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Data structure that precedes all of the standard UEFI table types.


typedef struct {
  UINT64 Signature;
  UINT32 Revision;
  UINT32 HeaderSize;
  UINT32 CRC32;
  UINT32 Reserved;


Member Description
Signature A 64-bit signature that identifies the type of table that follows. Unique signatures have been generated for the EFI System Table, the EFI Boot Services Table, and the EFI Runtime Services Table.
Revision The revision of the UEFI Specification to which this table conforms. The upper 16 bits of this field contain the major revision value, and the lower 16 bits contain the minor revision value. The minor revision values are limited to the range of 00..99.
HeaderSize The size, in bytes, of the entire table including the EFI_TABLE_HEADER
CRC32 The 32-bit CRC for the entire table. This value is computed by setting this field to 0, and computing the 32-bit CRC for HeaderSize bytes.
Reserved Reserved field that must be set to 0.


  • The capabilities found in the EFI system table, runtime table and boot services table may change over time. The first field in each of these tables is an EFI_TABLE_HEADER. This header’s Revision field is incremented when new capabilities and functions are added to the functions in the table. When checking for capabilities, code should verify that Revision is greater than or equal to the revision level of the table at the point when the capabilities were added to the UEFI specification.
  • Unless otherwise specified, UEFI uses a standard CCITT32 CRC algorithm with a seed polynomial value of 0x04c11db7 for its CRC calculations.
  • The size of the system table, runtime services table, and boot services table may increase over time. It is very important to always use the HeaderSize field of the EFI_TABLE_HEADER to determine the size of these tables.

Copyright (C) 2009 Phoenix Technologies Ltd. All Rights Reserved. Portions copyright (C) 2008 UEFI Forum, Inc. Used with permission

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