Quote - 1kb = 1024 bytes (a lot of people usually just round to 1000)
and 1 MB = 1024 kb
so 80 MB would be 81,920 kilobytes, or 83,886,080 bytes.

Why 1024 and not 1000?
Because 1024 is a nice round number in binary arithmetic:-  0000 0100 0000 0000.
1000 is a very awkward number:-  0000 0011 1110 1000.

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)