Week 1

Question 1

How do we measure the complexity of hardware?

Answer 1

Transistors.

We measure the complexity in terms of how many transistors in a particular technology can be integrated onto a single chip of silicon (or silicon dye).

10 billion transistors on a single dye is a good idea of what it should be.

Question 2

How many lines of code do we expect a modern operating system to have?

Answer 2

10-100 million lines of code

Question 3

How many lines of code do we expect a modern operating system to have?

Answer 3

10-100 million lines of code

Question 4

The chip has 20 rectangles. 18 of them are the same, and 2 of them do something different. what are these rectangles?

Answer 4

2: memory controllers - interfacing the chip to memory outside
18: cores

Question 5

What are the four levels of abstraction, from lowest granularity to highest (where the user interacting with the software sits)?

Answer 5

1) Digital circuits (raw hardware eg wires and transistors)
2) Instruction set (low-level machine code)
3) Operating system
4) Application software

Question 6

At a high level, what is a computer?

Answer 6

A computer is a machine that has hardware that’s flexible enough to execute a sequence of instructions (a program), which direct it to operate on (process) data.

Question 7

What are 4 kinds of computers?

Answer 7

1) personal computers
2) server
3) embedded computer - a component that adds functionality to a bigger machine
4) high performance computer

Question 8

What is a concept?

Answer 8

It’s a model external to reality. Not physical. Ideas.

Question 9

What is meant by labelling?

Answer 9

Labelling implies counting, or taking a set of items and mapping these onto whole numbers e.g. Sunday = 0, Monday =1, …
These are a finite set of numbers. Such a mapping from names to numbers is called a code.

Question 10

What is measurement?

Answer 10

Measuring some physical quantity with a measuring instrument.
Result in real numbers, not integers like in labelling.

Question 11

What are the results of labelling and measurements?

Answer 11

These are data items. Data are just sequences of data items.

Question 12

Do data processing machines process data?

Answer 12

No, because machines are physical and data (being numbers) are not. We first need to find a way of representing data in physical quantities.

Question 13

What is data representation?

Answer 13

Data representation involves finding suitable physical quantities to represent numbers. We need representations that can be stored (memory) in physical devices, communicated between devices and manipulated so as to mimic abstract data operations (like addition).
Physical

Question 14

What’s a common method for data representation, ie representing intangible and abstract numbers in a physical form?

Answer 14

Voltages - easily stored and transmitted over wires.

Optic fibres.

Question 15

What are two distinct approaches to data representation?

Answer 15

Analogue representations and digital representations

Question 16

What are the limitations of data representation?

Answer 16

1) Limited accuracy
2) Noise on the environment in all situations - fluctuations that add errors to the measurement. In the case of length, a smaller tremor for example can cause an error.

Question 17

What are analogue representations?

Answer 17

It’s when we assign real numbers to continuous physical quantities. Eg x metres.

Question 18

What is a digital representation?

Answer 18

These are binary representations where there is a true/false, 0 or 1 etc.
Good because it blocks out noise errors, as for example, if we have a low voltage (0), then there’s going to have to be a substantial upward spike of noise for it to be seen as high (1).

Question 19

What is the name for a sequence of bits?

Answer 19

code word

Question 20

What is a binary code?

Answer 20

Binary code is a mapping from a data set to binary code words.

Question 21

What is a fixed length code?

Answer 21

If all the code words have the same number of bits, code is fixed length.

e.g. if letters of the alphabet all have the same number of bits

Question 22

What is a program?

Answer 22

A program is a (finite) set of instructions detailing how input data should be processed to achieve a desired result (output data)

Question 23

How can we store bits (or code words)?

Answer 23

We need a basic digital circuit that can take a bit and store it, then remember the value indefinitely, and read out the stored value. We will call them bit storage circuits.

Question 24

What is a byte?

Answer 24

A byte is a string of 8 bits.

Question 25

How many different values are there in a byte?

Answer 25

2^8 = 256 different values

Question 26

How many bits usually are there in a short word, normal sized word, and long word?

Answer 26

Short word - 16 bits (2 bytes)
Word - 32 bits (4 bytes)
Long word - 64 bits (8 bytes)

Question 27

What is a k-bit word?

Answer 27

A word that contains k bits and can represent 2^k distinct values.

Question 28

What are wires used for?

Answer 28

Connecting components, so that we can manipulate binary representations.
In electronic devices this is done by conducting wires. Each wire represents one bit at a time (as a high or low voltage between wire and ground). Multiple bits can be sent on the same wire, but not at the same time!

Question 29

In terms of wires, what is line driver/line receiver?

Answer 29

Line drivers makes the line go high or low and these are detected by the line receiver.

Question 30

What is the bit time?

Answer 30

The minimum time needed for the bit to be kept steady on the wire for it to be properly detected by the receiver.

Question 31

What is an n-bit bus?

Answer 31

An n-bit bus is n-wires running in parallel, taking 1 bit at a time.

Question 32

What are common examples of physical devices that perform operations on bits and code words?

Answer 32

Not-gate
And-gate
Or-gate
n-bit adder

Question 33

What is a transistor?

Answer 33

It’s a small electronic switch - you can switch on or off by another voltage. By sending an electronic signal, you can switch the transistor on/off. (Don’t need to know this in depth for this course).