Question

Answer all elaborately or dont even attempt.

7. (4 points) Explain why, in MARIE, the MAR is only 12 bits wide while the AC is 16 bits wide. Hint: Consider the difference between data and addresses. 8. (24 points) Use a few sentences to answer each of the following questions. The answers can be found in section 4.1 to 4.7 in the textbook. 1) What purpose does the datapath in a CPU serve? 2) What does the control unit in a CPU do? 3) Where are registers located? 4) How does the ALU know which function to perform? 5) Explain the differences between data buses, address buses, and control buses. 6) Explain the relation between clock cycle time and clock frequency. 7) Explain the differences between memory-mapped I/O and instruction-based I/O. 8) Explain the differences between byte addressable and word addressable. 9. (6 points) Write the assembly language equivalent of the following MARIE machine language instructions: a) 0111 0000 0000 0000 b) 1011 0011 0011 0000 c) 0100 1111 0100 1111

Answer 1

7) MARIE can handle 16-bit data, so the AC must be 16 bits wide. However, MARIE's memory is limited to 4096 address locations, so the MAR only needs to be 12 bits wide to hold the largest address.

8)

1)Datapath is the path that the input data follows in a processor to appear as an output . It is made up of the functional units that handle data in an order relative to each other. Typically, in a microprocessor, the units in atleast one of the datapaths would be: instruction registers, decode latch, ALU registers, load store unit, writeback unit and the memory.

2) The control unit (CU) is a component of a computer's central processing unit (CPU) that directs the operation of the processor. It tells the computer's memory, arithmetic and logic unit and input and output devices how to respond to the instructions that have been sent to the processor.

3) Processor registers are normally at the top of the memory hierarchy, and provide the fastest way to access data. The term normally refers only to the group of registers that are directly encoded as part of an instruction, as defined by the instruction set

4)The control unit tells the ALU what operation to perform on that data, and the ALU stores the result in an output register. The control unit moves the data between these registers, the ALU, and memory.

5)

Address Bus	Control Bus	Data Bus
Definition
It is the connections between CPU and main memory.	It is the physical connection between CPU and other devices with the computer.	It is a communication route through which data can travel between the computer’s CPU, memory, and peripherals.
Purpose
It is used to identify particular locations in main memory where data is stored.	It carriers control information between the CPU and other devices within the computer.	Data can travel through the data bus between the computer’s CPU, memory, and peripherals.
Working example
The number of bits in the address bus can determine the amount of memory, the CPU can address.in modern PCs, there are 36 address lines to access the 64 GB of main memory theoretically.	One line of the bus is used to indicate whether the CPU is currently reading from or writing to main memory.	The number of wires determines the speed of data traveling. Each wire transmits a single bit at a time. So 8 bits bus can transfer 8 bits at a time.

6) Clock frequency is the reciprocal of cycle time and vice versa.

8)

BYTE ADDRESSABLE MEMORY	WORD ADDRESSABLE MEMORY
When the data space in the cell = 8 bits then the corresponding address space is called as Byte Address.	When the data space in the cell = word length of CPU then the corresponding address space is called as Word Address.
Based on this data storage i.e. Bytewise storage, the memory chip configuration is named as Byte Addressable Memory.	Based on this data storage i.e. Wordwise storage, the memory chip configuration is named as Word Addressable Memory.
For eg. : 64K X 8 chip has 16 bit Address and cell size = 8 bits (1 Byte) which means that in this chip, data is stored byte by byte.	For eg. : For a 16-bit CPU, 64K X 16 chip has 16 bit Address & cell size = 16 bits (Word Length of CPU) which means that in this chip, data is stored word by word.