Question About HW-frames

Hi All,
I have a some questions about wireless advanced tab as below:
1- what HW stands for???
2-what does HW-fragmentation Threshold and HW-protection Threshold? what is different between them?
3- when can i use above parameters?

Please direct me if you can. thanks in advance.

HW = HardWare

Those values are valid only for 802.11 links, they are not used neither in Nstream nor NV2.

http://wiki.mikrotik.com/wiki/Wireless_Matrix

thanks for your reply. please answer my questions:
1-what does HW-fragmentation Threshold and HW-protection Threshold? what is different between them?
2- when can i use above parameters?