Running like a dog meaning

: Re the phrase - "my computer is 'running like a dog'". I understand this to mean that my computer is running very slowly. Anything that is 'running like a dog' means it is slow. But to 'run like a dog' infers to run fast. Where did the phrase 'running like a dog' come from, as it appears illogical? Dogs run very fast :)

Here's one possible origin. I searched "horsing racing" and "running like a dog" and found this: To be successful in keeping the horse off the inside leg, to stop it dropping the shoulder, bulging the rear end into the circle and flying above the bit is to fix the canter. For the horse to experience a comfortable canter, rather than running like a dog, is to put belief into the mind and therefore eliminate the tension.