<p>Earlier blocks had fewer transactions, and so were smaller. Later blocks have many transactions, and so are much larger.</p>

CC BY-SA 3.0
2013-04-07T13:10:11.513Z
But, I thought I only need to verify one hash per block(?)

What would I need to verify per transaction? Are you saying I need to verify one hash per transaction? 

Also, I understood that each block has its size capped at few Mb.
Sida Zhou
CC BY-SA 3.0
2013-04-07T16:21:25.273Z
@SidaZhou There are two major bottlenecks in synchronization. One is signature verification, and the other is looking up the inputs on disk and marking them spent. Both increase when transactions increase.
Nick ODell
CC BY-SA 3.0
2013-04-07T12:53:39.130Z
2013-04-07T12:53:39.130Z
user4028
<p>The hash verifies that it's part of the chain but it doesn't verify that it's legal.  For example, it might contain fake transactions that invent money and send it to people.</p>

<p>Well-behaved software needs to check this, too.  I think that the download time is what dominates the slowness, not checking the transactions.</p>

CC BY-SA 3.0
2013-04-07T17:43:59.910Z
2013-04-07T17:43:59.910Z
Eyal
<p>I'm truly lost about how bitcoin works.</p>

<p>I understand a blockchain contains all transactions ever made. So, what things need to be verified while I'm downloading the whole blockchain? If it's just the hash of each block, the processing/verification speed of earlier blocks should be same as later blocks, right? </p>

<p>Only better guess I have, is that if anything need to be indexed, then that would explain why later blocks are slower. So is this the case?</p>

<blockchain>
Why verifying later blockchain is slower?
Sida Zhou
# Why verifying later blockchain is slower?

(Asked by: username_0 on 2013-04-07)

I'm truly lost about how bitcoin works.

I understand a blockchain contains all transactions ever made. So, what things need to be verified while I'm downloading the whole blockchain? If it's just the hash of each block, the processing/verification speed of earlier blocks should be same as later blocks, right?

Only better guess I have, is that if anything need to be indexed, then that would explain why later blocks are slower. So is this the case?

**Tags:** blockchain


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## 2 answers

### Answer by username_1 on 2013-04-07. Score: 4

Earlier blocks had fewer transactions, and so were smaller. Later blocks have many transactions, and so are much larger.

> **Comments:**
> **username_0**: But, I thought I only need to verify one hash per block(?)  What would I need to verify per transaction? Are you saying I need to verify one hash per transaction?   Also, I understood that each block has its size capped at few Mb.  
> **username_2**: @SidaZhou There are two major bottlenecks in synchronization. One is signature verification, and the other is looking up the inputs on disk and marking them spent. Both increase when transactions increase.  

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### Answer by username_3 on 2013-04-07. Score: 0

The hash verifies that it's part of the chain but it doesn't verify that it's legal. For example, it might contain fake transactions that invent money and send it to people.

Well-behaved software needs to check this, too. I think that the download time is what dominates the slowness, not checking the transactions.


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