A GameShark Pro's ROM is 512kb in size.
512 split into 4 parts is 128kb.
128kb = 131072 Bytes in decimal (20000 in hex)
Full GSPro ROM 512kb =
128kb Part 1 = (1 quarter of the ROM)
128kb Part 2 = 256kb (Half the ROM)
128kb Part 3 = 384kb (3 quarters of the ROM)
128kb Part 4 = pSX Memory Card / Current V-Mem Slot
To export the Memory Card from the Full 512kb ROM using HexWorkshop:
Goto Hex Offset 60000 (From Beginning of File) for the start of the current V-Mem slot
and Select Hex Block 20000 as Size of Block to select all 128kb
Use File -> Save Selection... and add .bin to save as a pSX Emulator Memory Card