## Integer, ASCII and Unicode

This lecture covers programming based on computation machines. Even mechanical devices allow for calculations:

So far all machines being described are based on non-semiconductor technologies. Inventing the transistor in the fifties gave rise to a rapid development of microprocessor chips:

These sample devices differ heavily with respect to addressable memory, data size, supported arithmetic operations / speed and other features. We take a closer look to Zilog's Z80 processor:

Following technological advances processors have been categorized by the length the so called address- and data-bus:

We remind the reader to the binary representation of signed integer values. Details will be discussed in your math lectures. Our first example features three bit signed integer values:

Signed byte values are being represented accordingly:

No. 11

### Hotel key cards

 Q: A hotel supplies the following type of cards for opening room doors: A customer is worried concerning the impact of loosing his card. For security reasons the corresponding pattern can never be issued again. Thus the hotel may eventually run short on available combinations. Discuss this argument by estimating the number of distinct patterns. Hint: Consider a key card's (likely?) grid of possible punch positions: A: No need to be worried: The 32 possible punch positions may be arranged in a linear fashion: Since each position may either contain a hole or be solid we have $2 32 = 4.294.967.296$ distinct possibilities. Thus a lot of key cards may get lost before a hotel manager needs to start worrying.