How many years of millisecond timestamps can be represented by 41 bits?

Question

I am watching an Instagram blog post about generating pending identifiers . This blog post describes the creation of 64-bit identifiers. Their mechanism allocates 41 of the 64 bit millisecond timestamps, and they say:

• 41 bits for time in milliseconds (gives us 41 years of user era identifiers)

It's a typo? I calculated that you can store 69 years of millisecond timestamps in 41 bits. Here's how:

• Maximum milliseconds stored in 41 bits: (2 ^ 41) -1 = 2199023255551 ms
• Divided by (1000 * 60 * 60 * 24 * 365) ms / year = 69 years

So where am I wrong?

Answer 1

You were not mistaken in the calculation.

(2^41)-1 ms == 2199023255.551 s == 610839.7932086 hr == 25451.65805036 days == 69.6828 Julian years == 69.6843 Gregorian Years 

Which line is closely related to your result ( 69 years ).

However, the website you link to says 41 bits gives them

41 year user era identifiers

The “era” in this context probably refers to the start date. Given that this article was published "3 years ago" or in 2012 , we can calculate that their era begins in 2012 + 41 - 69 == 1984 . This date was selected as a link .