1. Throughput Optimized HDD (st1)
Designed for frequent, large, sequential workloads like big data, data warehouses, and log processing.

Lower cost than SSDs.

Offers high throughput but lower IOPS.

2. Cold HDD (sc1)
Ideal for infrequent access and cold data like backups or older data.

Lowest-cost EBS storage option.

Lower performance compared to st1, suitable for less demanding workloads.

Both types are magnetic storage and are used for cost-effective large data volumes where speed is not a top priority.