help me answer number 4,5,6

4. (a) Use a block diagram, shown how 64kx1 dynamic RAMs can be expanded to build a 256kx4 RAM. (b) Explain the flash memory. (10%) 5. (a) If the computer has 32 data registers (R0 to R31), 2000 words in memory, and 16 different instructions. What is the minimum size of an add instruction in bits if a typical instruction use the following format: add RO R2 (b) A microprocessor has the following instruction. ADD Rd, Rs1, Rs2. Where Rd is the output destination register and Rs1, Rs2 are two input source registers. Is the Microprocessor a RISC or a CISC? Please give your reasons. (10%) 6. (a) Compare polled I/O, interrupt-driven, and 1/0 DMA (b) Please explain the differences between isolated I/O method and memory-mapped 1/0 method. (10%)