1. A data transfer method for a computer system in which a computer is logically divided into a plurality of logical processing units and a logical coupling unit, the method comprising the steps of: previously storing address translation information indicating a correspondence between each of said plurality of logical processing units and a location of a memory allocated to each of said plurality of logical processing units in a memory of said computer; issuing a write command from a first logical processing unit among said plurality of said logical processing units to said coupling unit, said write command including a data/pointer flag that indicates whether information to be transferred to a second logical processing unit, which is one of said plurality of logical processing units other than said first logical processing unit, is data to be transferred to said second logical processing unit or pointer information which is used to obtain a location of the memory in which the data to be transferred is stored; transferring said information to be transferred to said coupling unit; in response to said write command issued from said first logical processing unit, storing, by said coupling unit, said information to be transferred and said data/pointer flag into a data transfer area of said coupling unit; in response to a read command issued from said second logical processing unit, transferring said information to be transferred and said data/pointer flag from said logical coupling unit to said second logical processing unit; determining, by said second logical processing unit, whether said information to be transferred is data to be transferred or pointer information in accordance with said data/pointer flag; calculating, if said data/pointer flag indicates that said information to be transferred is pointer information, a physical address to which the data to be transferred is stored on the basis of said pointer information and said address translation information; and reading the data to be transferred at said second logical processing unit by using the calculated physical address.