Computer System Architecture Questions and Answers

Answer: C

The buses in a computer are the data bus, which carries the data, the address bus, which carries the address of the memory location or device, and the control bus, which carries the control signals such as read, write and clock. So there are three main types of buses, option C.

Fewer than three would leave out one of these essential functions, and there is no fourth standard type of bus in the basic architecture. The answer is option C.

Answer: A

The memory data register (MDR) holds the data that is being written into memory or has just been read from it, so it acts as a buffer between the processor and the memory, and it is also called the memory buffer register (MBR). The memory address register (MAR) is a different register: it holds the address of the location being accessed. Secondary data register and primary data register are not standard names for it. The answer is option A.

Answer: B

The three types of hazards in an instruction pipeline are the structural hazard (two instructions need the same hardware resource in the same clock cycle), the data hazard (an instruction needs a result that an earlier instruction has not yet produced) and the control hazard (a branch changes the flow of the program, so the next instruction fetched may be wrong).

Address hazard and memory hazard are not standard names for pipeline hazards, so the options that contain them are wrong. The answer is option B.

Answer: B

A memory of \(N\) words needs \(n\) address bits with \(2^n \ge N\).

\[ 4096 = 2^{12} \]

So 12 address bits select any of the 4096 words. Eight bits would address only 256 words and 15 bits would address 32768 words, more than needed, and 4 bits only 16. The answer is 12, option B.

Answer: C

In a computer with a single processor register, that register holds the operand and the result of the arithmetic and logic operations, and it is usually called the accumulator (AC). A stack and a pointer are memory structures and registers for addresses, and an opcode is the operation part of an instruction, so none of them is the single working register. The answer is accumulator, option C.

Answer: C

In the basic computer architecture, the data register is a 16 bit register with the symbol DR. It holds the operand read from memory, and it feeds the ALU together with the accumulator. The address register AR has 12 bits and the program counter PC has 12 bits, but the data and the accumulator registers have 16 bits, the word length of the memory. The answer is DR, 16 bits, option C.

Answer: A

CLA is a register reference instruction of the basic computer with the hexadecimal code 7800. It clears the accumulator, setting all its bits to zero. The instruction to clear the carry bit E is CLE, with code 7400, and the complement instructions are CMA (7200) for the accumulator and CME (7100) for the carry. The answer is Clear AC, option A.

Answer: B

LDA (load accumulator) is the memory reference instruction that loads the operand from the effective address into the accumulator. STA does the opposite and stores the accumulator in memory, BUN is the branch unconditionally instruction, and BSA is the branch and save return address instruction used for subroutine calls. The answer is LDA, option B.

Answer: A

SKI is the input output instruction of the basic computer with code F200 (hexadecimal), which stands for skip on input flag: it checks the input flag FGI and, if it is set, skips the next instruction by incrementing the program counter. The skip on output flag instruction is SKO, with code F100, and ION and IOF are the instructions that turn the interrupt on and off. The answer is option A.

Answer: B

A pipeline divides an operation into segments that work on different data at the same time. The classic example of a pipeline in computer architecture is the multiply and add operation, \(A_i \times B_i + C_i\), where the first segment multiplies a pair of numbers and the next segment adds the third number, while the first segment is already working on the next pair. A single addition or a single multiplication, as in the other options, has just one step, so there is nothing to divide into stages. The answer is option B.