Bounds checking, explicit unsafe blocks, proper strings, explicit type conversions, proper enumerations, checked arithmetic.

For example, ESPOL/NEWP was the first systems programming language with explicit unsafe blocks, 8 years before C came into the world.

So hardware that was much weaker than PDP-11, and yet capable of supporting such security features.

Burroughs B5000 OS is still being developed, nowadays known as Unisys ClearPath MCP, and its top selling feature is being a mainframe system for customers whose security is the top priority.

> Burroughs B5000 OS is still being developed, nowadays known as Unisys ClearPath MCP, and its top selling feature is being a mainframe system for customers whose security is the top priority.

What's special about it?

Implemented in a systems programming language has everything security related that C lacks.

> Bounds checking, explicit unsafe blocks, proper strings, explicit type conversions, proper enumerations, checked arithmetic.

Plus a capabilities based security access, and unsafe blocks taint binaries, requiring admin permission to be executed.

Are these OS or hardware features?

Language and OS features.

Recent hardware versions use Xeons.

Again, just features missing from C, and available in other languages.

Another notable feature, it did not make use of any Assembly, in 1961, because all CPU features are exposed as compiler intrinsics.