cache line
The fixed-size chunk of memory a cache copies in and out as a unit: 64 bytes on most x86-64 and ARM64 chips, 128 bytes on Apple's M-series chips.
A cache line (block) is the unit of allocation and transfer between cache levels: an aligned block of 2^b consecutive bytes. A miss on any byte brings in the whole line; the line size is a property of the processor, readable at run time (std::hardware_destructive_interference_size is a compile-time hint).
Examples
With 64-byte lines, the addresses
0x1000to0x103Fall share one line.
See also