Chapter 1: Microprocessor Design

Question 1

What is a microprocessor ? (Definition)

Answer 1

A microprocessor is a programmable device that takes inputs, processes them according to a set of instructions that are stored in memory and then produces outputs. It is the heart of any computing system.

Question 2

What is a microprocessor responsible for?

Answer 2

1) Getting data or information from system inputs
2) Storing that information in the system memory
3) Manipulating the information
4) Sending the results of the manipulation to the system memory or an output

Question 3

What is the main component of a microprocessor?

Answer 3

Silicon-based transistors used to create digital logic circuits.

Question 4

What is an Arithmetic Logic Unit?

Answer 4

Combined circuitry that can perform mathematical functions on two inputs with a third input determining what type of process should be done; addition, subtraction or comparison.

Question 5

What does VLSI stand for? What is it?

Answer 5

Very-large-scale-integration is the process of combining different gates (millions or billions of transistors) onto a single chip, a piece of semiconductor.

Question 6

What digital blocks / components does a microprocessor contain?

Answer 6

1) Arithmetic Logic Unit (ALU)
2) Registers
3) Memory arrays (can be on-chip or off-chip) : RAM & ROM
4) Control Unit / counter

Question 7

What defines the architecture of a microprocessor?

Answer 7

1) The instruction set – a set of commands like a programming language. They tend to be very basic commands such as add or subtract or jump.
2) Locations of memory containing data.
We use this information to enable the computer to do different tasks.

Question 8

What architecture is most commonly used in personal computers? Who developed it? When was it first introduced?

Answer 8

X86, developed by Intel, introduced in 1978

Question 9

Which architecture did Apple computers use before 2005/2006? Who developed it?

Answer 9

PowerPC, developed by Motorola and IBM.

Question 10

Which architecture is primarily used in mobile phones and why? Name 2 companies that use it.

Answer 10

ARM because it uses less power and produces less heat.
Used by Apple and Samsung.

Question 11

Which gaming consoles have used the MIPS architecture?

Answer 11

Sony’s PlayStation products.

Question 12

Who developed the SPARC architecture?

Answer 12

Sun Microsystems

Question 13

Why is it beneficial to have the same architecture on different hardware? Give an example.

Answer 13

It allows you to use the same programs, like Word or PowerPoint, across various devices.
Both Intel and AMD produce chips with the x86 architecture.

Question 14

What is a microcontroller? What does it consist of?

Answer 14

A microcontroller consists of a microprocessor and other essential items such as memory, a clock signal, and other peripheral devices on a single piece of silicon. This allows them to be embedded into systems out of sight of the user.

Question 15

What is machine language?

Answer 15

Instructions encoded into a number of binary digits (bits)

Question 16

What is assembly language?

Answer 16

Decoded machine instructions (machine language) into mnemonics that are easy to remember.

Question 17

What does an instruction describe?

Answer 17

An instruction describes an action (e.g. ‘move some data’, ‘add some data together’) along with the address where the data can be found.
The action is called the opcode, whilst the address(s) are called the operand.

Question 18

What is CISC and why was it developed?

Answer 18

CISC: Complex Instruction Set Computer
It was developed to enable more powerful programs with complex instructions, similar to creating reusable functions in code.

Question 19

What are the main challenges of CISC design?

Answer 19

Low power operations: the hardware needs to be able to handle lots of instructions (often consisting of variable numbers of bits) which is harder to design.
Speed optimization: some of these instructions take longer to carry out than others.

Question 20

What is an example of a CISC architecture ?

Answer 20

x86 architecture used in Intel and AMD chips.
This architecture retains old instructions to prioritize software compatibility over technical simplicity so that old algorithms still work.

Question 21

What is RISC architecture? What is its main advantage?

Answer 21

RISC: Reduced Instruction Set Computer
Optimized speed: RISC uses a small, fixed set of basic instructions

Question 22

How are RISC instructions encoded and why?

Answer 22

All instructions are encoded in the same number of bits with a well-defined format. This ensures each instruction takes the same time to complete and makes them easier to decode in the hardware.

Question 23

How does RISC handle complex operations?

Answer 23

More-complicated instructions (e.g reading and writing to external memory) are broken down into simpler functions (e.g. load and store), using the faster registers for temporary storage of data.

