|uint8_t||8 bits||1 byte|
|uint16_t||16 bits||2 bytes|
|uint32_t||32 bits||4 bytes|
|uint64_t||64 bits||8 bytes|
The fixed types uint8_t, uint16_t, uint32_t and uint64_t are equal respectively to (in most cases depending on the platform & compiler): unsigned char, unsigned short, unsigned int and unsigned long long.
The fixed types were introduced to be just that, fixed types independent of the platform.