# A technical work through of How Solana Blockchain perform higher
Solana is a high perfomance blockchain achieving 710k transaction pr second usingProof of History(POH) combined with proof of stake consensus and Proof of Replication(POR)
## Proof of History( POH ):
This is a cryptographic clock that proofs time has passed between events without relying on timestamps or synchronised clock across nodes.
timestamp or synchronized clocks are used to determined which event occur first?, how much time passed between two events?.
Proof of History(POH) ask: "can we proof time passed without using clock at all?".
## Proof of History(POH) Hashing:
- It is an algorithm that create a time ordering to allow the validator nodes to determined the order of incoming block that the leader generates.
- 

- uses a sequential hash function SHA-256 which is a deterministic machine where each output becomes the next input createing a verifiable delay function hash(n+1) = SHA-256(hash(n)). Each hash is numbered with an index counter.
hash1 = SHA-256("starting value")
hash2 = SHA-256(hash1)
hash3 = SHA-256(hash2)
hash4 = SHA-256(hash3)
hashN = SHA-256(hashN-1)
so each hash depens on the previous hash i.e you mush wait for hash(n) before computing hash(n+1) which create a cryptographic stopwatch.
## how POH timestamped events like transactions without clock:
hash336 = SHA-256(hash335 + event_data)
this means events was inserted into the chain after hash335 before hash336 finish computing so that anyone can verify that the event has happened before hash336 existed.
*"No clock, No Timestamp, Just Math"*
this makes POH to sometimes called ***Cryptographic clocK*** 
## The How?
The Leader generates POH sequentially and
Validators verify POH + Signature in parallel using:
- GPU cores
- SIMD instructions(Single Instruction Multiple Data).
and this is highly effecient because Solana uses EdDSA/Ed25519 which is an Edward-Curve Digital Signature Algortithm built on a twisted Edward Curve Designed for:
- Speed
- Safety
- Simplicity
## Why Solana Chose Ed25519:
- Ed25519 support effecient batch verification which is critical for solana's parallel execution model.
- very high throughput.
- predictable performance.
- Ed25519 is deterministic and does not rely on randomness during signing.

## summary
Solana is design for cheap verification in parallel and generate evennts in sequential order(POH) which is what makes it keep latency very low.
it doest it by GPU verification which is many independent check at once.
secondly by SIMD which is One instruction applied to many values.
SIMD + GPU = Massive Parallelism.
practically thousand cores x Multiple values per instruction.
### Verification speed:
this is determined by:
**Generation time: Total Hashes/(hash-per-second-single-core)**
**Verification time: Total Hashes/(hash-per-second x number of cores)**

### Security:
- **Client Consistency:**
- Users include last observed hash in their transaction, preventing reordering attack.

### Timestamping Events
- insert data into sequence by hashing it with current state
*hash336 = SHA-256(Append(hash335, event_data))*
this proves that the event happened before hash-336 was generated.