Top 50 Interview Questions

Review these typical interview questions and think about how you would answer them. Read
the questions listed; you will also find some strategy suggestions with it.

1. Tell me about yourself:
The most often asked question in interviews. You need to have a short statement prepared
in your mind. Be careful that it does not sound rehearsed. Limit it to work-related items
unless instructed otherwise. Talk about things you have done and jobs you have held that
relate to the position you are interviewing for. Start with the item farthest back and work up
to the present.

2. Why did you leave your last job?
Stay positive regardless of the circumstances. Never refer to a major problem with
management and never speak ill of supervisors, co-workers or the organization. If you do,
you will be the one looking bad. Keep smiling and talk about leaving for a positive reason
such as an opportunity, a chance to do something special or other forward-looking reasons.

3. What experience do you have in this field?
Speak about specifics that relate to the position you are applying for. If you do not have
specific experience, get as close as you can.

4. Do you consider yourself successful?
You should always answer yes and briefly explain why. A good explanation is that you have
set goals, and you have met some and are on track to achieve the others.

5. What do co-workers say about you?
Be prepared with a quote or two from co-workers. Either a specific statement or a
paraphrase will work. Jill Clark, a co-worker at Smith Company, always said I was the
hardest workers she had ever known. It is as powerful as Jill having said it at the interview
herself.

6. What do you know about this organization?
This question is one reason to do some research on the organization before the interview.
Find out where they have been and where they are going. What are the current issues and
who are the major players?

7. What have you done to improve your knowledge in the last year?
Try to include improvement activities that relate to the job. A wide variety of activities can
be mentioned as positive self-improvement. Have some good ones handy to mention.

8. Are you applying for other jobs?
Be honest but do not spend a lot of time in this area. Keep the focus on this job and what
you can do for this organization. Anything else is a distraction.

9. Why do you want to work for this organization?
This may take some thought and certainly, should be based on the research you have done
on the organization. Sincerity is extremely important here and will easily be sensed. Relate
it to your long-term career goals.

10. Do you know anyone who works for us?
Be aware of the policy on relatives working for the organization. This can affect your answer
even though they asked about friends not relatives. Be careful to mention a friend only if
they are well thought of.

11. What kind of salary do you need?
A loaded question. A nasty little game that you will probably lose if you answer first. So, do
not answer it. Instead, say something like, That's a tough question. Can you tell me the
range for this position? In most cases, the interviewer, taken off guard, will tell you. If not,
say that it can depend on the details of the job. Then give a wide range.

12. Are you a team player?
You are, of course, a team player. Be sure to have examples ready. Specifics that show you
often perform for the good of the team rather than for yourself are good evidence of your
team attitude. Do not brag, just say it in a matter-of-fact tone. This is a key point.

13. How long would you expect to work for us if hired?
Specifics here are not good. Something like this should work: I'd like it to be a long time. Or
As long as we both feel I'm doing a good job.

14. Have you ever had to fire anyone? How did you feel about that?
This is serious. Do not make light of it or in any way seem like you like to fire people. At the
same time, you will do it when it is the right thing to do. When it comes to the organization
versus the individual who has created a harmful situation, you will protect the organization.
Remember firing is not the same as layoff or reduction in force.

15. What is your philosophy towards work?
The interviewer is not looking for a long or flowery dissertation here. Do you have strong
feelings that the job gets done? Yes. That's the type of answer that works best here. Short
and positive, showing a benefit to the organization.

16. If you had enough money to retire right now, would you?
Answer yes if you would. But since you need to work, this is the type of work you prefer. Do
not say yes if you do not mean it.

17. Have you ever been asked to leave a position?
If you have not, say no. If you have, be honest, brief and avoid saying negative things
about the people or organization involved.

18. Explain how you would be an asset to this organization
You should be anxious for this question. It gives you a chance to highlight your best points
as they relate to the position being discussed. Give a little advance thought to this
relationship.

19. Why should we hire you?
Point out how your assets meet what the organization needs. Do not mention any other
candidates to make a comparison.

20. Tell me about a suggestion you have made
Have a good one ready. Be sure and use a suggestion that was accepted and was then
considered successful. One related to the type of work applied for is a real plus.

21. What irritates you about co-workers?
This is a trap question. Think real hard but fail to come up with anything that irritates you.
A short statement that you seem to get along with folks is great.

22. What is your greatest strength?
Numerous answers are good, just stay positive. A few good examples:
Your ability to prioritize, Your problem-solving skills, Your ability to work under pressure,
Your ability to focus on projects, Your professional expertise, Your leadership skills, Your
positive attitude .

