
*** Introduction to the various Emulator File Formats

***  Compiled by:    Peter Schepers
***      Started:   August 24, 1996
*** Last updated:       Nov 7, 2008

---------------------------------------------------------------------------

  There are always questions asked regarding the various file formats which
are commonly used on either the emulators or the real C64. Most  often  the
question involves conversion... "What do I do with LNX files?" or "How do I
make these files work on the C64s emulator?". These  documents  attempt  to
explain their internal structure, what to do with them, and some  of  their
respective strengths and weaknesses.

  These documents were compiled and written in an attempt to unify all  the
other smaller files dealing with Commodore file  types  that  are  floating
about the net, or that exist with other programs.  They  are  by  no  means
exhaustive (even though they look like it), but attempts will  be  made  to
keep them up-to-date, and correct anything which  is  wrong.  If  you  spot
something that needs correcting please make sure to  email  the  author  so
that corrections  can  be  made  for  future  releases...  the  address  is
contained later in this document.

  Some of the information contained in these documents may not be  accurate
as it could have  been  taken  from  inaccurate  sources,  and  I  have  no
first-hand experience with said  format.  However,  use  these,  pass  them
around, upload them, whatever. Just be sure to  leave  them  INTACT,  don't
remove bits.

  I have attempted to categorize the filetypes involved using  three  basic
categories: IMAGES, ARCHIVES and CONTAINERS. The definitions  for  each  of
these categories can be found at the bottom of this document.

  Also, plenty of good information can be  gleaned  from  the  source  code
contained in the archive CBMConvert, which is on the FTP.FUNET.FI FTP site.
Contained in it are the sources for UnZipCode, UnLNX, Ark, some  LHA  info,
etc. It is an invaluable set of utilities put together by both Marko Makela
and Paul Doherty.


  So far, this document covers the following files:

  * D64 images (1541 disks and some variants)
  * X64 images (for the X64/Vice emulator)
  * T64 containers (for the C64s emulator)
  * T64 .FRZ (FRoZen Files, saved emulator sessions for C64s)
  * PC64 containers (P/S/U/Rxx)
  * PC64 .C64 (saved emulator sessions for PC64)
  * D71 images (1571 disks)
  * D81 images (1581 disks)
  * D80 (8050) & D82 (8250) floppy images
  * G64 images (GCR copy of a 1541 disk)
  * D2M images (FD2000 disks)
  * DNP images (CMD hard disk native partitions)
  * F64 (not an image file, but a companion file to D64's)
  * N64 (64NET's custom files)
  * L64 (64LAN's custom files)
  * C64 (PCLINK's custom files)
  * CRT images (CCS64 ROM cartridges)
  * 64x (PC64 ROM files)
  * TAP images (for CCS64, sampled cassette tapes)
  * VSF VICE snapshots (saved-emulator sessions for VICE)
  * WAV Audio RIFF files for the PC

  ...as well as the following native C64 types,  some  of  which  are  also
  supported on the various emulators:

  * Extensive disk file layout (how files are stored on 1541/71/81 disks)
  * 4-file diskpacked ZipCode archives (or .Z64, 4 or 5 files, #!xxxxx)
  * 6-file SixPack ZipCode images (or .Z64, #!!xxxx)
  * Filepacked ZipCode archives (or .Z64, x files, x!xxxxx)
  * LNX containers (LyNX)
  * ARK containers & SRK archives (ARKive & compressed ARKive)
  * LHA & LZH archives (header description only)
  * SFX archives (SelF-eXtracting LHA/LZH)
  * SDA archives (Self-Dissolving Archive)
  * ARC archives (ARChive)
  * ZIP archives (PKZIP)
  * CKIT archives (Compression KIT)
  * CPK containers
  * WRA & WR3 archives (Wraptor, version 1 to 3)
  * LBR containers (LiBRary, C64 only, not the C128 CP/M .LBR files)
  * GEOS VLIR files (Variable Length Index Record)
  * REL files (RELative)
  * CVT files (GEOS ConVerT)
  * SPY containers (SPYne)
  * C128 Boot Sector layout
  * Binary & PRG (PRoGram, with load address)
  
  Also included is a very basic look at some C64 graphic bitmap formats (in
BITMAP.TXT), and the  saved  session  layout  of  the  Macintosh-based  C64
emulator "Power64" (in POWER64.TXT). Thanks to Peter Weighill for the above
info.

