## 12.6.5 BLOCKSIZE Specifier

The BLOCKSIZE specifier specifies the physical I/O transfer size 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.

For magnetic tape files, the value of bks specifies the physical record size in the range 18 to 32767 bytes. The default value is 2048 bytes.

For sequential disk files, the value of bks is rounded up to an integral number of 512-byte blocks and used to specify multiblock transfers. The number of blocks transferred can be 1 to 127; it is determined by RMS defaults.

For relative and indexed files, the value of bks is rounded up to an integral number of 512-byte blocks, and is used to specify the RMS bucket size in the range 1 to 63 blocks. The default is the smallest value capable of holding a single record.

For More Information:

- On setting RMS defaults, see the SET RMS_DEFAULT command in the OpenVMS DCL Dictionary.
- On tuning information, see the Guide to OpenVMS File Applications.

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