pppoe rate limit question

hi all
i am new to mikrotik and i set up a pppoe server on it and i want to know
about rate limit it;s in bits or bytes or what and if i want to set
64 up and 256 down for client what i put in ratelimit ?
and thanks

‘rate-limit=64k/256k’.

There are also available additional parameters with rate-limit
rate-limit=rx-rate[/tx-rate] [rx-burst-rate[/tx-burst-rate] [rx-burst-threshold[/tx-burst-threshold] [rx-burst-time[/tx-burst-time] [priority] [rx-rate-min[/tx-rate-min]]]]