Encoded on measurable attributes
With fiber:
- lights off or on
- its frequency
- its intensity
- its polarity
- or combination of each compounding the data transfer rate.
It can all be normalized to the digital states of 0 and 1.
- Calculator pad to processor.
- Brute force is 13 wires. 0-9 +-=
- I wire is a bit.
- 1 bit has 2 combinations, not enough;
- 2 bits has 4 combinations, not enough;
- 3 bits have 8 combinations, not enough;
- But 4 bits has 16 combination which is enough;
- 4 bits is called a NIBBLE.
Bits represented as 0010 with one side the lsb and one side the msb. Lets say the left is the lsb.
3 + 4 = 5 0011 + 0100 = 0111
Define bases
After 9 use A-Z
- 0000 - 0
- 0001 - 1
- 0010 - 2
- 0011 - 3
- 0100 - 4
- 0101 - 5
- 0110 - 6
- 0111 - 7
- 1000 - 8
- 1001 - 9
- 1010 - A
- 1011 - B
- 1100 - C
- 1101 - D
- 1110 - E
- 1111 - F
3 + 4 = 5 But diff 3 + 9 = C And 1F + 3 = 22
Good for numbers but now we want to transfer letters. We have A/a. A nibble or 4 bits is only 16 combo so not enough. So if I put two nibbles together. 2*4 bits or 8 bits gives me 256 different combo. Enough for alphabet upper lower, numbers and some extra.
8 bits this is called a BYTE. And is the most important data unit.
Next is to have a standard map to translate between a number and a letter. ASCII is this map. Each letter or number have a value.
Now we can encode letters. Allowing us to make a printer which can print those letters back over a data line.
Chinese has way more then 256 characters so we need to introduce a new character map called Unicode. Each letter is two byte large. 2 bytes is also called a word. Possible combo is 65536. Enough for all sorts of languages.
ASCII and Unicode are basic letter encoding styles. Mostly ASCII.
Sram, static ram. is the fastest but costliest storage. There's a way I can put two logic gates that feed their outputs to each other, so that they store a bit value on or off. I can arrange these in huge fields with rows and columns like crops, and store large amounts of bits.
Dram, dynamic ram. A much smaller storage mechanism, and easier to reproduce. Allowing 1000s of times increase in storage capacity. Vast fields of draining wells. With a refresh process to check how empty and refill if partially filled. Also arranged in huge fields with rows and columns like crops, allowing the storage of vast quantities of bits.
Ddram, also called DDR or double dynamic ram. Uses the same technique as Dram but allows two reads and writes per access. The data wires to the memory chips have become the bottleneck. So DDR uses a half rise and half fall to double the bandwidth though the memory terminals. Everything else inside the package is similar to Dram.
Nvram, also called non volatile ram. Uses a floating charge inside the silicon to hold a value. Setting or clearing the charge as needed. Holds its value even when power has been removed.
Platters, spinning platters and a read/write head slide to magnetic islands on the platters changing the magnetism of that island to store a one or zero. Also holds its values when power has been removed.
used for verifying a block of data
CRC
MD5/SHA1