I'm reading about the Atlas operating system and I came across this:

The Atlas system used a British computer with 48-bit words. Addresses were 24 bits but were encoded in decimal, which allowed 1 million words to be addressed.

Why is it 1 million here if it's encoded in decimal?

  • 1
    $\begingroup$ Can you add attribution for the source where you encountered this? See our guidelines on the expectations: cs.stackexchange.com/help/referencing. Thank you! $\endgroup$
    – D.W.
    Mar 4 at 0:22

1 Answer 1


It looks like by "encoded in decimal" what they mean is binary coded decimal (BCD), which is a format which uses 4 bits to encode the numbers 0-9. Obviously this wastes a little, as those 4 bits could also encode 10-15, but that is sacrificed to make a 1:1 mapping between groups of bits and digits of a number in base 10

24-bits divided by 4 bits per base 10 digit yields 6 base 10 digits. 6 digits is enough to count from 0 to 999,999, hence a million adddresses.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.