How Found
The VOLVTOC field of the standard volume label contains the format-4 address. The format-4 DSCB is always the first record in the VTOC.
Table 1 shows the contents of a format-4 DSCB.
Exception: The format-4 DSCB has a 44-byte
key of X'04' bytes not shown in Table 1.
| Offset Dec (Hex) | Type | Length | Name | Description |
|---|---|---|---|---|
| 0(X'00') | Character | 1 | DS4IDFMT | Format identifier (X'F4'). |
| DS4IDC | Constant value of X'F4' in DS4FMT. | |||
| 1(X'01') | Character | 5 | DS4HPCHR | Highest address (CCHHR) of a format-1 DSCB. |
| 6(X'06') | Unsigned | 2 | DS4DSREC | Number of available DSCBs. |
| 8(X'08') | Character | 4 | DS4HCCHH | CCHH of next available alternate track. |
| 12(X'0C') | Unsigned | 2 | DS4NOATK | Number of remaining alternate tracks. |
| 14(X'0E') | Bitstring | 1 | DS4VTOCI | VTOC indicators. |
| 1 . . . . . . . | DS4DOSBT | VSE bit. Either invalid format 5 DSCBs or indexed VTOC. Previously DOS(VSE) bit. See DS4IVTOC. | ||
| . 1 . . . . . . | DS4DVTOC | Index was disabled. | ||
| . . 1 . . . . . | DS4EFVLD | Extended free-space management flag. When DS4EFVLD is on, the volume is in OSVTOC format with valid free space information in the format-7 DSCBs. See also DS4EFLVL and DS4EFPTR. | ||
| . . . 1 . . . . | DS4DSTKP | VSE stacked pack. | ||
| . . . . 1 . . . | DS4DOCVT | VSE converted VTOC. | ||
| . . . . . 1 . . | DS4DIRF | DIRF bit. A VTOC change is incomplete. | ||
| . . . . . . 1 . | DS4DICVT | DIRF reclaimed. | ||
| . . . . . . . 1 | DS4IVTOC | Volume uses an indexed VTOC. | ||
| 15(X'0F') | Unsigned | 1 | DS4NOEXT | Number of extents in the VTOC(X'01'). |
| 16(X'10') | Bitstring | 1 | DS4SMSFG | System managed storage indicators. |
| 00 . . . . . . | DS4NTSMS | Non-system managed volume. | ||
| 01 . . . . . . | DS4SMSCV | System managed volume in initial status. | ||
| 10 . . . . . . | Reserved. | |||
| 11 . . . . . . | DS4SMS | System managed volume. | ||
| 11 . . . . . . | DS4SMSTS | System managed volume. | ||
| . . xx xxxx | Reserved. | |||
| 17(X'11') | Binary | 1 | DS4DEVAC | Number of alternate cylinders when the volume was formatted. Subtract from first 2 bytes of DS4DEVSZ to get number of useable cylinders (can be 0). Valid only if DS4DEVAV is on. |
| 18(X'12') | Character | 14 | DS4DEVCT | Device constants. For currently supported devices, these fields do not provide enough information to calculate the amount of space used on a track. Use TRKCALC (see Performing Track Calculations (TRKCALC macro)). |
| 18(X'12') | Character | 4 | DS4DEVSZ | Device size. |
| 18(X'12') | Binary | 2 | DS4DSCYL | Number of logical cylinders including alternates, if any exist. Unsigned number. Set to X'FFFE' for devices with more than 65,520 cylinders, indicating that cylinder-managed space exists (DS4CYLMG is set on) and extended attribute DSCBs, formats 8 and 9, are allowed. |
| 20(X'14') | Binary | 2 | DS4DSTRK | Number of tracks in a logical cylinder. |
| 22(X'16') | Unsigned | 2 | DS4DEVTK | Device track length. |
| 24(X'18') | Binary | 2 | DS4DEVOV | Keyed record overhead. |
| 24(X'18') | Binary | 1 | DS4DEVI | Non-last-keyed record overhead. |
| 25(X'19') | Binary | 1 | DS4DEVL | Last keyed record overhead. |
| 26(X'1A') | Binary | 1 | DS4DEVK | Non-keyed record overhead differential. |
| 27(X'1B') | Bitstring | 1 | DS4DEVFG | Flag byte 1. |
