BBC BASIC contained aliases for the commonly used VDU codes (such as GCOL for VDU 18 or PLOT for VDU 25). Some statements were direct equivalents to VDU codes, such as CLS for VDU 12. Some statements were less exact equivalents as they incorporated functionality specific to BASIC as well as calling the OS routines; for example the statement would set screen mode and adjust the BASIC system variable HIMEM according to the amount of memory the new mode left available for BASIC, while would set the screen mode only, without altering HIMEM. This allowed a programmer to allocate a block of memory from BASIC for example to load machine code routines into by lowering the value of HIMEM at the start of a program, and still be free to switch screen modes without deallocating it as a side effect.