It is explained well on the Wikipedia page of MINIX 3[1]:
> To achieve that, the code running in kernel must be minimal, with the file server, process server, and each device driver running as separate user-mode processes. Each driver is carefully monitored by a part of the system named the reincarnation server[2]. If a driver fails to respond to pings from this server, it is shut down and replaced by a fresh copy of the driver. In a monolithic system, a bug in a driver can easily crash the whole kernel. This is far less likely to occur in MINIX 3.
Some microkernel based systems have more monolithic designs where there's one big "most of the os" server that might be derived from a BSD or Linux kernel and the microkernel's role is more like a hypervisor.
>>It is a collection of servers that run on the Mach microkernel to implement file systems, network protocols, file access control, and other features that are implemented by the Unix kernel or similar kernels
> To achieve that, the code running in kernel must be minimal, with the file server, process server, and each device driver running as separate user-mode processes. Each driver is carefully monitored by a part of the system named the reincarnation server[2]. If a driver fails to respond to pings from this server, it is shut down and replaced by a fresh copy of the driver. In a monolithic system, a bug in a driver can easily crash the whole kernel. This is far less likely to occur in MINIX 3.
[1] https://en.wikipedia.org/wiki/Minix_3
[2] https://en.wikipedia.org/wiki/Minix_3#Reincarnate_dead_or_si...