In the previous three articles in this series, I have looked individually at:
In this, the fourth and definitely last of what should have been a series of three articles, I’m going to try to summarise those in a single diagram. This shows a single disk which has three partitions: the mandatory hidden EFI partition, one for an HFS+ volume, and one for an APFS container, within which there is a single APFS volume.
This is also available as a downloadable PDF for you to refer to: DiskStructure1015over
Further references which provide fuller details are:
Wikipedia on GPT disk structure
Wikipedia on HFS+
Apple’s TN1150 HFS Plus Volume Format
Apple File System Reference (PDF)
Wikipedia on B-Trees, which are used extensively in both file systems
Boot volume layout (macOS 10.15 and 11.0).