COUNTA IF Criteria Based On 2nd Column

I have a sheet with 2 columns. First Column lists sizes of Devices. Second colum lists a servername. Example:

A B
30 server_a
30 server_a
65 server_a
65 server_a
45 server_b
45 server_b
15 server_b

What I want to do is a device count, not device sum on a criteria based on Column B.

For instance whenever column B equals servername A, then count how many devices it has.

This would equal 4 instead of 190 which is the sum of the devices. I can do a sumif statement, very easily, but I don't want a sum, I just want a count.