If by "system unit," you mean the main part of the computer, then yes. In the past, all disk controllers were plugged into the motherboard. Nowadays, the motherboards all come with disk controllers, at least for SATA (and sometimes SAS) hard drives.
the hard disk
CPU
The external part is the part of system unit which can be seen, include the system case and the power button. And the internal part refers to the things inside the system unit example the motherboard, the expansion slot and disk driver
Sector is the smallest unit on Hard disk identified & addressed by File System.
System unit
it is part of the engine controller not a separate unit
the purpose of input unit is to input datas or information into the system
frank
The hardware unit that contains the CPU, the RAM, a hard disk, and a power supply is called the "motherboard."
Hard Drive
Base casting is mounted on the bottom of a hard drive disk unit. It is part of the intelligent circuit board that is wired there.
power supply HDD floppy disk drive