IRIX5.3,
    SGI Power Challenge/IRIX6.1 (32- and 64-bit), HP/UX 9.01,
    IBM RS6000/AIX, Cray C90, Cray YMP, DEC alpha/UNIX (OSF), 
    DecStation/MIPSEL (ncdump doesn't work), Free BSD 2.0, 
    Solaris_x86, Convex Exemplar/HPUX, and CM5 parallel I/O. 
    See the INSTALL file at the top level of HDF4.0b2 for more 
    details.

8.  Changes in release notes
    The directory release_notes/ contains writeups for the alpha
    and beta releases of HDF4.0. Those files can be used as temporary
    documents for HDF4.0 before the official documentation is 
    available. 

    Newly added: ABOUT_4.0b2, Pablo.txt, dimval.txt, and page_buf.txt
    Files changed: bug_fixed.txt and parallel_CM5.txt.
    AOUBT_4.0.alpha is also included. 

9. Fixes and Known problems

   Problems fixed:
     . To avoid conflicts with C++, internal structures' fields which
       were named 'new' have been renamed.
     . Maximum number of fields in a vdata now is decided by VSFIELDMAX.
     . Vshow and hdp are fixed. Now they can handle as many fields 
       as defined by VSFIELDMAX.
     . Fixed platform number subclass problem when external data file was
       in Little_endian format. 
     . A file hdf/src/hlimits.h has been added to hold definitions for
       maximum number of open files and other limits. 
     . Miscelianeous fixes
   
   Known problems:
     . Hfidinquire not included in binaries
     . Gzip doesn't work on 64-bit machines.
     . Currently there is a problem in appending data to compressed objects.  
     . Hfidinquire is in the source code, but it is not included in the
       pre-compiled code. If your program uses Hfidinquire, you need to
       re-compile libdf.a.