Question 24

What is a potential risk as RISC evolves? Give an example

Answer 24

The danger with RISC architectures is that as more instructions are added, they evolve and transform into a CISC architecture.
ARM : RISC architecture initially had 46 instructions but recently the latest processor has several hundred.

Question 25

What is a word in computer architecture?

Answer 25

A word is a fixed-sized group of bits handled as a unit by the microprocessor.
Its length varies by architecture.

Question 26

What is non-volatile memory? What does this memory store?

Answer 26

Non-volatile memory must continue to store information when there is no power on the chip.
Used to store instructions.

Question 27

What is volatile memory?

Answer 27

Memory that requires power to maintain stored information; it is typically faster and used for data storage.

Question 28

How do instructions access a specific byte of data?

Answer 28

Each piece of data has a unique address that the instruction uses to access it.

Question 29

What is a memory map?

Answer 29

A layout showing addresses of different types of memory in a microprocessor, often given in hexadecimal.

Question 30

What does it mean to “memory map” inputs and outputs?

Answer 30

Assigning them addresses to make them appear as memory, simplifying their handling.

Question 31

What are registers?

Answer 31

Registers are the fastest type of memory and can be directly addressed by processor machine code instructions. They are used for the most immediate data access.

Question 32

What determines the speed at which a processor can execute a program?

Answer 32

The speed is mainly determined by how quickly the processor can access data.

Question 33

What is cache memory?

Answer 33

Cache: next fastest memory after registers, located close to the processor, provides quick access to frequently needed data.

Question 34

How does main memory compare to registers and cache in terms of speed?

Answer 34

Main memory is slower than registers and cache and requires a bus transaction to access, typically taking a few cycles.

Question 35

How does storage (e.g., disk, flash) compare in access speed?

Answer 35

Storage systems are the slowest type of memory, requiring multiple bus transactions and having typical access times in hundreds of cycles.

Question 36

How does a microprocessor execute instructions?

Answer 36

A microprocessor executes instructions in sequence.
Each of the instructions is stored in consecutive addresses in memory.

Question 37

What is the program counter?

Answer 37

Program counter: special register that marks the address of the current instruction being carried out and increments by one with each instruction.
You can change the linear flow of a programme by adjusting the programme counter.

Question 38

What is the programmers model? What does it include?

Answer 38

The programmers’ model is a description of the processor and enough of the rest of the system for the programmer to write software.

It includes:
- Description of all instructions: The Instruction Set
- Memory map
- Details of the registers
- Vector information, i.e. places to look for programs and when to execute them (e.g. on power-up/reset, interrupt vector)

Question 39

What is the function of the clock in a microprocessor? What does it do?

Answer 39

The clock synchronizes logic components to operate at the correct time.
It determines the speed of instruction execution, often a simple square wave with a MHz or GHz frequency.

Question 40

How does instruction execution differ in RISC vs. CISC architectures?

Answer 40

RISC executes each instruction in one clock cycle, while CISC may take multiple cycles.

Question 41

What is the Von Neumann architecture? Give an example.

Answer 41

An architecture where program instructions and data share a single memory and a single bus.
The x86 PC is an example.

Question 42

What are the advantages of the Von Neumann architecture?

Answer 42

It stores program instructions and data together, allowing the system to create or modify its own code.

Question 43

What is the main disadvantage of the Von Neumann architecture?

Answer 43

The single bus (used for both instructions and data) creates a bottleneck because instructions and data have to take turns using the same pathway, slowing down the CPUs speed.

Question 44

What is a bus?

Answer 44

Bus: digital data highway consisting of several parallel wires.

Question 45

What is a bottleneck?

Answer 45

A bottleneck is a point of congestion or limitation in a system that slows down overall performance. In computing, a bottleneck occurs when a component cannot keep up with the rest of the system, limiting the speed at which tasks can be completed.

Question 46

What is the Harvard architecture? Give an example.

Answer 46

An architecture with separate memory blocks and buses for program instructions and data.
The PIC microcontroller is an example.

Question 47

What are the advantages of the Harvard architecture?

Answer 47

It allows simultaneous access to instructions and data, making it faster, and buses can have different sizes (carry a different number of bits since data words and instructions aren’t necessarily the same size).

Question 48

What is a disadvantage of the Harvard architecture?

Answer 48

It cannot download new programs to itself.
A system with Harvard architecture cannot easily modify or add new program code directly to its instruction memory while it is running because it cannot treat instructions as modifiable data.