another program starting at line 200, etc. Valid line numbers in most models were from 1 to 999. To prevent run-on execution, each program had to finish with the END command, unless run-on execution was desired. On Sharp-derived units, labels could be inserted into the program, usually single characters such that in Run mode, that program could be executed by depressing a special DEF key followed by the key of that character. This was equivalent to an explicit GOTO command to the first line number of that section of program, which was also a valid way to execute programs from Run mode. In the Casio-derived models, the BASIC space was subdivided into segmented program spaces which could be numbered, cleared and executed manually, or could call each other. Many of the devices included a special modifier key to expedite the entry of BASIC commands as well as scientific function names. The most common commands would each be associated with a key, and the full command could be entered by depressing the special modifier key, followed by the associated key for the command. In some models, BASIC and other commands would be converted into one-character tokens (converted to strings upon display) instead of being stored as whole strings. Memory The total memory capacity of the devices varied from 1 KB to 12 KB and up as far as 16 KB with the use of an available RAM card (only for some models). The optional RAM cards varied in sizes from 1 KB, 4 KB and 8 KB. All user storage was taken from the same space, so allocation of arrays using DIM would decrease the available memory for program instructions, and vice versa. However, the storage space for one-character alphabetical variables was pre-allocated, and as a result the A array had special significance in many units. For example, in the PC-8, the A array actually pointed to the locations of the alphabetical variables, so A(2) pointed to the value of B, and so on. As a result, published programs for the device avoided the use of A as either an array or an alphabetical variable. On some models the entire variable space could be manipulated in this fashion. Other notes It was not possible to define new mathematical function commands for use in Run mode. However, on many Sharp derived models, a special AREAD command was added to BASIC which would