*** GEOS VLIR (Variable Length Index Record) ** Document revision 1.1 Later on in the life of the C64, an OS called GEOS came out. It was a system much like the many 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. 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. Each GEOS 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 whats 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 (19xx) 1A: Month (1-12) 1B: Day (1-31) 1C: Hour (0-23, military time) 1D: Minute (0-59) 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. 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 ----------------------------------------------- 00: 00 FF 03 15 BF FF FF FF 92 49 01 FF FF 01 80 00 10: 1D BF FF DD A0 00 5D BF FF C1 A0 00 5D A1 C6 55 20: A0 29 5D A0 C9 41 A1 09 41 B9 D6 41 A8 00 41 BF 30: FF C1 80 00 1D 9C 00 15 9C 00 15 80 00 1D 80 00 40: 01 FF FF FF 83 04 01 56 19 55 19 75 51 64 65 73 50: 6B 54 6F 70 20 41 4D 20 20 56 32 2E 30 00 00 00 60: 00 50 65 74 65 72 20 53 63 68 65 70 65 72 73 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 00 4C 2A 5B 4C 59 5D 4C 90: A7 61 4C 3A 62 AD 8A 84 D0 01 60 20 7E 23 20 9C A0: 55 73 65 20 74 68 65 20 64 65 73 6B 54 6F 70 20 B0: 74 6F 20 6D 61 6E 61 67 65 20 61 6E 64 20 6D 61 C0: 6E 69 70 75 6C 61 74 65 20 79 6F 75 72 20 66 69 D0: 6C 65 73 2E 00 03 20 E3 5C 68 85 FB 20 4F 61 20 E0: 13 61 20 32 61 20 F2 5C A9 0C 20 CC 49 A9 2E 85 F0: 13 A9 F9 85 12 A9 2F 85 15 A9 01 85 14 A9 84 85 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! There are also changes to the BAM sector from a normal D64 file. Looking at the D64 entry from before, we have all the normal information, plus the new information starting at $AB: 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/ssec (*see below) AD-BC: GEOS ID string ("GEOS format V1.0", in ASCII) BD-DC: Unused (usually $00) DD-FF: Free sector info for tracks 36-70, used on double-sided 1571 disks only! 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. Note: GEOS disks contain something called a "border sector" which is also only 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 hold only 8 entries. 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. Seeing as this is not an emulator format, I will not comment on its relative merits. It is simply another C64 file type.