P2 T2 L6 Computer Systems Architecture

Question 1

What is a bus? (2 points)

Answer 1

1. A Bus is a connection between different devices.

2. This connection will normally consist of multiple wires along which signals, instructions and data will be carried.

Question 2

What is the stored-program concept? (2 points)

Answer 2

1. A program must be in main memory in order for it to be executed.
2. The instructions are fetched, decoded and executed one at a time.

Question 3

Explain the concept of addressable memory (2 points)

Answer 3

1. For software programs to save and retrieve data, each unit of data must have an address where it can be individually located.
2. This memory organisation allows different programs to be stored in different parts of the main memory.

Question 4

What are the 2 types of machine architectures?
(NOTE: architecture is a set of rules and methods that describe the functionality, organization, and implementation of computer systems.)

Answer 4

The first one is called Von Neumann architecture and later Harvard architecture was adopted for designing digital computers.

1. Von Neumann architecture
2. Harvard architecture

Question 5

Explain the Von Neumann machine (2 points + 3 steps)

Answer 5

1 (point). The computer has single storage area (in memory) for storing data as well as the instruction to be executed.

2 (point). Processor needs two clock cycles to complete an instruction:

3 (step). In the first clock cycle the processor gets the instruction from memory and decodes it.

4 (step). In the next clock cycle the required data is taken from memory.

5 (step). For each instruction this cycle repeats and hence needs two cycles to complete an instruction.

Question 6

Explain the Harvard machine (3 points)

Answer 6

1. The computer has two separate memory areas for storing data and instructions.
2. Processor can complete an instruction in one cycle
3. This is faster because data can be written to memory at the same time as instructions are read from memory

Question 7

Explain the difference between von Neumann and Harvard architectures
(4 points)

Answer 7

1. Harvard architecture has separate data and instruction busses, allowing transfers to be performed simultaneously on both busses.
2. A von Neumann architecture has only one bus which is used for both data transfers and instruction fetches, and therefore data transfers and instruction fetches must be scheduled - they can not be performed at the same time.
3. The true distinction of a Harvard machine is that instruction and data memory occupy differentaddress spaces. In other words, a memory address does not uniquely identify a storage location (as it does in a Von Neumann machine); you also need to know the memory space (instruction or data) to which the address belongs.
4. In the Von Neumann Architecture, the processor requires two clock cycles to execute an instruction. While in the Harvard Architecture, the processor requires only one cycle to complete an instruction.

Question 8

Von Neumann’s principles are used in… (1 point)

Harvard principles are used in… (1 point)

Answer 8

… general purpose computers

… specialist embedded systems such as digital signal processing where speed takes priority over the complexities of design