Some articles were going on about the 5000 day mark met yesterday on the media, considering the number of days since the Bitcoin Network mine the genesis block on the 03/01/2009.
As far as I know the Bitcoin software was not released at that time and the network hadn't started yet. It all started 6 days later with block #1 on 2009-01-09.
In 2010~
Then, fast forwarding to 2013,~
Can we even count chain reorgs due to some software versions being buggy as "downtime"? The network didn't go down, the chain was still growing specially in the second case and miners kept mining.