To subtract, the operator needed to know how to do complementary subtraction, which uses addition to
accomplish subtraction. Instead of offering a subtract function, the old calculator required the operator to add
the ???ten??™s complement??? of the number to be subtracted. You can search for ???ten??™s complement??? on Google to
learn more, but the point for now is that early computing devices were built for certain functions only. One could
never, for instance, use an old adding machine to maintain a list of neighbors??™ phone numbers!
The von Neumann architecture is also called the ???stored program computer.??? The program steps are stored
in the computer??™s memory, and the computation cycle of the machine retrieves the next step (instruction to be
executed) from memory, completes that computation, and then retrieves the next step. This cycle simply repeats
until the computer retrieves an instruction to ???halt.???
There are three primary units in the von Neumann computer. Memory is where both programs and data are
stored. The central processing unit (CPU) accesses the program and data in memory and performs the calculations.
The I/O unit provides access to devices for data input and output.
DATA REPRESENTATION
We??™re used to representing numbers in ???base 10.
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