Swap space or page file is reserved on the:

The motherboard provides bus and chipset infrastructure but contains no persistent storage medium where virtual memory pages can be written or reserved.

Swap space supplements physical memory (RAM) precisely because RAM is full - it is stored on disk, not within the memory modules themselves.

The operating system reserves a dedicated region on the hard disk for virtual memory - called swap space in Linux/Unix environments and a page file in Windows. When physical RAM is exhausted, the OS moves inactive memory pages to this disk-based area, freeing RAM for active processes. This disk-resident virtual memory is a foundational OS memory management mechanism distinct from physical RAM.

The CPU contains registers and cache for active computation but has no persistent storage capacity for virtual memory page storage.