If bits are continuous how can computers tell them apart?

Question

If bits are just a signal that switches from being on to being off, how does a computer know to interpret how many bits are being represented by each switch? Like, for example, how does a computer know a message is 0100011001 instead of just 010101. Also, if a message starts with a 0, how does a computer know to include in the message? Also, how does a computer know when one message ends and another begins?

In: Technology

Answer 1

There are several ways this is done

One way is to expand the signal so you can’t have a load of zeros in a row. A simple way is to make 0 = 01 and 1 = 10

So 0100011001 becomes 01100101011010010110 on the actual wire. The computer can see the gap between 101 is shorter than 1001 and so know there is 0 in there rather than 00.

Another way is to have a 2nd wire with a synchronization pulse, so your example becomes 2 signals that go

1010101010
0100011001

The computer can use that top signal that always changes to know what bit it is at on the bottom signal.

To know when to start a message and what message it’s on, it might always send a 1 as the first bit of any message, followed by data that indicates what the message is, finally followed by the actual message.