Added information about commodore formats

2025-12-16 19:24:38 +00:00 · 2015-03-25 02:19:24 +00:00
parent a110d79c87
commit 712ac67072
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+
+*** REL (RELative file layout)
+*** Document revision: 1.1
+*** Last updated: March 11, 2004
+*** Compiler/Editor: Peter Schepers
+*** Contributors/sources: Immers/Neufeld "Inside Commodore DOS"
+
+  This is a filetype native to CBM drive (random access)  devices.  On  the
+surface it seems similar to all other filetypes, especially  SEQ,  but  was
+designed to make access to data *anywhere* in the file very fast.
+
+  We start by examining a REL file directory entry...
+
+00: 00 00 84 11 02 41 44 44 49 54 49 4F 4E 41 4C 20  <20><><EFBFBD>..ADDITIONAL<41>
+10: 49 4E 46 4F A0 11 0C FE 00 00 00 00 00 00 61 01  INFO<46>..<2E><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>a.
+
+     Bit:$00-01: Track/Sector location of next directory sector ($00 $00 if
+                 not the first entry in the sector)
+             02: File type.
+                 Typical values for this location are:
+                   $00 - Scratched (deleted file entry)
+                    80 - DEL
+                    81 - SEQ
+                    82 - PRG
+                    83 - USR
+                    84 - REL
+                 Bit 0-3: The actual filetype
+                          000 (0) - DEL
+                          001 (1) - SEQ
+                          010 (2) - PRG
+                          011 (3) - USR
+                          100 (4) - REL
+                          Values 5-15 are illegal, but if used will produce
+                          very strange results. The 1541 is inconsistent in
+                          how it treats these bits. Some routines use all 4
+                          bits, others ignore bit 3,  resulting  in  values
+                          from 0-7.
+                 Bit   4: Not used
+                 Bit   5: Used only during SAVE-@ replacement
+                 Bit   6: Locked flag (Set produces ">" locked files)
+                 Bit   7: Closed flag  (Not  set  produces  "*", or "splat"
+                          files)
+          03-04: Track/sector location of first sector of file
+          05-14: 16 character filename (in PETASCII, padded with $A0)
+          15-16: Track/Sector location of first side-sector block (REL file
+                 only)
+             17: REL file record length (REL file only, max. value 254)
+          18-1D: Unused (except with GEOS disks)
+          1E-1F: File size in sectors, low/high byte  order  ($1E+$1F*256).
+                 The approx. filesize in bytes is <= #sectors * 254
+
+  The third byte ($84) indicates this entry is a  REL  file  and  that  the
+three normally empty entries at offset $15, $16 and $17  are  now  used  as
+they are explained above. It's the sector chain that this entry  points  to
+(called the SIDE SECTORS)  which  are  of  interest  here  (in  this  case,
+#17/#12). Here is a dump of that sector...
+
+      00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F       ASCII
+      -----------------------------------------------  ----------------
+0000: 0C 13 00 FE 11 0C 0C 13 06 09 00 00 00 00 00 00  <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+0010: 11 02 11 0D 11 03 11 0E 11 04 11 0F 11 05 11 10  <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+0020: 11 06 11 11 11 07 11 12 11 08 11 13 11 09 11 14  <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+0030: 11 0A 11 0B 10 00 10 0A 10 14 10 08 10 12 10 06  <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+0040: 10 10 10 04 10 0E 10 02 10 0C 10 01 10 0B 10 03  <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+0050: 10 0D 10 05 10 0F 10 07 10 11 10 09 10 13 0F 07  <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+0060: 0F 11 0F 05 0F 0F 0F 03 0F 0D 0F 01 0F 0B 0F 00  <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+0070: 0F 0A 0F 14 0F 08 0F 12 0F 06 0F 10 0F 04 0F 0E  <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+0080: 0F 02 0F 0C 0F 09 0F 13 0E 07 0E 11 0E 05 0E 0F  <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+0090: 0E 03 0E 0D 0E 01 0E 0B 0E 00 0E 0A 0E 14 0E 08  <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+00A0: 0E 12 0E 06 0E 10 0E 04 0E 0E 0E 02 0E 0C 0E 09  <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+00B0: 0E 13 0D 07 0D 11 0D 05 0D 0F 0D 03 0D 0D 0D 01  <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+00C0: 0D 0B 0D 00 0D 0A 0D 14 0D 08 0D 12 0D 06 0D 10  <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+00D0: 0D 04 0D 0E 0D 02 0D 0C 0D 09 0D 13 0C 07 0C 11  <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+00E0: 0C 05 0C 0F 0C 03 0C 0D 0C 01 0C 0B 0C 00 0C 0A  <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+00F0: 0C 14 0C 08 0C 12 0C 06 0C 10 0C 04 0C 0E 0C 02  <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
+
+  Bytes:   $00: Track location of next side-sector ($00 if last sector)
+            01: Sector location of next side-sector
+            02: Side-sector block number (first sector is $00, the next  is
+                $01, then $02, etc)
+            03: REL file RECORD size (from directory entry, max. value 254)
+         04-0F: Track/sector locations of the six other side-sectors.  Note
+                the first entry is this very sector we  have  listed  here.
+                The next is the next t/s listed at  the  beginning  of  the
+                sector. All of this information must be correct. If one  of
+                these chains is $00/$00, then we have no more side sectors.
+                Also, all of these (up to six) side sectors must  have  the
+                same values in this range.
+         10-FF: T/S chains of *each* sector of the data  portion.  When  we
+                get a $00/$00, we are at the end of the chain.
+
+  If the speed advantage regarding this type file file isn't  obvious  yet,
+consider the following scenario... If we need to access  record  4000,  its
+only a couple of calculations to see how many bytes into the file it is...
+
+  4000 * "record length" (254) = byte offset
+
+  Once we know this, we can calculate how many sectors into  the  file  the
+  record is...
+
+  byte offset / 254 = # of sectors into REL file
+
+  The divisor value "254" in the above  formula  is  the  number  of  bytes
+useable in each sector (256 bytes less the 2 bytes used for the forward t/s
+pointer) and has no relation to the "max REL record length".
+
+  Now that we know the number  of  sectors,  we  can  look  it  up  in  our
+side-sector tables to see where the record is. The speed of this system  is
+truly amazing, given the era of the C64, and a floppy drive.
+