A lot of disk benchmarking software has a benchmark that's called 4K Random Read Speeds. Basically it measures how fast the storage device can read random small bits of data. It's the one benchmarking number that most closely mirrors everyday computing such as when you're loading a program or booting your OS.
If you want to see some really pathetic numbers, go find out the 4K Random Read Speeds of a typical hard drive. You'll weep when you see the numbers. For instance, take a Western Digital Black Edition hard drive. It's often referred to as one of the fastest consumer hard drives on the market but their 4K Random Read Speeds are sub-1 MB/s compared to an SSD in which you'll find that 4K Random Read Speeds are in excess of 30 MB/s. And now you know why an SSD is faster than a spinning hard drive.