  Joe Forster/STA has written up a description of how the various Commodore
drives (1541/1571/1581) allocate sectors and directory entries when  saving
files (under normal mode and under GEOS). It is included as DISK.TXT

  Right now there are several good utilities available to work with most of
the mentioned formats. The first is 64COPY, my own conversion program.  The
second is Star Commander, by Joe Forster/STA. Included with his program are
many smaller utilities such as Star ARK, Star LHA and Star ZIP, which  will
convert specific formats to D64 images.

                                                 Peter Schepers,
                                                 University of Waterloo.

                                          Email: schepers@ist.uwaterloo.ca

---------------------------------------------------------------------------

Most recent changes:

Jun  2/04 - Changes to the D2M.TXT document.

Nov 27/05 - Renamed D2M to D2M-DNP.TXT & extensively updated
          - Updated GEOS.TXT
          - Updated D80-D82.TXT
          - Updated CRT.TXT with new CRT types 19-23

Feb 21/06 - Updated CRT.TXT with new CRT types 24-27

Jun 12/07 - Updated CRT.TXT with sample CRT's for types 24-27

Oct  1/07 - Updated VICE_FRZ.TXT with info about the bogus ".S64"  snapshot
            file extension from the UnQuill package.
          - Updated D81.TXT doc
          - Updated D71.TXT doc
          - Updated G64.TXT doc
          - Updated CVT.TXT doc

Feb 19/08 - Updated G64.TXT, removed erroneous odd/even tail gap info.
          - Updated D64.TXT with other SpeedDOS clone names

Nov 7/08 - Updated D64, D71,  D81  &  D80/D82  with  extra  explanation  of
           oversize directory track images, which contain more  files  than
           normal.

---------------------------------------------------------------------------

*** Terms and acronyms

  Many strange terms have come along with computers in general, and I  will
not attempt to explain them all, but some of the ones in this document  may
not be entirely clear. I will attempt to make things  a  little  easier  by
explaining some of the more common ones.


  <CR> - Short form for a Carriage Return ($0D) symbol.

  <LF> - Short form for a Line Feed ($0A) symbol.

  ARCHIVE - A  file  format  which  contains  other  files,  and  in  which
            compression is an integral part of the  design.  Some  examples
            are ZIP, SRK, SDA, ARC, LHA, WRA.

  ASCII - This is an acronym for "American Standard  Code  for  Information
          Interchange". The standard  is  a  7-bit  code  covering  control
          codes, punctuation, alphanumeric (A to Z, 0 to 9) as well as math
          and a few other symbols. Since it is a 7-bit code, it ranges from
          $00 to $7F (0-127). This leaves the top 128-255 definable by  the
          vendor. The PC world has corrupted this standard making it 8-bit.

  BAM - An acronym for "Block Availability Map". Here  is  where  the  disk
        operating system keeps track of  what  sectors  are  allocated  (or
        available) for each track.

  BLOCK - This refers to sectors which  on  a  logical  level  are  grouped
          together. On a 1541 disk, it could be a series of sectors  linked
          together in a file, or a partition on a  1581  disk.  In  the  PC
          world it represents a "cluster"  of  sectors.  Generally  if  I'm
          referring to a grouping of sectors thats *not* 256  bytes  large,
          then I talk in blocks.

  BYTE - A group of 8 bits, the contents of a memory location.

  CHAIN - A series of sectors linked  together.  One  sector  will  have  a
          pointer to another, and that sector will point to another,  until
          the chain has no more forward pointers. A file stored on  a  1541
          disk would be considered a chain of sectors, but it  also  has  a
          directory entry explaining what the chain is for.

  CONTAINER - A file format which  simply  contains  other  files,  and  no
              compression takes place. Some examples  are  T64,  P00,  SPY,
              ARK, LNX.

  FILETYPE - In the Commodore world, this would be the kind of file, be  it
             SEQ, REL, PRG, USR, GEOS etc. In the  DOS  world,  this  would
             possibly be the file extension, be it EXE, TXT, DOC. It  tells
             the user what file it is, making usage easier.

