Hi,
See this wiki: http://processors.wiki.ti.com/index.php/Sitara_Uniflash_Quick_Start_Guide#Overview :
"Uniflash is one part of an overall system that includes the Windows PC on which Uniflash runs, a target board including an AM335x Sitara Processor and flash memory to be programmed, and a USB or Ethernet connection between the two. It is assumed that the flash on the target board is blank, or needs to be overwritten. Therefore, the target board has nothing that it can execute except the bootloader stored in ROM. So the ROM bootloader will use either USB or Ethernet to request files served by Uniflash on the Host PC and once transferred, executed on the target board."