Date   : Wed, 02 Mar 1983 00:35:00 EST
From   : Keith Petersen <W8SDZ@mit-mc.arpa>
Subject: FTPing COM files from the MIT-MC CPM directory

Date: 2 March 1983 00:17 EST
From: Gail Zacharias <GZ>
To:   bridger at RAND-UNIX
cc:   FJW, W8SDZ
Re:   [W8SDZ: [bridger: squeezing MC CPM files-HEXIFY]]

The HEXIFY source is on MC in AR4:GZ;HEXIFY MIDAS.  I doubt it will
do you any good.

COM files are stored on ITS as four 8-bit bytes per PDP-10 word, left
justified.  The first word is a file-type identifier and it is 446353300000
octal.  This particular packing of 8 bit bytes into pdp-10 words is pretty
standard, so if your FTP has a binary mode, it will probably do the right
thing, i.e. give you the correct sequence of 8-bit bytes coming out of the FTP.
If that is the case, the first 4 bytes should be: 223, 072, 330, 0 (octal).
These come from the id word above and are not part of the com file proper, i.e.
should be discarded before downloading to a CP/M system.

Now, if you don't have binary mode in your FTP, or if the binary mode is such
that you get something other 223,072,330,0 as first four bytes when FTPing COM
files (meaning that the server is using some other byte packing), it might
still be possible to FTP the files and reconstruct the original from that.
(The only problem might be CRLF vs. LF transformations in ascii mode).  All you
need to do figure out how the server unpacks the bytes and then "undo" it.  I'd
be happy to help out if you have trouble figuring this out.  Just let me know
what the first few bytes are when you FTP a com file.  But before you go
writing any code, make sure there is no way to make FTP win directly.