| . . . 1 . . . . | DS4DEVAV | Value in DS4DEVAC, number of alternate cylinders is valid. Otherwise, the number is not available in this DSCB. | ||
| . . . . 1 . . . | Keyed record overhead field (DS4DEVOV) is used as a 2-byte field to specify the overhead required for a keyed record. | |||
| . . . . . 1 . . | The CCHH of an absolute address is used as a continuous binary value. Not implemented in the current IBM® product line. | |||
| . . . . . . 1 . | The CCHH of an absolute address is used as four separate binary values. Not implemented in the current IBM product line. | |||
| . . . . . . . 1 | A tolerance factor must be applied to all but the last block of the track. Not implemented in the current IBM product line. | |||
| xxx. . . . . | Reserved. | |||
| 28(X'1C') | Binary | 2 | DS4DEVTL | Device tolerance. |
| 30(X'1E') | Binary | 1 | DS4DEVDT | Number of DSCBs per track. |
| 31(X'1F') | Binary | 1 | DS4DEVDB | Number of PDS directory blocks per track. |
| 32(X'20') | Binary | 8 | DS4AMTIM | VSAM time stamp. |
| 40(X'28') | Character | 3 | DS4AMCAT | catalog indicator. |
| 40(X'28') | Bitstring | 1 | DS4VSIND | VSAM indicators. |
| 1 . . . . . . . | DS4VSREF | A catalog references this volume. | ||
| . 1 . . . . . . | DS4VSBAD | The VSAM data sets on this volume are unusable because an MSS CONVERTV command has not completed successfully for the volume. (No longer set.) | ||
| . .1 . . . . . | DS4VVDSA | Bit on indicate VVDS does exist | ||
| . .1 . . . . . | DS4VVDSR | If on, VVDS data set name was scanned. It is turned on once per volume when the VVDS was scanned on the volume. | ||
| . . .x xxxx | Reserved. | |||
| 41(X'29') | Unsigned | 2 | DS4VSCRA | Relative track location of the CRA. |
| 43(X'2B') | Binary | 8 | DS4R2TIM | VSAM volume/catalog match time stamp. |
| 51(X'33') | Character | 5 | Reserved. | |
| 56(X'38') | Character | 5 | DS4F6PTR | Pointer (CCHHR) to first format-6 DSCB, or zero. (No longer supported as non-zero). |
| 61(X'3D') | Character | 10 | DS4VTOCE | VTOC extent description. |
| 71(X'47') | Character | 10 | Reserved. | VTOC extent description. |
| 81(X'51') | Character | 1 | DS4EFLVL | Extended free-space management level. X'00' indicates extended free-space management is not used for this volume. X'07' indicates extended free-space management is in use for this volume (see also DS4EFVLD). |
| 82(X'52') | Character | 5 | DS4EFPTR | Pointer to extended free-space information. If DS4EFLVL=X'00' this is zero. If DS4EFLVL=X'07' this is the CCHHR of the first FMT-7 DSCB and no format-5 DSCBs contain free space information. |
| 87(X'57') | Character | 1 | DS4MCU | Minimum allocation size in cylinders for cylinder-managed space. Each extent in this space must be a multiple of this value. |
| 88(X'58') | Character | 4 | DS4DCYL | Number of logical cylinders. Valid when DS4DSCYL= X'FFFE'. |
| 92(X'5C') | Character | 2 | DS4LCYL | First cylinder address/4095 where space is managed in multicylinder units. Cylinder-managed space begins at this address. Valid when DS4CYLMG is set. |
| 94(X'5E') | Character | 1 | DS4DEVF2 | Device Flags Byte 2 |
| 1... .... | DS4CYLMG | Cylinder-managed space exists on this volume and begins at DS4LCYL in multicylinder units of DS4MCU. DS4EADSCB is also set when this flag is on. | ||
| .1.. .... | DS4EADSCB | Extended attribute DSCBs, Format 8 and 9 DSCBs, are allowed on this volume. | ||
| ..xx xxxx | Reserved | |||
| 95(X'5F') | 1 | Reserved | ||
| 96(X'60') | DS4END | - |