# OPEN: BLOCKSIZE Specifier

The BLOCKSIZE specifier indicates the physical I/O transfer size in bytes for the file. It takes the following form:

BLOCKSIZE = bks

bks | Is a scalar numeric expression. If necessary, the value is converted to integer data type before use.

If you specify a nonzero number for bks, it is rounded up to a multiple of 512 byte blocks. The maximum valid value of BLOCKSIZE is 2147467264.

If you do not specify BLOCKSIZE or you specify zero for bks, the default value of 128 KB (131,072 bytes) is assumed. However, if you compile with the assume buffered_stdout option, the default blocksize for stdout is 8 KB.

The default BLOCKSIZE value can be changed by using the FORT_BLOCKSIZE environment variable or by specifying the BLOCKSIZE parameter on the unit's OPEN. The BLOCKSIZE value can be changed for stdout by re-opening the unit corresponding to stdout with an explicit BLOCKSIZE parameter; for example:

    OPEN(6,ACCESS='SEQUENTIAL',FORM='FORMATTED',BUFFERED='YES',BLOCKSIZE=1048576

Parent topic: OPEN Statement Specifiers