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Comp Arch > Main Deck > Flashcards

Main Deck Flashcards

1
Q

Describe the Little Man computer ( what doe sit consists of?)

A

The little man Computer consists of

  • A 3 digit calculator
  • one hundred mail boxes
  • a 2 digit hand counter, with a reset button, (Instruction locations counter)
  • an “in” and “out” basket
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2
Q

What does the mailbox contents consist of? (LMC)

A

DATA ( a 3 digit number)

INSTRUCTION

  • 3|99
  • “3” is the op code, i.e what instruction to use
  • “99” is operand, refers to the address of the data value to operate on
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3
Q

What are the possible instructions used by the Little man Computer?

A 
ADD
SUB
STO
LDA
IN
OUT
COB (means stop)
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4
Q

What distinguishes a computer program from a simple calculator?

A

Instructions can be performed out of sequence, making it turing complete

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5
Q

What are the two type of branches?

A

Unconditional branching

Conditional branching

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6
Q

What are some typical things you plug into a mother board?

A

Interface card, connects to PCI
Typical magnetic hard disk
Connects to sata interface

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7
Q

What is a bus?

A

A lot of wires

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8
Q

Describe how a system runs from boot?

A
  • Processor runs boot loader instruction from ROM or NOR flash
  • These transfer OS from disk/flash/ssd into RAM and starts executing it.
  • User controls OS and can transfer EXE into RAM and run them
  • All data is sent over external buses or a bus.
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9
Q

What is a microcontroller?

A

Generally do not run operating systems, the processor directly runs the application code.

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10
Q

Why would anyone want to use a slow microcontroller without much memory?

A

Takes a sensor and can communicate with the Ci40 hub.

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11
Q

How we we get a conductive metal?

A

When metal atoms, e.g. copper, come together in solid form,
an electron from each atom can become detached and becomes free
to move around within the solid which makes it a conductor of
electricity

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12
Q

What creates a flow of electricity?

A

A sea of moving electrons exist within a piece of metal, these free electrons can be made to move by electric forces.

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13
Q

What is an insulator?

A

Substance with no free electrons and cannot pass electricity

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14
Q

What is a resistor?

A

A electrical component which are a mix of conductors and insulators, measures in Ohms

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15
Q

What is charge measured in?

A

Coulombs, 1 electron has 1.6*10^-19C

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16
Q

What is voltage?

A

The battery exert an “electromotive force” on the electrons and push them up a electric gradient, voltage refers to the distance the electron charge has been transferred.

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17
Q

Which was is current defined to flow?

A

From positive to negative(technically it is the other way)

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18
Q

What is current?

A

The rate of flow of charge

1 A is the flow of 1 C a seconf

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19
Q

What is ohms law

A

v=IR

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20
Q

What is a semiconductor and name one?

A

pure silicon doesnt have free electrons
-But DOPING it, adding small quantities of other elements can produce “free electrons” or “free holes”, it then conducts electricity well.

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21
Q

How do we make N-type silicon?

A

Add Arsenic, it has 4 covalent bonds, arsenic has 5 electrons, so a free electron is free to move around lattice, N-type refers to negative charges free to move about

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22
Q

How to we make P-type silicon?

A

Boron has 3 electrons, therefore means one adjacent electron can fill position, this makes a “moving positive hole”

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23
Q

What does a diode consist of?

A

A p-type silicon sandwiched next to a n-type silicon, current can therefor flow in one direction. E.g LED light

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24
Q

What is a capacitor?

A
  • Consists of two conductor sheets, separated by dielectric insulator
  • Stores electric charge across it when voltage is applied
  • Electric field draws positive charge towards one side, and negative charge towards other
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25
Q

Try to explain how an nMOS transistor works

A

Consists of Conductor connected to gate sitting on top of insulator sitting on top of p type substrate. When the gate is turned on the capacitor draws all the positive charge at the top of the capacitor, all the negative charge is drawn from the substrate to the bottom of the capacitor. This creates a “channel” inverting the p type to the n type, allowing negative charge to flow from source to drain. (on diagrams it is drain to source)

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26
Q

Try to explain how a pMOS tranistor works

A

Works in the opposite way to an nMOS the substrate in an n type and is connected to the VDD, when a the VDD is also supplied at the gate the n type inverts to a ptype allowing current to flow from drain to source.

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27
Q

When the gate is 0 or 1, is the nMOS on or off?

A

nMOS is ON when gate is 1 and off when gate is 0

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28
Q

When the gate is 0 or 1, is the pMOS on or off?

A

pMOS is on when the gate is 0 and off when the gate is 1

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29
Q

Draw a NOT gate CMOS

A

DRAW IT

30
Q

Draw a NAND CMOS

A

DRAW IT

31
Q

describe the CMOS 4011 chip

A

Has 4 2 input NAND gates, one NAND gate COULD be made from the CMOS NAND which consisted of 4 MOSFET transistors

32
Q

What is the general structure of CMOS

A

pMOS tranistors pull up the output voltage and nMOS transistors used to pull down the voltage

33
Q

DRAW a NOR gate CMOS

A

DRAW IT

34
Q

What is a combinational Circuit

A

The output of a combinational circuit only depends on the current inputs, so the output can be precisely described using a boolean expression

35
Q

Combinational tables can also be uniquely defined by the tables that they satisfy, how would we convert a truth table into a logic circuit.

