Attachment B: Preboot Execution Environment

To enable the interoperability of clients and downloaded bootstrap programs, the client preboot code must provide a set of services for use by a downloaded bootstrap. It also must ensure certain aspects of the client state at the point in time when the bootstrap begins executing. The services provided by the client for use by the bootstrap are as follows:

• Preboot Services API. Contains several global control and information functions.
  
  
• TFTP API. Enables opening and closing of TFTP connections, and reading packets from and writing packets to a TFTP connection.
  
  
• UDP API. Enables opening and closing UDP connections, and reading packets from and writing packets to a UDP connection.
  
  
• Universal NIC Driver Interface (UNDI) API. Enables basic control of and I/O through the client&rsquo’s network interface device.

  The aspects of the client&rsquo’s state to be ensured by the client preboot code at the point in time that execution of the downloaded bootstrap is initiated are as follows:

• The use of certain portions of the client&rsquo’s main memory
  
  
• The settings of certain portions of the client&rsquo’s interrupt vector
  
  
• The settings of certain of the client&rsquo’s CPU registers

  Note: The descriptions in subsequent sections are specific to Intel-architecture PCs. A processor architecture-independent description of these interface and state specifications is probably possible, but has not been attempted.