23. Tell me about your dream job.
Stay away from a specific job. You cannot win. If you say the job you are contending for is it, you strain credibility. If you say another job is it, you plant the suspicion that you will be dissatisfied with this position if hired. The best is to stay genetic and say something like:
A job where I love the work, like the people, can contribute and can't wait to get to work.

24. Why do you think you would do well at this job?
Give several reasons and include skills, experience and interest.

25. What are you looking for in a job?
See answer # 23

26. What kind of person would you refuse to work with?
Do not be trivial. It would take disloyalty to the organization, violence or lawbreaking to get
you to object. Minor objections will label you as a whiner.

27. What is more important to you: the money or the work?
Money is always important, but the work is the most important. There is no better answer.

28. What would your previous supervisor say your strongest point is?
There are numerous good possibilities:
Loyalty, Energy, Positive attitude, Leadership, Team player, Expertise, Initiative, Patience,
Hard work, Creativity, Problem solver

29. Tell me about a problem you had with a supervisor
Biggest trap of all. This is a test to see if you will speak ill of your boss. If you fall for it and
tell about a problem with a former boss, you may well below the interview right there. Stay
positive and develop a poor memory about any trouble with a supervisor.

30. What has disappointed you about a job?
Don't get trivial or negative. Safe areas are few but can include:
Not enough of a challenge. You were laid off in a reduction Company did not win a contract,
which would have given you more responsibility.

31. Tell me about your ability to work under pressure.
You may say that you thrive under certain types of pressure. Give an example that relates
to the type of position applied for.

32. Do your skills match this job or another job more closely?
Probably this one. Do not give fuel to the suspicion that you may want another job more
than this one.

33. What motivates you to do your best on the job?
This is a personal trait that only you can say, but good examples are:
Challenge, Achievement, Recognition

34. Are you willing to work overtime? Nights? Weekends?
This is up to you. Be totally honest.

35. How would you know you were successful on this job?
Several ways are good measures:
You set high standards for yourself and meet them. Your outcomes are a success.Your boss
tell you that you are successful

36. Would you be willing to relocate if required?
You should be clear on this with your family prior to the interview if you think there is a
chance it may come up. Do not say yes just to get the job if the real answer is no. This can
create a lot of problems later on in your career. Be honest at this point and save yourself
future grief.

37. Are you willing to put the interests of the organization ahead of your own?
This is a straight loyalty and dedication question. Do not worry about the deep ethical and
philosophical implications. Just say yes.

38. Describe your management style.
Try to avoid labels. Some of the more common labels, like progressive, salesman or
consensus, can have several meanings or descriptions depending on which management
expert you listen to. The situational style is safe, because it says you will manage according
to the situation, instead of one size fits all.

39. What have you learned from mistakes on the job?
Here you have to come up with something or you strain credibility. Make it small, well
intentioned mistake with a positive lesson learned. An example would be working too far
ahead of colleagues on a project and thus throwing coordination off.

40. Do you have any blind spots?
Trick question. If you know about blind spots, they are no longer blind spots. Do not reveal
any personal areas of concern here. Let them do their own discovery on your bad points. Do
not hand it to them.

41. If you were hiring a person for this job, what would you look for?
Be careful to mention traits that are needed and that you have.

42. Do you think you are overqualified for this position?
Regardless of your qualifications, state that you are very well qualified for the position.

43. How do you propose to compensate for your lack of experience?
First, if you have experience that the interviewer does not know about, bring that up: Then,
point out (if true) that you are a hard working quick learner.

44. What qualities do you look for in a boss?
Be generic and positive. Safe qualities are knowledgeable, a sense of humor, fair, loyal to
subordinates and holder of high standards. All bosses think they have these traits.

45. Tell me about a time when you helped resolve a dispute between others.
Pick a specific incident. Concentrate on your problem solving technique and not the dispute
you settled.

46. What position do you prefer on a team working on a project?
Be honest. If you are comfortable in different roles, point that out.

47. Describe your work ethic.
Emphasize benefits to the organization. Things like, determination to get the job done and
work hard but enjoy your work are good.

48. What has been your biggest professional disappointment?
Be sure that you refer to something that was beyond your control. Show acceptance and no
negative feelings.

49. Tell me about the most fun you have had on the job.
Talk about having fun by accomplishing something for the organization.