A

Use the truth table to calculate the DNF or equivalent CNF, then convert this boolean expression into a logic circuit using the appropriate gates

36
Q

How can we prove equivalence with two boolean algebra expressions?

A

Two methods

  • Use rules of boolean algerbra (i.e axioms like 1+0 = 1)
  • De morgans theorem
  • Karnaugh Maps
37
Q

State demorgans theorem

A

¬ (a . b) = ¬a + ¬b

¬ (a + b) = ¬a . ¬b

38
Q

How can we minimise logic circuits?

A

Use boolean algebra or Karnaugh maps

39
Q

Describe how to user K maps

A

Put a truth table into a 2D matrix, we then put in DNF equivalent into matrix, ie, 1’s where combination evaluates to 1. We then circle the rectangles or squares, we then just take the factors which the shape has in common. Be aware that circles can go out one edge into the other side.

40
Q

Draw out a two input multiplexer truth table.

A 
s c d out
0 0 X 0
0 1  X  1
1  X 0 0
1  X 1   1
41
Q

What aspect must we consider with real circuits?

A

Timing, circuit can identical outputs but different implementations with therefore different behaviours.

42
Q

What causes a delay in a circuit

A

Each gate introduces a delay

43
Q

What is the critical path and shortest path in a circuit?

A

Critical path is the path of inputs which is needed for the output to be derived. Short path is the shortest path to the output.

44
Q

In terms of paths, what can lead to odd behaviour due to parallelism?

A

Both the shortest and critical path come from the same input.

45
Q

Define a glitch

A

Value should stay the same but then changes and returns to proper value

46
Q

How can we avoid a glitch using K maps?

A

Cover transition between prime implicants with another prime implicant.

47
Q

Show 2001 as a power series.

A

2.10^3 + 0.10^2 + 0.10^1 + 1. 10^0

48
Q

What is 8 in base 8?

A

10

49
Q

What happens when you multiply a number by the base

A

add a 0 to the end to it

50
Q

What is 31 base 8 in decimal

A

25 i think

51
Q

How do we convert from decimal to binary

A

Dividing the decimal number by the largest power of 2 and then successively dividing it by smaller ones

52
Q

Why do we use hex?

A

Decimal representation is fine if number has meaning, but not for computer instruction, computers don’t care about the representation, but we need a shorter representation for display/input for humans.

53
Q

How do we translate binary to hex?

A

Just convert each group of 4 bits starting from the right

54
Q

Add 345 to 273 decimal

A

do it

55
Q

What is the addition rule for a given base x

A

ri+si+ci=c(i+1)*x + ti

56
Q

What is the subtraction rule for a given base x

A

ri-si-bi = ti-b(i+1)*x

57
Q

How do we represent numbers without a negative sign?

A

Complement form

58
Q

What number does a two’s complement lead by?

A

9

59
Q

What does the ALU do?

A

takes two 4 bit numbers as input and carries out a logical operation or an arithmetic operation to produce an output

60
Q

What does a half adder do?

A

Adds one binary digit to another to get a result and also an output carry, Result is XOR and CARRY is AND

61
Q

What does a full adder do?

A

Has the carry in as a input value for the gate. Result = A XOR B XOR C, CARRY OUT = DNF of all 3

62
Q

Why should would we want to re implement a circuit using different gates?

A

Fewer gates can result in still the same truth table.
Sometimes we have preference to particular types of gates
In this case two discrete CMOS chips to form a full adder

63
Q

How do we construct a 4 bit adder?What cmos chip is this?

A

Combine 4 full adders, each carry is passed out of one adder into the next one, CMOS 4008

64
Q

How do we perform subtraction for 4 bit adder?

A

No need to create new unit, use 4 bit adder with B as 2’s complement form, 2 input multiplexers choose between normal and complement bits, 1 is added via the input carry at the top also using a multiplexer

65
Q

What is another name for the traditional 4 bit adder and why?

A

The ripple carry adder, as the carry ripples down from LSB to MSB before answer is correct and stable

66
Q

What is a downside to the ripple carry adder?

A

Can be quite slow with large calculations.

67
Q

What is the critical path in a ripple carry adder?

A

The carry propagation

68
Q

What works in parallel and in series in a ripple carry adder?

A

the adder units work in parallel and the propagation of the carry is forcing the answer to be calculated in series.

69
Q

What is the notation for a N bit adder?

A

Use the slash symbol across a wire to indicate a ‘bus’ with N number of wires

70
Q

What is a carry lookahead adder?

A

Divide the 32 bits into 4 bits with CLAs.
Instead of the carry having to propagate through each individual adder unit, the CLA has a special logic circuit which quickly calculates teh carry output based on the given inputs.
This was the carry on propagates through 8 CLA units rather than 32 adder units, making it almost 4 times as fast.

71
Q

Briefly describe the prefix adder?

A

Quickly calculates whether a carry is generated or propagates from successively larger inputs. 2 Bit, 4 bit, 8 bit, 16 bits.
Calculation is of order log2(n) due to the successive doubling block sizes considered.

Comp Arch (5 decks)

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