Disk I/O question

This is my device:
iMac
  • 3.1 GHz 6-core Intel Core i5

  • APPLE SSD SM0512L

iPhone X

I have a folder with many pictures (50kb~500kb/each), and it takes a long time to read a picture from this folder.
Code Block objc
NSURL *filePath = ...
NSData *data = [NSData dataWithContentsOfURL:filePath];

How many files are usually recommended to store in a folder?
Disk I/O question
 
 
Q