50. Do you have any questions for me?
Always have some questions prepared. Questions prepared where you will be an asset to
the organization are good. How soon will I be able to be productive? and What type of
projects will I be able to assist on? are examples.

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Logic Gates

Logic Gates
NOT	AND	OR	NAND	NOR	XOR	XNOR

Introduction to Digital Logic Gates

A Digital Logic Gate is an electronic device that makes logical decisions based on the different combinations of digital signals present on its inputs. Digital logic gates may have more than one input but generally only have one digital output. Individual logic gates can be connected together to form combinational or sequential circuits, or larger logic gate functions.

Standard commercially available digital logic gates are available in two basic families or forms, TTLwhich stands for Transistor-Transistor Logic such as the 7400 series, and CMOS which stands for Complementary Metal-Oxide-Silicon which is the 4000 series of chips. This notation of TTL or CMOS refers to the logic technology used to manufacture the integrated circuit, (IC) or a “chip” as it is more commonly called.

Generally speaking, TTL logic IC’s use NPN and PNP type Bipolar Junction Transistors while CMOS logic IC’s use complementary MOSFET or JFET type Field Effect Transistors for both their input and output circuitry.

As well as TTL and CMOS technology, simple Digital Logic Gates can also be made by connecting together diodes, transistors and resistors to produce RTL, Resistor-Transistor logic gates, DTL, Diode-Transistor logic gates or ECL, Emitter-Coupled logic gates but these are less common now compared to the popular CMOS family.

Integrated Circuits or IC’s as they are more commonly called, can be grouped together into families according to the number of transistors or “gates” that they contain. For example, a simple AND gate my contain only a few individual transistors, were as a more complex microprocessor may contain many thousands of individual transistor gates. Integrated circuits are categorised according to the number of logic gates or the complexity of the circuits within a single chip with the general classification for the number of individual gates given as:

Classification of Integrated Circuits

• Small Scale Integration or (SSI) – Contain up to 10 transistors or a few gates within a single package such as AND, OR, NOT gates.
• Medium Scale Integration or (MSI) – between 10 and 100 transistors or tens of gates within a single package and perform digital operations such as adders, decoders, counters, flip-flops and multiplexers.
• Large Scale Integration or (LSI) – between 100 and 1,000 transistors or hundreds of gates and perform specific digital operations such as I/O chips, memory, arithmetic and logic units.
• Very-Large Scale Integration or (VLSI) – between 1,000 and 10,000 transistors or thousands of gates and perform computational operations such as processors, large memory arrays and programmable logic devices.
• Super-Large Scale Integration or (SLSI) – between 10,000 and 100,000 transistors within a single package and perform computational operations such as microprocessor chips, micro-controllers, basic PICs and calculators.
• Ultra-Large Scale Integration or (ULSI) – more than 1 million transistors – the big boys that are used in computers CPUs, GPUs, video processors, micro-controllers, FPGAs and complex PICs.

While the “ultra large scale” ULSI classification is less well used, another level of integration which represents the complexity of the Integrated Circuit is known as the System-on-Chip or (SOC) for short. Here the individual components such as the microprocessor, memory, peripherals, I/O logic etc, are all produced on a single piece of silicon and which represents a whole electronic system within one single chip, literally putting the word “integrated” into integrated circuit.

These complete integrated chips which can contain up to 100 million individual silicon-CMOS transistor gates within one single package are generally used in mobile phones, digital cameras, micro-controllers, PIC’s and robotic type applications.

Moore’s Law

In 1965, Gordon Moore co-founder of the Intel corporation predicted that “The number of transistors and resistors on a single chip will double every 18 months” regarding the development of semiconductor gate technology. When Gordon Moore made his famous comment way back in 1965 there were approximately only 60 individual transistor gates on a single silicon chip or die.

The worlds first microprocessor in 1971 was the Intel 4004 that had a 4-bit data bus and contained about 2,300 transistors on a single chip, operating at about 600kHz. Today, the Intel Corporation have placed a staggering 1.2 Billion individual transistor gates onto its new Quad-core i7-2700K Sandy Bridge 64-bit microprocessor chip operating at nearly 4GHz, and the on-chip transistor count is still rising, as newer faster microprocessors and micro-controllers are developed.

Digital Logic States

The Digital Logic Gate is the basic building block from which all digital electronic circuits and microprocessor based systems are constructed from. Basic digital logic gates perform logical operations of AND, OR and NOT on binary numbers.

