8051 register banks — count of general-purpose data registers In total, how many general-purpose data registers (R0–R7 across all four register banks) are available in the 8051's internal RAM?

Introduction / Context:
The 8051 implements four banks of eight registers each, mapped in the lower internal RAM. Understanding the total number of GPRs (across banks) versus the simultaneously active set (one bank) is key for low-level programming and context switching.

Given Data / Assumptions:

• Four register banks exist in the standard 8051.
• Each bank contains R0–R7 (8 registers).
• Only one bank is active at a time, selected by PSW bits RS1:RS0.

Concept / Approach:
Total defined GPRs = number of banks * registers per bank = 4 * 8 = 32. Although only 8 are actively addressed at once, all 32 physically exist in internal RAM (addresses 00h–1Fh).

Step-by-Step Solution:

Verification / Alternative check:
Memory map shows 00h–1Fh allocated to register banks: 32 bytes total.

Why Other Options Are Wrong:

• 8: counts only one active bank.
• 16 or 64: do not match the defined four-bank structure in classic 8051.

Common Pitfalls:
Confusing the total implemented registers with the concurrently accessible bank; the PSW selects which set responds to Rn opcodes.

Final Answer:
32