It is my pleasure to attend lecture for beginners course, task 4. I must say that the previous lectures have been awesome. Thanks to all professor who have taken their time to put the resources together to come up with detailed lessons.
As usual, task four also has 3 questions as homework and each student is expected to attempt any one out of the three. So, I will choose question 1. It reads

What is the difference between PoW & PoS? Advantages & Disadvantages? Which one is better in scaling Capacity? Examples?

I will be answering this question based on my understanding of the lecture and personal research.
To make this question easier for the readers, I have decided to separate this question into four parts as this:

1. Difference between PoW and PoS
2. Advantages and Disadvantages of PoW and PoS
3. Which one is better in scaling Capacity?
4. Examples of cryptocurrencies using PoW and PoS

Difference Between PoW and PoS

In order to understand the difference between PoW and PoS, we need to Know what they really are. It is pertinent to know that PoW and PoS are consensus mechanism. The word 'consensus' means a general agreement about something. And the word 'mechanism' is a way or process in which something is done.
According to Oxford Dictionary, Mechanism is:

a natural or established process by which something takes place or is brought about.

Therefore, consensus mechanism is a way or process in which agreement is being reached on blockchain. Consensus mechanism or protocol keeps the distributed networks together. It is the consensus mechanism that makes all nodes(nodes are devices connected to a network) to agree together and validate each transaction on the network.

That being said. Let's start with PoW

What is PoW?

PoW means Proof of Work. Proof of work is a type of consensus protocol or mechanisms which uses computational puzzles to validate transaction that's initiated on the network. Proof of work is widely known among other types of consensus mechanisms because it's first used by first cryptocurrency, Bitcoin.

What is PoS?

PoS means Proof os Stake. Proof of stake is another type of consensus mechanism in which validators are selected to validate the transactions. Validators are selected based on the number of coins they hold or stake.

Having established this fact, let's try to look at the difference between the two.

S/N	Proof of Work (PoW)	Proof os Stake (PoS)
1.	In proof of work, miners are required to validate the transactions by solving a mathematical puzzles.	Here, instead of miners, validators are selected based on stake. The persons who have higher stake are selected as validators.
2.	Proof of work requires a lot of computing power, hence it consumes lot of energy	Proof of stake doesn't consume energy since it doesn't require mathematical puzzles.
3.	In PoW, a miner must invest in hardware in order to effectively mint.	In PoS, a validator has to invest invest more on the coins to have higher stake
4.	The first miner that solves the puzzles is given the block reward	The validator receives the network fee in PoS.

_{Table: Difference Between Proof of Work (PoW) and Proof of Stake (PoS)}

2. Advantages and Disadvantages of PoW and PoS

Having differentiated between PoW and PoS, let's now look at the advantages and disadvantages of them

Advantages of Proof of Work (PoW)

1. In PoW, it's miners who validate the transactions and they don't have to have higher stake as it is in PoS.
2. Degree of decentralization is much more better in PoW and that's what makes it unique.
3. PoW as a consensus mechanism is very safe for blockchain because of it's ability to create more immutable blockchain.

Disadvantages of Proof of Work (PoW)

1. Because validity of transaction requires solving mathematical puzzles when a PoW consensus protocol is used for cryptocurrency, it is therefore leads to a lot of computing efforts for miners.
2. There's energy consumption in PoW because of lots of computing efforts.
3. Proof of work consensus protocol demands a lot of miners for maximum security. If the numbers of miners are not enough, the security of the blockchain is not guaranteed as there may be attacks from the hackers.
4. The first miner that finds answer receives block reward and the remaining ones aren't rewarded. Hence, it leads to wastes of resources for several hundred of miners.

Advantages of Proof of Stake (PoS)

1. Unlike PoW, PoS doesn't consume energy since it doesn't require a lot of computing power, hence it is energy efficient.
2. Another advantage of PoS is that stakeholders earn their rewards unlike PoW where not all miners are rewarded.
3. PoS doesn't not require mathematical computational before the validators can validate the transactions. Hence, it doesn't waste time and provides high speed.
4. The validators or stakers can sell their collateral anytime they wish to sell.

Disadvantages of Proof of Stake (PoS)

1. Proof of Stake requires that one invest on the coins in order to have higher stake. Hence it limits people who don't have enough resource to invest to participate as validators.
2. Since validators are selected based on the number of coins they own. Hence, the those who have enough coins or have higher stake are liable to be selected as validators. This seems to lead to centralized system.
3. Comparing PoS to PoW in security, PoS is less secure.

3. Which one is better in scaling Capacity?

In order to understand this, we need to know what scaling capacity is. Scaling Capacity in blockchain is the ability of the network to handle a large amount of transactions with in a very short period of time.
Proof os Stake (PoS) is better in scaling capacity than Proof of Work (PoW). The reason is, it can handle more transactions at once than PoW.

4. Examples of Cryptocurrencies Using PoW and PoS

Listed below are some of the examples of coins that use PoW and PoS.

Some of the Cryptos using PoS are:

✓Cardano
✓ Polkadot
✓ Bitshares
✓ EOSIO
✓ Gridcoin

Some of the Cryptos using PoW are:

✓ Bitcoin
✓ Dogecoin
✓ LITECOIN
✓ Namecoin
✓ Monero
✓ Titcoin
✓ Bitcoin Cash
✓ Zcash

These Cryptos below use both PoW and PoS

✓ Decred
✓ Peercoin

Conclusion

Consensus mechanism is needed on every blockchain so as to validate the transactions on the network. It is the consensus mechanism that serves as a backbone of blockchain. Without a secure protocol on blockchain, the blockchain is liable for attack.

There are many types of these consensus protocol used on blockchain. Two of them (PoW and PoS) are discussed in this homework article. Some of those that are used which are not discussed in this article are , Delegate Proof of Stake (DPoS), Proof of Burn (PoB), Practical Byzantine Fault Tolerant (pBFT) etc.