GEOS VLIR

Later on in the life of the C64, the GEOS OS came out. It was  a  system much like many other windowing OS's (MAC OS,  Windows)  in  that  it  used icons, windows, a mouse pointer and resource drivers. In order to  contain all the information needed for the windowing system (icon, window position, creation time/date), a new filetype called VLIR was needed  and  directory changes were made. While GEOS files might not be of interest to many of the emulator users, it is likely that these files  will  be  encountered,  and knowledge of them would be helpful.

There are actually two types of GEOS files, VLIR and  SEQuential. Don't confuse the GEOS SEQuential type with that of the standard D64  SEQ  file. They are related, but not the same. VLIR are  described  in  more  detail following this paragraph. GEOS SEQuential files are  all  non-VLIR  files, including normal PRG, USR and SEQ types.

GEOS files usually have an entity attached  called  an  INFO  block. It contains ICON info, author, file description, load address  etc.  However, just because an INFO block does not exist for a given file, does not  mean that the file is not a GEOS file.

Each GEOS VLIR file or application is comprised of many separate  chains (called RECORDS) for different sections of the app/file. Each RECORD can be loaded in separately and overtop of other ones. Below is  a  dump  of  the first directory sector of the GEOS 2.0 disk. Note the  first  entry  seems normal enough, but the rest have additional information  in  the  normally unused section of the entry.

00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F --- 00: 12 04 82 13 00 47 45 4F 53 20 56 32 2E 30 20 45  <- Normal entry 10: 4E 47 4C 2E A0 00 00 00 00 00 00 00 00 00 58 00 20: 00 00 83 02 02 44 45 53 4B 20 54 4F 50 A0 A0 A0 <- First GEOS file. 30: A0 A0 A0 A0 A0 02 0F 01 04 58 08 13 0D 23 78 00 <- Note extra info 40: 00 00 83 0B 13 43 4F 4D 4D 20 31 33 35 31 28 61    from offset $15 to  50: 29 A0 A0 A0 A0 08 0F 00 0A 58 05 09 15 24 03 00     $1D. 60: 00 00 83 0F 0D 4D 50 53 2D 38 30 31 A0 A0 A0 A0 70: A0 A0 A0 A0 A0 0F 05 00 09 56 07 19 01 00 04 00 80: 00 00 83 08 0D 43 4F 4E 46 49 47 55 52 45 A0 A0 90: A0 A0 A0 A0 A0 08 05 01 0E 58 05 1F 0B 31 4E 00 A0: 00 00 83 01 10 50 41 49 4E 54 20 44 52 49 56 45 B0: 52 53 A0 A0 A0 01 08 00 06 57 08 0C 0E 00 12 00 C0: 00 00 83 0B 05 70 72 65 66 65 72 65 6E 63 65 20 D0: 6D 67 72 A0 A0 0B 12 00 05 56 0A 09 13 2D 16 00 E0: 00 00 83 08 11 70 61 64 20 63 6F 6C 6F 72 20 6D F0: 67 72 A0 A0 A0 08 07 00 05 58 05 19 0C 10 16 00

Lets analyze the second entry to see what's all involved with GEOS files. Note, the offset values have been changed to 0 to make referencing easier.

00: 00 00 83 02 02 44 45 53 4B 20 54 4F 50 A0 A0 A0 10: A0 A0 A0 A0 A0 02 0F 01 04 58 08 13 0D 23 78 00

Byte:  $02: C64 filetype (see the section on D64 for an explanation) REL files are not allowed. 03-04: Starting track/sector (02/02 from above) of C64 file if GEOS filetype is $00. If GEOS filetype is non-zero, track/sector of single-sector RECORD block 05-14: Filename (in ASCII, padded with $A0, case varies) 15-16: Track/sector location of info block 17: GEOS file structure $00 - Sequential 01 - VLIR file 18: GEOS filetype $00 - Non-GEOS (normal C64 file) 01 - BASIC 02 - Assembler 03 - Data file 04 - System File 05 - Desk Accessory 06 - Application 07 - Application Data (user-created documents) 08 - Font File 09 - Printer Driver 0A - Input Driver 0B - Disk Driver (or Disk Device) 0C - System Boot File 0D - Temporary 0E - Auto-Execute File 0F-FF - Undefined 19: Year (1900 + value) 1A: Month (1-12, $01 to $0C) 1B: Day (1-31, $01 to $1F) 1C: Hour (0-23, $00 to $17) in military format 1D: Minute (0-59, $00 to $3B) 1E-1F: Filesize, in sectors (low/high byte order)

If the values at byte $18 is 00 then we have a normal,  sequential,  C64 file, without an info block. If the value at byte $18  is  anything  other than 00, we have a GEOS file, be it VLIR or sequential, with an info block.

One big addition to the directory is the TIME STAMP contained at $19-$1D. The year is simply the number 1900 plus whatever is stored at that location so the year 2005 would have a $69 (105 decimal) stored there. The rest  of the values are limited as described above.