In digital logic design only two voltage levels or states are allowed and these states are generally referred to as Logic “1” and Logic “0”, High and Low, or True and False. These two states are represented in Boolean Algebra and standard truth tables by the binary digits of “1” and “0”respectively.

A good example of a digital state is a simple light switch as it is either “ON” or “OFF” but not both at the same time. Then we can summarise the relationship between these various digital states as being:

Boolean Algebra	Boolean Logic	Voltage State
Logic “1”	True (T)	High (H)
Logic “0”	False (F)	Low (L)

Most digital logic gates and digital logic systems use “Positive logic”, in which a logic level “0” or “LOW” is represented by a zero voltage, 0v or ground and a logic level “1” or “HIGH” is represented by a higher voltage such as +5 volts, with the switching from one voltage level to the other, from either a logic level “0” to a “1” or a “1” to a “0” being made as quickly as possible to prevent any faulty operation of the logic circuit.

There also exists a complementary “Negative Logic” system in which the values and the rules of a logic “0” and a logic “1” are reversed but in this tutorial section about digital logic gates we shall only refer to the positive logic convention as it is the most commonly used.

In standard TTL (transistor-transistor logic) IC’s there is a pre-defined voltage range for the input and output voltage levels which define exactly what is a logic “1” level and what is a logic “0” level and these are shown below.

TTL Input & Output Voltage Levels

There are a large variety of logic gate types in both the bipolar 7400 and the CMOS 4000 families of digital logic gates such as 74Lxx, 74LSxx, 74ALSxx, 74HCxx, 74HCTxx, 74ACTxx etc, with each one having its own distinct advantages and disadvantages compared to the other. The exact switching voltage required to produce either a logic “0” or a logic “1” depends upon the specific logic group or family.

However, when using a standard +5 volt supply any TTL voltage input between 2.0v and 5v is considered to be a logic “1” or “HIGH” while any voltage input below 0.8v is recognised as a logic “0” or “LOW”. The voltage region in between these two voltage levels either as an input or as an output is called the Indeterminate Region and operating within this region may cause the logic gate to produce a false output.

The CMOS 4000 logic family uses different levels of voltages compared to the TTL types as they are designed using field effect transistors, or FET’s. In CMOS technology a logic “1” level operates between 3.0 and 18 volts and a logic “0” level is below 1.5 volts.

Then from the above observations, we can define the ideal Digital Logic Gate as one that has a “LOW” level logic “0” of 0 volts (ground) and a “HIGH” level logic “1” of +5 volts and this can be demonstrated as:

Ideal Digital Logic Gate Voltage Levels

Where the opening or closing of the switch produces either a logic level “1” or a logic level “0” with the resistor R being known as a “pull-up” resistor.

Digital Logic Noise

However, between these defined HIGH and LOW values lies what is generally called a “no-man’s land” (the blue area’s above) and if we apply a signal voltage of a value within this no-man’s land area we do not know whether the logic gate will respond to it as a level “0” or as a level “1”, and the output will become unpredictable.

Noise is the name given to a random and unwanted voltage that is induced into electronic circuits by external interference, such as from nearby switches, power supply fluctuations or from wires and other conductors that pick-up stray electromagnetic radiation. Then in order for a logic gate not to be influence by noise in must have a certain amount of noise margin or noise immunity.

Digital Logic Gate Noise Immunity

In the example above, the noise signal is superimposed onto the Vcc supply voltage and as long as it stays above the minimum level (Von-min) the input an corresponding output of the logic gate are unaffected. But when the noise level becomes large enough and a noise spike causes the HIGH voltage level to drop below this minimum level, the logic gate may interpret this spike as a LOW level input and switch the output accordingly producing a false output switching. Then in order for the logic gate not to be affected by noise it must be able to tolerate a certain amount of unwanted noise on its input without changing the state of its output.

Simple Basic Digital Logic Gates

Simple digital logic gates can be made by combining transistors, diodes and resistors with a simple example of a Diode-Resistor Logic (DRL) AND gate and a Diode-Transistor Logic (DTL) NAND gate given below.

Diode-Resistor Circuit	Diode-Transistor circuit
2-input AND Gate	2-input NAND Gate

The simple 2-input Diode-Resistor AND gate can be converted into a NAND gate by the addition of a single transistor inverting (NOT) stage. Using discrete components such as diodes, resistors and transistors to make digital logic gate circuits are not used in practical commercially available logic IC’s as these circuits suffer from propagation delay or gate delay and also power loss due to the pull-up resistors.

