DISK1 Output

------- CC=00 HH=00 R=1 --------
----- CSW ------
00000D80  00000D78 0C0007E8 00000000 00000001  .......Y........

-----DATA BUFFER-----
00000E00  00060000 0000000F 03000000 00000001  ................
00000E10  00000000 00000000 00000000 00000000  ................

------- CC=00 HH=00 R=2 --------
----- CSW ------
00000D80  00000D78 0C000770 00000000 00000002  ................

-----DATA BUFFER-----
00000E00  07003AB8 40000006 31003ABE 40000005  ................
00000E10  08003AA0 00000000 06000000 20000000  ................
00000E20  00000000 00000000 00000400 00000000  ................
00000E30  00000000 00000000 00000000 00000000  ................
00000E40  00000000 00000000 00000000 00000000  ................
00000E50  00000000 00000000 00000000 00000000  ................
00000E60  00000000 00000000 00000000 00000000  ................
00000E70  00000000 00000000 00000000 00000000  ................
00000E80  00000000 00000000 00000000 00000000  ................

------- CC=00 HH=00 R=2 --------
----- CSW ------
00000D80  00000D78 0C0007B0 00000000 00000003  ................

-----DATA BUFFER-----
00000E00  E5D6D3F1 E3E7E7D6 E2F14000 00000101  VOL1TXXOS1......
00000E10  40404040 40404040 40404040 40404040  ................
00000E20  40404040 40404040 40C8C5D9 C3E4D3C5  .........HERCULE
00000E30  E2404040 40404040 40404040 40404040  S...............
00000E40  40404040 40404040 40404040 40404040  ................

------- VTOC FMT 4 DSCB --------
----- CSW ------
00000D80  00000D78 0C0007A0 00000000 00000101  ................

-----DATA BUFFER-----
00000E00  F4000000 01030D94 022B0000 00960001  4......M.....O..
00000E10  00000230 001E4B36 010B5209 02002F24  ................
00000E20  00000000 00000000 00000000 00000000  ................
00000E30  00000000 00000000 00000000 00010000  ................
00000E40  00000100 02000E00 00000000 00000000  ................
00000E50  00000000 00000000 00000000 00000000  ................

The first record CC=00 HH=00 R=1 is the first IPL record.  The residual length in the CSW is x’7E8′ so the record length as read is x’18’ (x’800′ – x’7E8′ = x’18’).  The second IPL record (R=2) is x’90’ in length.  The third record is the volume lable R=3 and is x’50’ (80 bytes) in length.  The first four bytes contain the label identifier ‘VOL1’, the next six bytes contain the volser followed by a space.  The next five bytes are the address of the VTOC.

I have highlighted several fields of interest in the Format 4 DSCB.

  • Offset x’00’ is one byte x’F4′ (C’4′) identifying this as a Format 4 DSCB
  • Offset x’12’ is a halfword containing the number of cylinders on the volume
  • Offset x’14’ is a halfword containing the number of tracks/cylinder (x’1E’)
  • Offset x’16’ is the track length
  • Offset x’1E’ is the number of DSCB’s per track
  • Offset x’1F’ is the number of directory blocks per track
  • Offset x’3D’ is the beginning of a 10-byte extent descriptor
  • Offset x’3F’ is 4 bytes with the beginning CCHH for the VTOC (0000 0001)
  • Offset x’43’ is 4 bytes with the ending CCHH of the VTOC (0002 000E)

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