The INFO BLOCK stores items like the  ICON,  size,  load  address,  file types, description, etc, and is always only 1 sector long. Since there is a fixed space to store information, the ICON height, width and bitmap length must be the same. Here is a sample info block, and layout...

00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F      ASCII ---   00: 00 FF 03 15 BF 3F 83 F8 40 44 04 8E 38 E2 B5 93  ????+??°@D??8?+? 10: 59 AA 92 A9 B5 93 59 AA 92 A9 BF 93 F9 B1 93 19 Y???+?Y???+????? 20: 8E 10 E1 BB 93 B9 B5 93 59 AA 92 A9 B5 93 59 AE ??????+?Y???+?Y? 30: 92 E9 B1 93 19 80 10 01 BF 93 F9 FF D7 FD 80 38 ????????+??????8 40: 03 FF FF FF 83 05 00 00 2E D9 54 00 2E 50 68 6F ????????.+T?.Pho 50: 74 6F 20 4D 67 72 20 20 20 56 32 2E 31 00 00 00 to?Mgr???V2.1??? 60: 00 43 68 72 69 73 20 48 61 77 6C 65 79 00 00 00 ?Chris?Hawley??? 70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????  80: 00 00 00 00 00 00 00 00 00 53 61 76 65 20 70 68  ?????????Save?ph 90: 6F 74 6F 20 69 6D 61 67 65 73 20 69 6E 20 61 20 oto?images?in?a? A0: 53 61 76 65 20 70 68 6F 74 6F 20 69 6D 61 67 65 Save?photo?image B0: 73 20 69 6E 20 61 20 70 68 6F 74 6F 20 61 6C 62 s?in?a?photo?alb C0: 75 6D 20 66 6F 72 20 6C 61 74 65 72 20 75 73 65 um?for?later?use D0: 20 69 6E 20 67 65 6F 57 72 69 74 65 20 6F 72 20 ?in?geoWrite?or? E0: 67 65 6F 50 61 69 6E 74 2E 00 02 85 06 85 07 85 geoPaint.??????? F0: 08 85 09 85 16 A9 04 85 11 A9 00 85 10 4C 2F C2 ?????????????L/+

Byte: $00-01: Contains $00/$FF since its only 1 sector long 02-04: Information sector ID bytes (03 15 BF). The "03" is likely the bitmap width, and the "15" is likely the bitmap height, but rare exceptions do exist to this! 05-43: Icon bitmap (sprite format, 63 bytes) 44: C64 filetype (same as that from the directory entry) 45: GEOS filetype (same as that from the directory entry) 46: GEOS file structure (same as that from the dir entry) 47-48: Program load address 49-4A: Program end address (only with accessories) 4B-4C: Program start address 4D-60: Class text (terminated with a $00) 61-74: Author (with application data: name of  application  disk,                terminated with a $00. This string may not  necessarily  be                set, or it may contain invalid data) The following GEOS files have authors: 1 - BASIC 2 - Assembler 5 - Desk Accessory 6 - Application 9 - Printer Driver 10 - Input Driver 75-88: If a document, the name of the application that created it. 89-9F: Available for applications, unreserved. A0-FF: Description (terminated with a $00)

Note: all the text strings above are in ASCII, not PETASCII.

If the file is a VLIR, then the RECORD block is of interest. This single sector is made up of up to 127 track/sector pointers, each of which  point to program sections (called RECORDS). VLIR files are comprised of loadable RECORDS (overlays, if you wish to use PC terminology). The first RECORD is what is always loaded first when you run that application. After that, the OS loads whatever RECORD it needs. Here is a partial sample of the  RECORD sector...

00: 00 FF 08 00 09 04 09 03 0A 0A 0B 11 0F 11 00 00 10: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 20: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

Byte: $00-01: Contains 00/FF since its only 1 sector long 02-03: Starting track/sector (8,0) for the first RECORD 04-05: Starting track/sector (9,4) for the second RECORD 06-07: Starting track/sector (9,3) for the third RECORD 08-09: fourth RECORD (10/10) 0A-0B: fifth RECORD (11/17) 0C-0D: sixth RECORD (15/17) 0E-0F: seventh RECORD (0/0)

When a T/S link of $00/$00 is encountered, we are  at  the  end  of  the RECORD block. If the T/S link  is  a  $00/$FF,  then  the  record  is  not available.

Note that if you add up the sectors so far, we have only used  two,  one for the INFO sector and one for the RECORD sector. Obviously there are more used, and they are contained in the sector chains from the RECORD  sector. Each t/s link in the RECORD sector points to a chain of sectors, the length of which is included in the sector  count  for  the  GEOS  file. Doing a VALIDATE on a GEOS disk when not in GEOS would de-allocate all these sector chains (and the RECORD sector as well), which would not be good!

