Tweak fileformat.txt.

1 files changed, 12 insertions, 5 deletions

diff --git a/doc/fileformat.txt b/doc/fileformat.txt
index 3638241..c0fe23c 100644
--- a/doc/fileformat.txt
+++ b/doc/fileformat.txt
@@ -38,13 +38,20 @@ Other things caused by the limitations of the Atari:
   the filename terminator, and any remaining bytes in the field
   will be set to $20 (ASCII spaces, *not* more nulls).
 
+- Atari filenames with no extensions (e.g. "FOO") are stored with
+  a trailing period (e.g. "FOO.") in the ALF header. Upon extraction,
+  Atari DOSes will remove the period, so the file will be called
+  "FOO" again. I'm not sure whether the ARC for the Atari shares this
+  behavious, but ARC on MS-DOS or Linux doesn't do this.
+
 - ALF files are never embedded inside a self-extracting executable,
   so the first file's header always starts at the first byte of
   the file.
 
 - ARC and ALF both store the compressed and uncompressed file lengths
-  as 32-bit unsigned integers... but for ALF, the maximum file size
-  that can be compressed is probably under 64KB, so both the lengths
-  should have their last 2 bytes set fo 0. I haven't yet attempted
-  to compress a file larger than 64KB with ALF on the Atari, so I
-  may be wrong...
+  as 32-bit unsigned integers... but the Atari can't deal with really
+  large files. From examining the disassembled code of UNALF14.COM,
+  it looks like the highest byte isn't even looked at, meaning the
+  maximum size for a single file is 16MB. I have actually tested the
+  Atari ALF and UNALF programs with an emulator (and emulated hard
+  drive) with a file of 200KB in size, and it worked fine.