SQL> select component,GRANULE_SIZE from  v$sga_dynamic_components
  2  /

COMPONENT                                                        GRANULE_SIZE
---------------------------------------------------------------- ------------
shared pool                                                          16777216
large pool                                                           16777216
buffer cache                                                         16777216

-- shows a granule size of 16M for my SGA

SQL> show parameter sga_max_size

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
sga_max_size                         big integer 336679728

-- For eg)
SQL> show parameter db_cache_size

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_cache_size                        big integer 218103808
SQL> select 218103808/1024/1024 "DB_Cache_Size(M)
  2  " from dual;

DB_Cache_Size(M)

-----------------
              208

-- its currently 208MB
-- trying to set it to 200M

SQL> alter system set db_cache_size= 200m;

System altered.

SQL> show parameter db_cache_size

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_cache_size                        big integer 218103808

-- but its still 208MB, becos of the granule size 16M. Oracle rounds off to the multiple of granule size.

SQL> select CURRENT_SIZE from v$sga_dynamic_components where COMPONENT='buffer cache';

CURRENT_SIZE
------------
   218103808

SQL> alter system set db_cache_size=192m;

System altered.

-- but when I try to set it to a multiple of 16M, say to 192M, it resizes exactly to that value specified.

SQL> select value/1024/1024 "size(M)" from v$parameter where name='db_cache_size';

   size(M)
----------
       192

-- the granule size is dependent on SGA size. If the total SGA size is < 128M , Granule_size = 4M , else Granule_size = 16M on most platforms. On 32 bit NT,however its 8M for sga_size > 128M.