What the flash, eMMC, SDRAM, sysRAM, and IROM mean in tx2?

Is the flash external sd card? If ture, why BCT, MB1, MB2 are in flash?

Is the sysRAM the 266KB SRAM, then what is SDRAM and what its size is? What the difference between sysRAM and SDRAM? Why BCT and MB1 and some FW are loaded into sysRAM but MB2, TOS, and other FW into SDRAM?

IROM is 128 kb ROM, i.e. internal eeprom?

FYI,the attached pic. is a part of the tx2 boot flow.

Flash is just what the flash process installs. For a TX2 this is all on the eMMC. The term “flash” is unrelated to SD. I can’t answer the other questions other than to say the content is for stages of boot prior to Linux itself running.