NUMBUFG parameter

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Number of above-the-bar buffers


Default value
Parameter type
Where set
Not resettable
Related products
Model 204 V7.1


Allocate this number of buffer pool buffers above the bar (ATB).

  • Prior to version 7.7 of Model 204:

    NUMBUFG specifies the number of buffer pool buffers built ATB, while the number of buffer pool buffers built BTB is based on the setting of MINBUF, MAXBUF, and SPCORE.

  • As of version 7.7:

    If NUMBUFG is specified, no buffer pool buffers are built BTB; all buffers are ATB. Model 204 obtains exactly the NUMBUFG number of buffers.

    In this case, NUMBUFG essentially replaces the BTB parameters: NUMBUF and MINBUF are automatically reset to 0, and MAXBUF and SPCORE are ignored.


The maximum number of buffers is 2**31/3, or 715,827,882, which limits buffer pools to 4.2 terabytes or less.

The minimum number of ATB buffers is:


If you set NUMBUFG to a value lower than the minimum, the value is reset to the calculated value and you receive messages like the following:

*** M204.2756: NUMBUFG reset to NLRUQG * ((NSERVS + NSUBTKS) * MAXOBUF + 15) = 1 * ((2+9) * 4 + 15) = 59 *** M204.0075: Initialization completed. Buffers = 0+59


If you set NUMBUFG greater than 0:

  • The X'02' bit of the XMEMOPT parameter (the default), must also be set.
  • The FLOD and FILELOAD commands and Fast/Reload are not available due to 64-bit addressing conflicts. This particular restriction is removed in V7.7 and later releases.

See also

For more information about setting NUMBUFG, see Using 64-bit addressing and Above the Bar (ATB) storage.