DCB

Key Characteristics

• • Defines dataset attributes for I/O operations
  • Can be specified in JCL or programs
  • Merged from multiple sources at execution
  • Required for all dataset access
  • Controls data formatting and buffering
• DCB Parameters:
  • DSORG: Dataset organization (PS, PO, DA, IS)
  • RECFM: Record format
  • F (Fixed)
  • V (Variable)
  • B (Blocked)
  • A (ASA carriage control)
  • M (Machine carriage control)
  • LRECL: Logical record length
  • BLKSIZE: Block size
  • BUFNO: Number of buffers
  • MACRF: Macro form (access method macros)
• DCB Merging Hierarchy:
  1. Program DCB specifications 2. JCL DD statement DCB parameters 3. Dataset label information 4. System defaults
• • FB: Fixed blocked records (most common)
  • VB: Variable blocked records
  • FBA: Fixed blocked with ASA control
  • VBA: Variable blocked with ASA control
  • U: Undefined format (programmer-controlled)

Use Cases

• • Defining file characteristics in batch programs
  • Specifying tape dataset attributes
  • Creating new datasets with specific formats
  • Overriding cataloged dataset attributes
  • Interfacing with VSAM and non-VSAM files

Related Concepts