*** CVT (ConVerT containers)
*** Document revision: 1.3
*** Last updated: Oct 1, 2007
*** Compiler/Editor: Peter Schepers
*** Contributors/sources: Joe Forster/STA

  These are sequential representations of GEOS files, both  sequential  and
VLIR. In order to be transmitted and up/downloaded, they must be  converted
to this intermediate format because the file's INFO block (and record block
for a VLIR) must be included. Note that the track/sector references at  the
beginning of each sector are not included here, making the block  size  254
bytes. Also, any values in track/sector references are invalid,  since  the
value is sure to change once the file is converted back from CVT to a  GEOS
format.

  I will not include much of the GEOS file layout details here, as you  can
read the GEOS.TXT document to get the information.

  With CVT's that contain VLIR files, there  are  four  distinct  sections:
signature, info, record and data. CVT's that contain non-VLIR  files  (i.e.
standard GEOS sequential) do not include the record block.

  The first part, which exists in both CVT types, is the  signature  block.
It contains the complete directory entry and CVT file signature.

      00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F        ASCII
      -----------------------------------------------   ----------------
0000: 83 00 00 44 45 53 4B 20 54 4F 50 A0 A0 A0 A0 A0   ���DESK�TOP�����
0010: A0 A0 A0 00 00 01 04 58 08 13 0D 23 78 00 50 52   �����..X...#x�PR
0020: 47 20 66 6F 72 6D 61 74 74 65 64 20 47 45 4F 53   G�formatted�GEOS
0030: 20 66 69 6C 65 20 56 31 2E 30 00 00 00 00 00 00   �file�V1.0������
0040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
0050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
0060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
0070: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
0080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
0090: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
00A0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
00B0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
00C0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
00D0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
00E0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
00F0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 .. ..   ��������������..

    Byte:$00-1D: Complete directory entry. Note that the first two bytes of
                 *any* directory entry are never used,  and  thus  are  not
                 incuded here either.
          1E-39: File signature. It can contain "PRG formatted..." or  "SEQ
                 formatted...". Here we can check that the  CVT  is  really
                 what it claims.
          3A-FD: Usually $00

What follows the signature block is the complete GEOS file INFO block.

      00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F        ASCII
      -----------------------------------------------   ----------------
00F0: .. .. .. .. .. .. .. .. .. .. .. .. .. .. 03 15   ................
0100: BF FF FF FF 92 49 01 FF FF 01 80 00 1D BF FF DD   �����I.��.��.���
0110: A0 00 5D BF FF C1 A0 00 5D A1 C6 55 A0 29 5D A0   ��]�����]��U�)]�
0120: C9 41 A1 09 41 B9 D6 41 A8 00 41 BF FF C1 80 00   �A�.A��A��A�����
0130: 1D 9C 00 15 9C 00 15 80 00 1D 80 00 01 FF FF FF   .��.��.��.��.���
0140: 83 04 01 56 19 55 19 75 51 64 65 73 6B 54 6F 70   �..V.U.uQdeskTop
0150: 20 41 4D 20 20 56 32 2E 30 00 00 00 00 42 72 69   �AM��V2.0����Bri
0160: 61 6E 20 44 6F 75 67 68 65 72 74 79 00 00 00 00   an�Dougherty����
0170: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
0180: 00 00 00 00 00 4C 2A 5B 4C 59 5D 4C A7 61 4C 3A   �����L*[LY]L�aL:
0190: 62 AD 8A 84 D0 01 60 20 7E 23 20 9C 55 73 65 20   b����.`�~#��Use�
01A0: 74 68 65 20 64 65 73 6B 54 6F 70 20 74 6F 20 6D   the�deskTop�to�m
01B0: 61 6E 61 67 65 20 61 6E 64 20 6D 61 6E 69 70 75   anage�and�manipu
01C0: 6C 61 74 65 20 79 6F 75 72 20 66 69 6C 65 73 2E   late�your�files.
01D0: 00 03 20 E3 5C 68 85 FB 20 4F 61 20 13 61 20 32   �.��\h���Oa�.a�2
01E0: 61 20 F2 5C A9 0C 20 CC 49 A9 2E 85 13 A9 F9 85   a��\�.��I�.�.���
01F0: 12 A9 2F 85 15 A9 01 85 14 A9 84 85 .. .. .. ..   .�/�.�.�.���....

  The third block is the RECORD block. In the  sequential  version  of  the
CVT, this block won't exist. The way  to  tell  if  the  file  is  VLIR  or
sequential is to look at byte position 23  of  the  directory  entry  (from
above, it's value is $01). If it's a $00, the file is sequential,  if  it's
$01 it's VLIR.

      00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F        ASCII
      -----------------------------------------------   ----------------
01F0: .. .. .. .. .. .. .. .. .. .. .. .. 43 41 0A 0B   ............CA..
0200: 0B F4 0A 8C 0B A1 09 70 00 00 00 00 00 00 00 00   .���.��p��������
0210: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
0220: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
0230: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
0240: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
0250: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
0260: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
0270: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
0280: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
0290: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
02A0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
02B0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
02C0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
02D0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
02E0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ����������������
02F0: 00 00 00 00 00 00 00 00 00 00 .. .. .. .. .. ..   ����������......

  Note that the RECORD block is modified  from  the  original  GEOS  entry.
Instead of containing the track and sector  references,  we  now  have  the
sector count and the size of the last sector in the chain. Looking over the
block above, we get the following usage chart:

      Count  Size   Comment
      -----  ----   --------------------------------------
       43     41    Sector count=67, last sector index=$41
       0A     0B    Sector count=10, last sector index=$0B
       0B     F4    Sector count=11, last sector index=$F4
       0A     8C    Sector count=10, last sector index=$8C
       0B     A1    Sector count=11, last sector index=$A1
       09     70    Sector count=9,  last sector index=$70
       00     00    No more records.

Two things of interest can be noted from the record block...

  1. When a 00/00 is encountered, the record block is done.
  2. When a 00/FF is encountered,  the  record  does  not  exist  (see  the
     GEOS.TXT format for more info on invalid records), but the entry  must
     still be made in the re-created RECORD block.

  From here on we have the actual data, all of  the  record  chains  strung
together to form one long file. All of this data must be  broken  apart  to
form the original records that GEOS expects.

      00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F        ASCII
      -----------------------------------------------   ----------------
02F0: .. .. .. .. .. .. .. .. .. .. A9 00 8D EE 04 A4   ..........����.�
0300: FE B9 86 84 30 06 29 0F C9 02 D0 12 A4 70 B9 86   ����0.).�.�.�p��
0310: 84 30 06 29 0F C9 02 D0 05 A9 07 8D A0 1D 20 1E   �0.).�.�.�.��.�.
0320: 23 20 04 1A 8A D0 20 20 12 1A 18 A9 00 6D F4 03   #�..����...��m�.
0330: 8D F4 03 A9 03 6D F5 03 8D F5 03 20 C5 22 20 7C   ��.�.m�.��.��"�|
0340: 1B 20 04 1A 20 6B 1A A9 08 8D A0 1D B8 50 53 8D   .�..�k.�.��.�PS�
0350: EE 04 20 12 1A A2 00 A4 70 20 3F 24 C9 04 B0 3F   �.�..���p�?$�.�?