  GCR - An acronym for "Group Code Recording". This is the encoding  method
        Commodore uses to physically store the information on most  of  the
        5.25" disks (i.e. 1541). It encodes an  8  bit  sequence  (2  4-bit
        nybbles) into a 10 bit sequence (2  5-bit  nybbles)  so  that  long
        repeated sequences of 1's or 0's are avoided. These must be avoided
        so that the timing of reading/writing to the disk won't become "out
        of sync". As a user, you would not normally see the GCR information
        since the drive does all the conversion to normal HEX  data  before
        it gives it to you.

  HIGH/LOW - The bytes here are stored backwards compared to  the  LOW/HIGH
             method. See LOW/HIGH for more information.

  IMAGE - A file format which is a PC equivalent of  a  physical  Commodore
          media. Some examples are D64 (1541), D71 (1571), D81 (1581),  D2M
          (FD2000), X64.

  LINK - This is the track/sector values, stored in the first two bytes  of
         a sector, which point to (or "link" to) the t/s  location  of  the
         next sector. A  series  of  these  links  comprise  a  "chain"  of
         sectors.

  LOW/HIGH - This is how values are stored when they  exceed  one  byte.  A
             good example of this is the sector count of  a  D64  file.  To
             calculate the actual value, take the second value, multiply it
             by 256 and add the low  value.  You  will  now  get  the  real
             decimal value. i.e. (HIGH*256)+LOW=result.

             If you look at is as a HEX value, swap the  bytes  around  and
             put them together for the 16-bit HEX value. i.e. $FE $03 would
             be $03FE as a 16-bit HEX value.

  LSB/MSB - See LOW/HIGH.

  LSU - This is my own acronym meaning "last  sector  useage".  It  is  the
        value stored in byte position $01 (the "sector" value  of  the  t/s
        link) of the last sector of a file. This value is the offset  into
        the sector where the last byte is stored. It  also  represents  the
        byte count + 1, since a value of 255 would actually mean  only  254
        bytes of file data exists (full sector less the  2  bytes  for  t/s
        chain). Without reasonable knowledge of the disk layout, this  byte
        can be confusing, and hard to explain.

  NYBBLE - A grouping of 4 bits (half a byte), either the first or  last  4
           bits of an 8-bit binary number,  or  one  half  of  a  two-digit
           hexadecimal number.

           Typically, a byte will be broken down into two parts, the top  4
           bits and the bottom 4 bits. These are referred to as  the  upper
           and lower  nybble  respectively,  and  are  represented  by  two
           hexadecimal digits in base 16.

  PETASCII - (or PETSCII) This is Commodore's version  of  ASCII  (the  PET
             part of the name comes from the  first  computer  to  use  the
             code, the PET or Personal Electronic Transactor).

             Most of the codes from 0-127 are the same as ASCII, but  there
             are differences, especially  noticible  when  converting  text
             from a C64  to  a  DOS  machine.  Where  ASCII  has  uppercase
             characters, PETASCII has lower  case  ones,  and  vice  versa.
             Also, the top 128 characters (128 to 255) are quite  different
             from the PC "standard".

  RLE - An acronym for "Run Length Encoding". This is a simple  compression
        method, employed by most compression programs,  and  also  used  by
        some file formats (ZipCode, CPK). It encodes sequences (or  "runs",
        hence the name "RUN length...") of the same byte (i.e. 00 00 00  00
        00 00) into a smaller string using a shorter code sequence,  making
        the resultant file smaller than the original. This is the  simplest
        form of file compression.

  SECTOR - It is best described as the method that the drive uses to  store
           the smallest group of bytes physically on the disk. On the  1541
           this refers to a group of 256 bytes stored together in a  single
           sector. On a PC disk, this is typically 512 bytes.

  SIGNATURE - A group of bytes, usually near or at the front of  the  file,
              which are used to identify the type of file. i.e. a PC64 file
              will always have the signature string "C64file" contained  at
              the beginning of the file.

  TAR - An acronym for "Tape ARchiver", a UNIX application, and  method  of
        backing up information.

