When the amount of space required is expressed in average record length, you must specify the number of records within the data set and their average length. Use the AVGREC keyword to modify the scale of your request. When AVGREC is specified, the first subparameter of SPACE becomes the average record length. The system applies the scale value to the primary and secondary quantities specified for the SPACE keyword. Possible values for the AVGREC keyword follow:

   U—Use a scale of 1
   K—Use a scale of 1024
   M—Use a scale of 1048576

When the AVGREC keyword is specified, the values specified for primary and secondary quantities in the SPACE keyword are multiplied by the scale and those new values will be used in the space allocation. For example, the following request results in the primary and secondary quantities being multiplied by 1024:

   //  DD SPACE=(80,(20,2)),AVGREC=K, ...
 
                         80  = average record length in bytes
    80 * 20 * 1024 = 1.6 MB  = primary space
    80 *  2 * 1024 = 160 KB  = secondary space, to be allocated if the
                               primary space is not enough

For an extended-format data set, the operating system uses a value 32 larger than the above block size. The primary and secondary space are divided by the block length to determine the number of blocks requested. The operating system determines how many blocks of the block length can be written on one track of the device. The primary and secondary space in blocks is then divided by the number of blocks per track to obtain a track value, as shown in the examples below. These examples assume a block length of 23200. Two blocks of block length 23200 can be written on a 3380 device:

   (1.6MB / 23200) / 2 = 36 = primary space in tracks
   (160KB / 23200) / 2 =  4 = secondary space in tracks