A 4 kilobyte (KB) byte-addressable memory is realized using four 1 KB memory blocks. Two input address lines (IA4 and IA3) are connected to the chip select (CS) port of these memory blocks through a decoder as shown in the figure. The remaining ten input address lines from IA11–IA0 are connected to the address port of these blocks. The chip select (CS) is active high. The input memory addresses (IA11–IA0), in decimal, for the starting locations (Addr=0) of each block (indicated as X1, X2, X3, X4 in the figure) are among the options given below. Which one of the following options is CORRECT?

To find the starting address in decimal for each 1 KB memory block (indicated as X1, X2, X3, X4), consider the 12-bit input address $\text{IA11}–\text{IA0}$:

1. Starting location condition: For the starting location of each memory block, the internal address is $\text{Addr} = 0$. Since the remaining 10 address lines (IA11–IA5 and IA2–IA0) form the 10-bit $\text{Addr}$ input, all these 10 lines must be $0$:

   $$\text{IA11} = \text{IA10} = \text{IA9} = \text{IA8} = \text{IA7} = \text{IA6} = \text{IA5} = 0$$

   $$\text{IA2} = \text{IA1} = \text{IA0} = 0$$

2. Decoder inputs: The 2-to-4 decoder selects the memory blocks based on lines $\text{IA4}$ (connected to $A_1$) and $\text{IA3}$ (connected to $A_0$):

   • Block X1 (selected by $Q_0$):$(A_1, A_0) = (0, 0) \implies \text{IA4} = 0, \text{IA3} = 0$

     $$\text{Address} = (0000000\;00\;000)_2 = 0$$

   • Block X2 (selected by $Q_1$):$(A_1, A_0) = (0, 1) \implies \text{IA4} = 0, \text{IA3} = 1$

     $$\text{Address} = (0000000\;01\;000)_2 = 2^3 = 8$$

   • Block X3 (selected by $Q_2$):$(A_1, A_0) = (1, 0) \implies \text{IA4} = 1, \text{IA3} = 0$

     $$\text{Address} = (0000000\;10\;000)_2 = 2^4 = 16$$

   • Block X4 (selected by $Q_3$):$(A_1, A_0) = (1, 1) \implies \text{IA4} = 1, \text{IA3} = 1$

     $$\text{Address} = (0000000\;11\;000)_2 = 2^4 + 2^3 = 24$$

Thus, the starting addresses for blocks X1, X2, X3, and X4 are $(0, 8, 16, 24)$, which corresponds to Option (C).