Solid-state drives (SSDs) are expensive, especially if want a capacity above 1TB. That's why hard drives still rule the roost, even though they don't offer the speed of an SSD. Apple's software-based Fusion Drive provides a compromise: it uses a small amount of high-performance SSD alongside a higher-capacity HDD. macOS caches frequently used drive-based data in the SSD, boosting performance.
When deciding on a drive for an iMac I purchased earlier this year, I felt that the performance I’d get from the $700 jump from a 1TB Fusion Drive to a 1TB SSD simply wasn’t worth it. Apple pairs a 32GB SSD with its 1TB hard drive, and 128GB with its 2TB and 3TB options.
