Question 1

What is the difference between Von Neumann and Harvard architecture?

Accepted Answer

The key difference is how they handle data and instructions. Von Neumann architecture uses a single, shared memory and bus for both. Harvard architecture uses separate memories and buses for data and instructions. This allows simultaneous fetching, which can be faster, but it's more complex. Modern CPUs often use a hybrid model, with a Von Neumann main memory architecture but separate L1 caches for data and instructions (a Harvard feature).

Question 2

If I have a quad-core 3 GHz CPU, is it the same as a single-core 12 GHz CPU?

Accepted Answer

No, they are very different. A quad-core 3 GHz CPU has four processing units, each running at 3 billion cycles per second. This is excellent for multitasking or running software specifically designed for parallel processing. However, a single task that cannot be split across cores will only run on one core at 3 GHz. A hypothetical 12 GHz single-core CPU would run that same single task four times faster, but would be less efficient at multitasking.

Question 3

Why is the MDR bidirectional but the MAR is not?

Accepted Answer

The MAR's job is to specify a location in memory. The CPU only ever sends an address *to* the memory system; it never needs to read an address *from* memory. Therefore, the MAR and the address bus are unidirectional. The MDR, however, handles the actual data. It needs to receive data *from* memory (a read operation) and send data *to* memory (a write operation), so it must be bidirectional, as must the data bus.

Central Processing Unit (CPU) Architecture

What you need to know

The CPU's Grand Plan