Understanding voxel unit

Please look for basic information of byte or bit on the web.
Explain gray data, not describe color data at here.

The minimum voxel unit of digital data is 1 byte.
1 byte is 8 bits, its range in 2⁸=256
In computer world, 0 is counted so expressed range is 0~255, not 1~256
Most of data have 8 bits (1 byte), 16 bits (2 bytes) or 32 bits (4 bytes) unit
You will see the word "unsigned" or "signed" often.
unsigned 8 bits data has positive range (0 ~ 255)
signed 8 bits data has positive and nagative range (-128 ~ 127)
unsigned 8 bits or unsigned 16 bits is used often.

Each voxel has gray value and suppose data is unsigned 8 bits
0 is black, getting brighter as gray value goes higher, 255 is white
If unit is 2 bytes long and unsigned, unsigned 16 bits = 2¹⁶=65536=0~65535
Gradient steps can be divied by 65536
It can be divided by in details compares to 1 byte which has only 256 steps but data became bigger.
Basically volume data is big and processing speed defers by size
If it is too heavy, can not be loaded on computer memory or take a long to load.
(ex) data size: 2000 x 2000 x 3000
2000 x 2000 x 3000 x 1 byte = 12,000,000,000 = 12GB
2000 x 2000 x 3000 x 2 byte = 24,000,000,000 = 24GB (big data!)