A method for executing a machine instruction in a central processing unit comprising steps of: obtaining, by a processor, a machine instruction for execution, the machine instruction being defined for computer execution according to a computer architecture, the machine instruction comprising: at least one opcode field to provide an opcode, the opcode identifying a load to block boundary operation; a register field to be used to designate a register, the register comprising a first operand; at least one field for locating a second operand in main memory; and a block boundary type indicator to indicate a specified type of block boundary of the second operand; and executing the machine instruction, the execution comprising: only loading bytes of the first operand with corresponding bytes of the second operand that are within a block of main memory, a boundary of the block of main memory being dynamically determined based on the specified type of block boundary and one or more characteristics of the processor, wherein the only loading comprises loading from a block of the second operand a variable amount of data into the first operand while ensuring only data within the block of the second operand is being loaded into the first operand, wherein the loading from the block of the second operand starts at a starting address in the block of the second operand, the starting address provided by the machine instruction, and wherein the loading ends at or before a determined block boundary of the block of the second operand, wherein the variable amount of data loaded is based on the starting address and the determined block boundary, the determined block boundary dynamically determined based on the specified type of block boundary and one or more characteristics of the processor, and wherein the variable amount of data is a minimum of a number of bytes in the first operand or a number of bytes loaded up to the determined block boundary. obtaining, by a processor, a machine instruction for execution, the machine instruction being defined for computer execution according to a computer architecture, the machine instruction comprising: at least one opcode field to provide an opcode, the opcode identifying a load to block boundary operation; a register field to be used to designate a register, the register comprising a first operand; at least one field for locating a second operand in main memory; and a block boundary type indicator to indicate a specified type of block boundary of the second operand; and executing the machine instruction, the execution comprising: only loading bytes of the first operand with corresponding bytes of the second operand that are within a block of main memory, a boundary of the block of main memory being dynamically determined based on the specified type of block boundary and one or more characteristics of the processor, wherein the only loading comprises loading from a block of the second operand a variable amount of data into the first operand while ensuring only data within the block of the second operand is being loaded into the first operand, wherein the loading from the block of the second operand starts at a starting address in the block of the second operand, the starting address provided by the machine instruction, and wherein the loading ends at or before a determined block boundary of the block of the second operand, wherein the variable amount of data loaded is based on the starting address and the determined block boundary, the determined block boundary dynamically determined based on the specified type of block boundary and one or more characteristics of the processor, and wherein the variable amount of data is a minimum of a number of bytes in the first operand or a number of bytes loaded up to the determined block boundary.