Just curious of the following example from the documentation. How to related the digit 8 in uint8 and 32 bytes? Thanks in advance.

The following array occupies 32 bytes (1 slot) in storage, but 128 bytes (4 items with 32 bytes each) in memory.

uint8[4] a;

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The number of the uintX type is in bits (as this is common for number representation in many languages). Therefore a uint that uses the full width (32 bytes) available in Solidity would be a uint256.

In general you have the following conversion: 1 slot = 1 word = 32 bytes = 256 bits

Regarding the storage and memory related part: In memory Solidity always pads all values to 32 bytes, therefore an uint8 will use the same memory as a uint256, but in storage Solidity optimized the usage, to avoid additional gas costs, therefore it only uses the minimal storage required. In case of a uint8 this would be 1 bytes. Therefore you can store up to 32 uint8 in one storage slot (see conversions above)

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