Why does the service (memcached) need two files /etc/init.d/memcached and /lib/systemd/system/memcached.service?

Question

linux

Hello.
For example, I took the memcached package from 18.04 - https://packages.ubuntu.com/bionic/memcached ( security.ubuntu.com/ubuntu/pool/main/m/memcached/m... )
and noticed that there are two files responsible for starting/stopping the service

/etc/init.d/memcached
/lib/systemd/system/memcached.service

The question arose: why two, why it was impossible to make only one?
Or do they have different functionality? Thank you.

Answer 1

The first is for init.d the second is for system.d, different distributions will have only one of them