The so-called cash is foreign paper money. Because China has no obligation to circulate in China for foreign governments, it cannot be used in China. After receiving foreign currencies, Chinese banks collect them by currency, transport them to different countries and deposit them in their banks, thus generating interest income. During the period of waiting for concentration, sorting, storage, storage costs, transportation losses, insurance premiums, interest, etc. in the whole process will generate a lot of expenses, which will eventually be reflected in the so-called difference between cash and cash. What I said above is the process of recording cash, that is, the process of changing cash into cash. Cash is the foreign currency remitted to you directly by your relatives and friends from abroad, which stays on the books and you never take it out of the bank. From the bank's point of view, the money still exists in foreign banks, the nominal depositor is the remittance bank, and the remittance bank is recorded in your name. If you use the money, the bank can call it out or take it away by telegram. This is cash. As can be seen from the above, cash remittance is much more convenient than cash, and the cost is much less. If you invest in foreign exchange, of course, you have to change your money into cash, not cash.