http://www.faq.msxnet.org/suffix.html
[.BIN]

What are the [.BIN] files?

The [.BIN] files are binary files and contain machine language. On disk, the structure is like this:
First 7 bytes of file-header:

byte 0  : ID byte #FE
byte 1+2: start-address
byte 3+4: end-address
byte 5+6: execution-address
Then follows the machine-language. Note that this is only true for BIN files on disk, because cassette-files have a separate header with the address-information in it. The structure is as follows:
First a long header with binary 1s,
10 bytes #D0 (which indicates the file type, here binary),
6 bytes for the filename, 
(a short silence),
short header with binary 1s,
2 byte start-address,
2 byte end-address,
2 byte execution-address,
then follows the machine-language.
The computer recognizes the baud rate by the long header with the binary 1's. So actually, you can save in a lot of speeds, limited by the cassette-quality (about 4600 Baud is really the maximum for good cassettes).
