There are many Microchip microcontroller families.
8-bit: PIC10, PIC12, PIC16, PIC18
16bit: PIC24, PIC30, PIC33
If you go to Microchip website and enter microcontrollers (link) you will see these families on the left side.
Regarding 256 x 8 bytes - I agree that this may mislead.
256 x 8 means: 256 directly addressable 8-bit registers of memory (256*8 bits).
Each byte has separate address.
0x0000 xxxxxxxx (byte 0)
0x0001 xxxxxxxx (byte 1)
0x0002 xxxxxxxx (byte 2)
0x0003 xxxxxxxx (byte 3)
If that would be
256 x 16 - thay would be 512 bytes, but only 256 directly addressable (you have to store 16 bits at once) and you cannot directly access each byte.
0x0000 xxxxxxxx xxxxxxxx (byte 0, byte 1)
0x0001 xxxxxxxx xxxxxxxx (byte 2, byte 2)
In Intel x86 - most of registers are 32-bit wide. You cannot read only one byte, you have to read whole register to get one byte from it.