# <center><i class="fa fa-edit"></i> 3.6 Limitations and Improvements)</center>
###### tags: `Blockchain`
The following notes are taken from [Coursera](https://www.coursera.org/learn/cryptocurrency/home/week/2)

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### Hard-coded Limits
- 10 min average creation time per block
- 1M bytes in a block
- 20,000 signature operations per block
- 100M satoshis per bitcoin*
- 21M total bitcoins max*
- 50, 25, 12.5 ... bitcoin mining reward*

*affect economic balance of power; too much to change now

### Throughput Limits
- 1M bytes per block (10 min)
- > 250 bytes per transaction
- 7 transactions per second

**COMPARE TO**
- VISA: 2,000-10,000 transactions per second
- Paypal: 50-100 transactions per second

### Cryptographic Limits in Bitcoin
- Only 1 signature algorithm (ECDSA/P256)
- Hard-coded hash functions
- Crypto primitives *might* break by 2040

### "Hard-forking" Changes to Bitcoin
- Old nodes will never catch up because the system will keep rejecting until they update to the new software

**CURRENTLY UNLIKELY**
- New op codes
- Changes to size limits and mining rate
- Many small bug fixes

### Soft Forks -> Temp Fork (i.e. Pay-To-Script-Hash)
- Add new features which only *limit* the set of valid transactions
- Need majority of nodes to enforce new rules
- Old nodes will approve

**RISK**
Old nodes might be mining now-invalid blocks
- New signature schemes
- Extra per-block metadata
- Shove in coinbase parameter
- Commit to UTXO tree in each block