EBS talks about IOPS. However, what does IOPs actually mean?
I have found this online:
"IOPS (input/output operations per second) is a popular performance metric used to distinguish one storage type from another."
Ok, but what type of input/output operation are we talking about? Let's say I want to read a 1GB file vs 1MB I can't imagine that both would be just a single IOP. Thus far IOPs in my mind is a unit that is not tied to a physical measure. Hence the question of what actually is an IOP?
As @jordanm already mentioned in a comment to your question, each read operation can only read up to the block size. And the block size of GUID partition table (GPT), which is a common partitioning scheme, is 4096 bytes.
You can calculate throughput in MB/s by multiplying IOPS with block size. So given an IOPS of 3000 and a default block size of 4096 bytes (4KB) you would have:
3,000 * 4KB = 12,000 KB/s = ca. 12 MB/s