[TUHS] why is sum reporting different checksum's between v6 and v7

[Will Senn]

All,

While working on the latest episode of my saga about moving files 
between v6 and v7, I noticed that the sum utility from v6 reports a 
different checksum than it does using the sum utility from v7 for the 
same file. To confirm, I did the following on both systems:

# echo "Hello, World" > hi.txt
# cat hi.txt
Hello, World

Then on v6:
# sum hi.txt
1106 1

But on v7:
# sum hi.txt
37264     1

There is no man page for the utility on v6, and it's assembler. On v7, 
there's a manpage and it's C:
man sum
...
Sum calculates and prints a 16-bit checksum for the named
      file, and also prints the number of blocks in the file.
...

A few questions:
1. I'll eventually be able to read assembly and learn what the v6 
utility is doing the hard way, but does anyone know what's going on here?
2. Why is sum reporting different checksum's between v6 and v7?
3. Do you know of an alternative to check that the bytes were 
transferred exactly? I used od and then compared the text representation 
of the bytes  on the host using diff (other than differences in output 
between v6 and v7 related to duplicate lines, it worked ok but is clunky).

Thanks,

Will