[CentOS] laptop editing

How does one put centos on a laptop?
My understanding that laptops no longer come with optical drives.
Booting from an install disk would be difficult.
>From https://wiki.centos.org/HowTos/Laptops :
Preparation tasks
     Repartition your harddisk
     Backup your Master Boot Record (MBR)
     Modifying your bootloader

My understanding is that most laptops have at most one harddisk.
Can it really be unmounted for partitioning?

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Michael   hennebry at web.cs.ndsu.NoDak.edu
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