Type of SSL connection used when visiting google services

I have 2 computers running chrome: a) Win 8 , latest chrome b) Win 7 , latest chrome ~ 1.5 yr old high spec laptop

Both display the Certificate Authority as: Google Internet Authority G2

computer a) uses 256-bit, CHACHA20_POLY1305 with ECDHE_ECDSA for key exchange

computer b) uses 128-bit, AES_128_GCM with ECDHE_ECDSA for key exchange

This applies when I visit youtube, and google.

I am wondering why might computer b) be using a lesser type of encryption for googles services?

Thanks for any insight