23 May 2023

What is Segwit? Bitcoin's Scalability Upgrade Explained

Delve into the intricacies of SegWit, the groundbreaking protocol upgrade that revolutionized Bitcoin's scalability. Discover its technical details, history, and impact on the cryptocurrency ecosystem.

What is Segwit? Bitcoin's Scalability Upgrade Explained


    What is SegWit, and...
    Segwit History and The...
    How Does SegWit Work?
    Advantages of SegWit
    Potential Drawbacks and Counterarguments
    Impact on the Bitcoin...

As the world of cryptocurrencies matures, the technical landscape becomes increasingly sophisticated. One of the most significant advancements in the Bitcoin network is the implementation of Segregated Witness, or SegWit. This comprehensive guide explains the technical details of SegWit, its impact on the Bitcoin network, and its implications for other cryptocurrencies. So get ready to dive deep into the inner workings of this revolutionary protocol upgrade.

What is SegWit, and Why Was It Introduced?

SegWit was a protocol upgrade implemented in the Bitcoin network in 2017. Its primary purpose was to address the scalability issues that emerged as Bitcoin's user base and transaction volume grew exponentially. These issues led to longer transaction times and higher fees and hindered the development of advanced features like the Lightning Network.

The primary goal of SegWit was to optimize the way transaction data is stored within Bitcoin blocks, thereby allowing more transactions to be processed in each block without increasing the block size itself. This optimization not only sought to increase the transaction capacity of the Bitcoin network but also mitigate transaction malleability, an issue that can hinder the development of advanced features like the Lightning Network.

Segwit History and The Block Size Wars

As discussed, the history of SegWit and The Block Size Wars be traced back to the early days of Bitcoin when the network began to experience growing pains due to the rapid increase in transaction volume. As a result, the limited block size of 1MB, initially intended as a temporary measure to prevent spam transactions, became a point of contention among developers and the wider Bitcoin community.

Throughout the years, various proposals were put forth to address the block size issue, such as Bitcoin XT, Bitcoin Classic, and Bitcoin Unlimited, which sought to increase the block size limit. However, these proposals needed to gain more consensus to be implemented. In 2015, Bitcoin developer Pieter Wuille introduced the concept of Segregated Witness, or SegWit, which aimed to increase transaction capacity without directly increasing the block size. SegWit sparked extensive debates within the Bitcoin community, with some embracing the innovative solution, while others continued to push for a block size increase.

Two primary factions emerged:

  1. Those advocating for a block size increase (big-blockers)
  2. Those in favor of finding alternative solutions to improve scalability without increasing the block size (small-blockers).

The big-blockers argued that a simple increase in block size would accommodate the rising transaction volume and reduce fees. In contrast, the small-blockers were concerned that larger blocks could lead to greater centralization, as increased storage and processing requirements could push smaller miners and nodes out of the ecosystem.

The block size wars peaked in 2017 with the activation of SegWit on the Bitcoin network and the subsequent creation of Bitcoin Cash, a hard fork of Bitcoin that increased the block size to 8MB. The split highlighted the deep divisions within the community regarding the best approach to scaling the network. Since then, SegWit has been adopted by an increasing number of wallets and service providers, and its benefits, such as lower transaction fees and improved confirmation times, have become more pronounced. Meanwhile, the block size debate has continued, albeit less intensely, as the focus has shifted toward developing second-layer solutions like the Lightning Network and other potential protocol upgrades that could further improve Bitcoin's scalability and efficiency.

How Does SegWit Work?

To understand SegWit's inner workings, knowing how Bitcoin transactions are structured is essential. Traditional Bitcoin transactions consist of two main parts: inputs and outputs. Inputs refer to the source of the bitcoins (the sender's address), while outputs designate the recipient's address. In a standard transaction, the input contains the signature, or "witness" data, which is used to verify that the sender has the necessary funds and the right to spend them.

In the original Bitcoin protocol, the witness data was included within the transaction itself. The size of the witness data varies, but it can be quite large, taking up a substantial portion of the transaction size. As a result, the limited block size of 1MB imposed a constraint on the number of transactions that could be included in a block.

SegWit, as the name suggests, segregates the witness data from the main transaction data. Instead of being included directly within the transaction, the witness data is stored separately in an extended block, called a "witness block." This separation enables more transactions to fit within a block without increasing the block size. In technical terms, SegWit introduces a new concept called "block weight," which combines the original block size and the segregated Witness data. The maximum block weight is set to 4 million weight units, with a 1MB block size limit still in place.

Advantages of SegWit

  1. Improved Scalability: By segregating witness data, SegWit effectively increases the block weight without requiring a hard fork, allowing the network to process more transactions.
  2. Faster Transaction Times: As more transactions can be included in a block, the average confirmation time for transactions is reduced, leading to faster transaction processing.
  3. Reduced Transaction Fees: With more space in each block, competition for block inclusion is less intense, leading to lower transaction fees.
  4. Enhanced Security: SegWit mitigates transaction malleability, a vulnerability that could be exploited to manipulate transaction IDs. This improvement enhances the network's security and enables the development of second-layer solutions like the Lightning Network.
  5. Future Compatibility: SegWit paves the way for future protocol upgrades, such as Schnorr signatures and Taproot, which aim to improve transaction privacy and efficiency further.

Potential Drawbacks and Counterarguments

Critics of SegWit argue that it is a temporary solution to Bitcoin's scalability problem and that a block size increase will eventually be necessary. However, proponents of SegWit contend that with continued optimization and the development of second-layer solutions, the need for a block size increase can be delayed or even avoided entirely. Furthermore, increasing the block size could lead to centralization issues, as larger blocks require more storage and processing power, potentially pricing out smaller miners and nodes.

Another criticism is that SegWit adoption by wallets and service providers was initially slow, leading to a lower-than-expected impact on transaction capacity. However, SegWit adoption has since increased, and as more industry players support it, the network benefits continue to grow. Additionally, the development of new wallet software and improvements in user interfaces have made it easier for users to take advantage of SegWit's features.

Impact on the Bitcoin Network and Other Cryptocurrencies

Since its introduction, SegWit has positively impacted the Bitcoin network. Transaction fees have decreased, confirmation times have improved, and the network's overall capacity has increased. Additionally, SegWit has paved the way for developing the Lightning Network, a second-layer solution that enables instant, low-cost Bitcoin transactions. The Lightning Network operates on the Bitcoin blockchain, leveraging SegWit's malleability fix to facilitate secure off-chain transactions.

SegWit has also been adopted by other cryptocurrencies, such as Litecoin and Vertcoin, showcasing its versatility and effectiveness as a scaling solution. The adoption of SegWit by these cryptocurrencies has led to similar improvements in transaction capacity, fees, and confirmation times.


Segregated Witness is a key development in cryptocurrencies, providing a balanced and technically sound solution to Bitcoin's scalability problem. By understanding the technical details and advantages of SegWit, it becomes clear that this protocol upgrade has been instrumental in driving the Bitcoin network's ongoing evolution. As SegWit continues to be adopted and integrated into new technologies and cryptocurrencies, its impact on the entire blockchain ecosystem will likely grow, further solidifying its place as a cornerstone of the digital currency revolution.
Please be aware that: Cryptocurrencies are unregulated in the UK; Cryptocurrencies are not protected under Financial Ombudsman Service or Financial Services Compensation Scheme (FSCS); Profits may be subject to capital gains tax; The value of investments can go down as well as up.

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