Another disadvantage of diode-resistor logic is that there is no “Fan-out” facility which is the ability of a single output to drive many inputs of the next stages. Also this type of design does not turn fully “OFF” as a Logic “0” produces an output voltage of 0.6v (diode voltage drop), so the following TTL and CMOS circuit designs are used instead.

Basic TTL Logic Gates

The simple Diode-Resistor AND gate above uses separate diodes for its inputs, one for each input. As a transistor is made up off two diode circuits connected together representing an NPN or a PNP device, the input diodes of the DTL circuit can be replaced by one single NPN transistor with multiple emitter inputs as shown.

As the NAND gate contains a single stage inverting NPN transistor circuit (TR₂) an output logic level “1” at Q is only present when both the emitters of TR₁ are connected to logic level “0” or ground allowing base current to pass through the PN junctions of the emitter and not the collector. The multiple emitters of TR₁ are connected as inputs thus producing a NAND gate function.

In standard TTL logic gates, the transistors operate either completely in the “cut off” region, or else completely in the saturated region, Transistor as a Switch type operation.

Emitter-Coupled Digital Logic Gate

Emitter Coupled Logic or ECL is another type of digital logic gate that uses bipolar transistor logic where the transistors are not operated in the saturation region, as they are with the standard TTL digital logic gate. Instead the input and output circuits are push-pull connected transistors with the supply voltage negative with respect to ground.

This has the effect of increasing the speed of operation of the emitter coupled logic gates up to the Gigahertz range compared with the standard TTL types, but noise has a greater effect in ECL logic, because the unsaturated transistors operate within their active region and amplify as well as switch signals.

The “74” Sub-families of Integrated Circuits

With improvements in the circuit design to take account of propagation delays, current consumption, fan-in and fan-out requirements etc, this type of TTL bipolar transistor technology forms the basis of the prefixed “74” family of digital logic IC’s, such as the “7400” Quad 2-input AND gate, or the “7402” Quad 2-input OR gate, etc.

Sub-families of the 74xx series IC’s are available relating to the different technologies used to fabricate the gates and they are denoted by the letters in between the 74 designation and the device number. There are a number of TTL sub-families available that provide a wide range of switching speeds and power consumption such as the 74L00 or 74ALS00 AND gate, were the “L” stands for “Low-power TTL” and the “ALS” stands for “Advanced Low-power Schottky TTL” and these are listed below.

• 74xx or 74Nxx: Standard TTL – These devices are the original TTL family of logic gates introduced in the early 70’s. They have a propagation delay of about 10ns and a power consumption of about 10mW.
• 74Lxx: Low Power TTL – Power consumption was improved over standard types by increasing the number of internal resistances but at the cost of a reduction in switching speed.
• 74Hxx: High Speed TTL – Switching speed was improved by reducing the number of internal resistances. This also increased the power consumption.
• 74Sxx: Schottky TTL – Schottky technology is used to improve input impedance, switching speed and power consumption (2mW) compared to the 74Lxx and 74Hxx types.
• 74LSxx: Low Power Schottky TTL – Same as 74Sxx types but with increased internal resistances to improve power consumption.
• 74ASxx: Advanced Schottky TTL – Improved design over 74Sxx Schottky types optimised to increase switching speed at the expense of power consumption of about 22mW.
• 74ALSxx: Advanced Low Power Schottky TTL – Lower power consumption of about 1mW and higher switching speed of about 4nS compared to 74LSxx types.
• 74HCxx: High Speed CMOS – CMOS technology and transistors to reduce power consumption of less than 1uA with CMOS compatible inputs.
• 74HCTxx: High Speed CMOS – CMOS technology and transistors to reduce power consumption of less than 1uA but has increased propagation delay of about 16nS due to the TTL compatible inputs.

Basic CMOS Digital Logic Gate

One of the main disadvantages with the TTL digital logic gate series is that the logic gates are based on bipolar transistor logic technology and as transistors are current operated devices, they consume large amounts of power from a fixed +5 volt power supply.

Also, TTL bipolar transistor gates have a limited operating speed when switching from an “OFF” state to an “ON” state and vice-versa called the “gate” or “propagation delay”. To overcome these limitations complementary MOS called “CMOS” logic gates using “Field Effect Transistors” or FET’s were developed.

As these gates use both P-channel and N-channel MOSFET’s as their input device, at quiescent conditions with no switching, the power consumption of CMOS gates is almost zero, (1 to 2uA) making them ideal for use in low-power battery circuits and with switching speeds upwards of 100MHz for use in high frequency timing and computer circuits.

