A method of executing a Start Subchannel instruction designating an Asynchronous Data Mover subchannel and an Extended Asynchronous Data Mover operation request block, in a computing environment comprising main storage and storage class memory, said method comprising: responsive to determining that the subchannel identified by the Start Subchannel instruction is an Asynchronous Data Mover subchannel, performing: obtaining the operation request block from main storage, the operation request block comprising an address of an operation block; based on the address of the operation block, obtaining the operation block from main storage, the operation block consisting of a request block, a response block, and one or more move specification blocks (MSBs), wherein the request block comprises an MSB count field having a value indicating the number of MSBs of the operation block, wherein the response block is configured to hold exception conditions, wherein each move specification block is configured to include an operation code field, a block count field, a main storage address field, a storage class memory address field, a block size field and a flags field; for each MSB block of the operation block, obtaining (330, 332) the move specification block from the operation block, and; determining based on the flags field that the obtained move specification block is configured to obtain a list of one or more indirect data address words, wherein the main storage address field of the obtained move specification block designates an address of a first indirect data address word of the list of one or more indirect data address words, the obtained MSB specifying one or more blocks of data; for each block of data specified by the obtained MSB, obtaining from a main storage address field of an indirect data address word of the list of one or more indirect data address words a main storage address to be used in data transfer, wherein a number of blocks and a block size are determined based on the block count field and the block size field of the obtained MSB; determining based on an operation code of the operation code field in the obtained move specification block that the obtained move specification block is configured to move blocks of data; and based on the obtained move specification block, moving each block of data between the main storage and the storage class memory, wherein an address of the storage class memory used for the move is obtained using the storage class memory address field. obtaining the operation request block from main storage, the operation request block comprising an address of an operation block; based on the address of the operation block, obtaining the operation block from main storage, the operation block consisting of a request block, a response block, and one or more move specification blocks (MSBs), wherein the request block comprises an MSB count field having a value indicating the number of MSBs of the operation block, wherein the response block is configured to hold exception conditions, wherein each move specification block is configured to include an operation code field, a block count field, a main storage address field, a storage class memory address field, a block size field and a flags field; for each MSB block of the operation block, obtaining (330, 332) the move specification block from the operation block, and; determining based on the flags field that the obtained move specification block is configured to obtain a list of one or more indirect data address words, wherein the main storage address field of the obtained move specification block designates an address of a first indirect data address word of the list of one or more indirect data address words, the obtained MSB specifying one or more blocks of data; for each block of data specified by the obtained MSB, obtaining from a main storage address field of an indirect data address word of the list of one or more indirect data address words a main storage address to be used in data transfer, wherein a number of blocks and a block size are determined based on the block count field and the block size field of the obtained MSB; determining based on an operation code of the operation code field in the obtained move specification block that the obtained move specification block is configured to move blocks of data; and based on the obtained move specification block, moving each block of data between the main storage and the storage class memory, wherein an address of the storage class memory used for the move is obtained using the storage class memory address field.