Below is the dump of a BAM sector from a GEOS-formatted  D64  image  and there are some changes for GEOS. We have all the typical data (forward t/s pointer to 18/1, DOS type, disk name/id) but we also have  the  GEOS-format signature from $AB-BC. From observation, any GEOS-formatted disk will have the GEOS signature written in the same place (offset $AB)  in  the  sector that contains the disk name/ID.

00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F      ASCII ---   00: 12 01 41 00 13 FE DF 1F 0A 69 29 0D 15 FF FF 1F  ??A??????i)?????  10: 0C 96 D6 16 01 00 00 10 00 00 00 00 11 FD BD 1D  ????????????????  20: 15 FF FF 1F 0C 96 D6 16 00 00 00 00 00 00 00 00  ????????????????  30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????  40: 00 00 00 00 00 00 00 00 0F FC FD 05 00 00 00 00  ????????????????  50: 00 00 00 00 06 05 05 05 01 00 40 00 00 00 00 00  ??????????@?????  60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????  70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ????????????????  80: 00 00 00 00 00 00 00 00 01 00 02 00 11 FF FF 01  ????????????????  90: 41 70 70 6C 69 63 61 74 69 6F 6E 73 A0 A0 A0 A0  Applications????  A0: A0 A0 4A 44 A0 32 41 A0 A0 A0 A0 13 08 47 45 4F  ??JD?2A??????GEO  B0: 53 20 66 6F 72 6D 61 74 20 56 31 2E 30 50 BD 1E  S?format?V1.0P??  C0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ???????????????? D0: 00 00 00 00 00 00 00 00 00 00 00 18 2D 00 00 00 ????????????-??? E0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ???????????????? F0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????

Bytes:$00-01: Track/Sector location of the first directory sector (should               be 18,1, but it doesn't seem to matter) 02: Disk DOS version type $41=1541           03: $2A, DOS version. 04-8F: BAM entries for each track, in groups of  four  bytes  per track, starting on track 1 90-9F: Disk Name (padded with $A0) A0-A1: Filled with $A0 A2-A3: Disk ID           A4: Usually $A0 A5-A6: DOS type, usually "2A" A7-AA: Filled with $A0 AB-AC: Border sector trk/sec (see below) AD-BC: GEOS ID string ("GEOS format V1.x", in ASCII) BD-DC: Unused (usually $00) DD-FF: Free sector info for tracks 36-70,  used  on  double-sided 1571 disks only!

The first two bytes at $AB/$AC ($13 $08) are the track/sector location of the BORDER SECTOR, which is one sector long, has  the  same  layout  as  a normal directory sector, and is used for copying files  from  one  disk  to another. When you need to copy a file, you drag the icon to the bottom  of the screen and the file is moved from its normal location in the  directory to the border sector. Since it is only  1  sector,  it  can  only  hold  8 entries.

If you want to check to see if a disk is formatted for GEOS,  check  the string in the BAM sector starting at $AD (offset 173) for the string "GEOS format". If it does not match, the disk is not in GEOS format. This is the way that GEOS itself verifies if a disk is GEOS formatted.

On a D64/1541, here is how GEOS allocates blocks as it either saves files or needs blocks for other purposes:

Saving files: When there's still at least one free block  in  the  current track, then the next block is searched for starting at the sector which is away from the current one by at least the soft interleave. The exceptions are track 25 and above  where  the  interleave  changes  to  the  original interleave _minus one_.

When stepping to the next track, the sector where the next  block  of  the files is saved to is computed as following:

New sector = (Next track - Previous Track) * 2 + 4 + Soft interleave

Getting the Border Sector: When allocating the  GEOS  border  sector,  the search starts upwards from sector 19/0 for a free  sector  and  then  from sector 1/0 if no free one has been found yet.

Getting the first sector for saving a file: Start searching from sector 1/0 and, on the first track that has at  least  one  free  sector,  you  start searching at the sector computed by the form above.

How to detect if a file is GEOS
1. Check the bottom 3 bits of the D64 file type (byte position $02 of  the directory entry). If it is not 0, 1 or 2 (but  3  or  higher,  REL  and above), the file cannot be GEOS.

2. Check the FILE STRUCTURE and FILE TYPE bytes (byte position $23 and $24 respectively). If they are both $00, then the file is not GEOS, but is a normal D64 filetype (no INFO block either).

3. Check the FILE STRUCTURE byte (position $23). If it is  anything  other than $00 or $01, then the file is not GEOS (as those are the only legal values).

4. If you've reached this point, and everything looks ok, then the file is GEOS. Now, if the FILE STRUCTURE byte (position $23) is a $01, then the file is a GEOS VLIR, othersize it is a GEOS SEQ.

5. Check the FILE TYPE byte (position $24). If it is non-zero, then  there is likely an INFO block attached. Check the  track/sector  pointer  at position $21/22 to see if they are valid numbers (track within the specs of the disk and sector in range for the track value). If they look good, then the info block exists.

(Content taken from GEOS.TXT in Peter Scheper's compendium of c64 file formats)