Conceptual, architectural explainers — how a subsystem actually works underneath.
The clever reload-from-disk trick that let DOS's COMMAND.COM recover automatically after a large program overwrote its expendable transient portion.
FreeDOS's kernel is a from-scratch, clean-room reimplementation, and its authors' actual architecture choices differ deliberately from how MS-DOS was built.
How DOS users reclaimed conventional memory by relocating drivers and TSRs into unused upper memory gaps, which varied by machine and BIOS.
Why DOS ended up with three separate, incompatible ways to access memory beyond the conventional 640K barrier, and what each one was actually solving.
How to design a FreeBSD service around Capsicum descriptor rights, capability mode, process descriptors, and delegated Casper services.
How HAST replication modes, role changes, fencing, and CTL iSCSI targets fit together without confusing replication with failover.
How FreeBSD seeds Fortuna, harvests entropy, serves random bytes, and exposes early-boot failures without making unsafe assumptions.
How FreeBSD orders rc.d scripts, separates dependency order from enablement, and provides safe, testable service lifecycle hooks.
How FreeBSD routes path lookup and file operations through mounts, vnodes, namecache entries, and filesystem-specific VOP methods.
How Haiku BFS combines typed attributes, per-volume indexes, query predicates, live updates, B+trees, and journaling without becoming SQL.