This CMOS gate example contains 3 N-channel MOSFET’s, one for each input FET₁ and FET₂ and one for the output FET₃. When both the inputs A and B are at logic level “0”, FET₁ and FET₂ are both switched “OFF” giving an output logic “1” from the source of FET₃.

When one or both of the inputs are at logic level “1” current flows through the corresponding FET giving an output state atQ equivalent to logic “0”, thus producing a NAND gate function.

Improvements in the circuit design with regards to switching speed, low power consumption and improved propagation delays has resulted in the standard CMOS 4000 “CD” family of logic IC’s being developed that complement the TTL range.

As with the standard TTL digital logic gates, all the major digital logic gates and devices are available in the CMOS package such as the CD4011, a Quad 2-input NAND gate, or the CD4001, a Quad 2-input NOR gate along with all their sub-families.

Like TTL logic, complementary MOS (CMOS) circuits take advantage of the fact that both N-channel and P-channel devices can be fabricated together on the same substrate material to form various logic functions.

One of the main disadvantage with the CMOS range of IC’s compared to their equivalent TTL types is that they are easily damaged by static electricity so extra care must be taken when handling these devices. Also unlike TTL logic gates that operate on single +5V voltages for both their input and output levels, CMOS digital logic gates operate on a single supply voltage of between +3 and +18 volts.

In the next tutorial about Digital Logic Gates, we will look at the digital Logic AND Gate function as used in both TTL and CMOS logic circuits as well as its Boolean Algebra definition and truth tables.

XNOR Gates

XNOR gates have two bits of input and a single bit of output.

The output of XNOR gate is the negation of XOR and has logic '1' when both inputs are the same.

If you look carefully at the drawing of the gate, there is a second arc behind the first one near the inputs. Since this second arc is hard to see, it's usually a good idea to write the word "XNOR" inside the gate.

The truth table defines the behavior of this gate.

The function implmented by XNOR gates has interesting properties:

The function is symmetric. Thus, x XNOR y == y XNOR x. This can be verified by using truth tables.

The function is associative. Thus, (x XNOR y) XNOR z == x XNOR (y XNOR z). This can be verified by using truth tables.

Because of these properties, it's easy to define XNORn, which is an n-input XNOR gate.

XNORn(x1, x2,...,xn) = x1 XNOR x2 XNOR ... XNOR xn

That is, an XNOR gate with n-inputs is the XNOR of all the bits. This is not ambiguous because the XNOR function is associative (all parenthesization of this expression are equivalent).

(Error-checkers! You may wish to verify this, and email me if this is incorrect!).

XOR Gates

XOR gates have two bits of input and a single bit of output. The output of XOR gate is logic '1' only if the inputs have opposite values. That is, when one input has value logic '0', and the other has value logic '1'. Otherwise, the output is logic '0'.

This is called Exclusive-OR. The definition of OR is inclusive-or, where the output is logic '1' if either input is logic '1', or if both inputs are logic '1'.

XOR can be defined using AND, OR, and NOT.

x XOR y == ( x AND (NOT y) ) OR ( (NOT x) AND y ) 

Here's a diagram of the XOR2 gate.

If you look carefully at the drawing of the gate, there is a second arc behind the first one near the inputs. Since this second arc is hard to see, it's usually a good idea to write the word "XOR" inside the gate.

The truth table defines the behavior of this gate.

The function implmented by XOR gates has interesting properties:

The function is symmetric. Thus, x (+) y == y (+) x. This can be verified by using truth tables. (We use (+) to denote logical XOR--ideally, we'd draw it with a + sign inside a circle, but HTML doesn't seem to have a symbol for this).

The function is associative. Thus, [ x (+) y ] (+) z == x (+) [ y (+) z ]. This can be verified by using truth tables.

Because of these properties, it's easy to define XORn, which is an n-input XOR gate.

XORn(x1, x2,...,xn) = x1 (+) x2 (+) ... (+) xn

That is, an XOR gate with n-inputs is the XOR of all the bits. This is not ambiguous because the XOR function is associative (all parenthesization of this expression are equivalent).

NOR Gates

NOR gates have two bits of input and a single bit of output. The output of NOR gate is the negation of OR gate.

The truth table defines the behavior of this gate.

The function implmented by NOR gates has interesting properties:

The function is symmetric. Thus, x NOR y == y NOR x. This can be verified by using truth tables.
The function is not associative. This can be verified by using truth tables.
Because of these properties, NORk is defined from ORk and NOT built from NOR gates.