Why sp is 8 bit long while PC and dptr are 16 bit longs in 8051?

In the 8051 microcontroller architecture, the stack pointer (SP) is 8 bits long because it directly addresses a limited range of memory locations within the internal RAM, specifically up to 256 bytes. In contrast, the program counter (PC) and data pointer (DPTR) are 16 bits long to accommodate larger address spaces; the PC can address up to 64KB of program memory, while the DPTR can address up to 64KB of external data memory. This distinction allows for efficient use of resources while maintaining compatibility with the architecture's requirements.