14. File Input and Output
  This chapter explains BASIC file organizations and record
  operations that are implemented through OpenVMS VAX
  Record Management Services (RMS). For a more thor-
  ough understanding of file organization and file and record
  operations, see the OpenVMS Record Management Services
  Reference Manual .

  RMS stores data in physical blocks . A block is the smallest
  number of bytes BASIC transfers in a read or write opera-
  tion. On disk, a block is 512 bytes. On magnetic tape, it is 18
  to 8192 bytes.

  RMS stores one or more data records in each block. A data
  record can also be divided into smaller units, called fields . A
  data record can be smaller than, equal to, or larger than a
  disk block.