input: [Explanation] Central Processing Unit – the 'brain' of a computer. In the early days, these were used to hash bitcoin transactions, but are now no longer powerful enough. They are still sometimes used to hash transactions for altcoins. [Term] 
output: CPU
options: C o n f i r m a t i o n
options: C r y p t o g r a p h y
options: C i r c l e
options: C l i e n t
options: C o l o r e d c o i n s
options: C P U
options: C o i n b a s e
options: C o i n a g e
options: C r y p t o c u r r e n c y