Burroughs large systems descriptors

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Descriptors^{[1] [2]} are an architectural feature of Burroughs large systems, including the current (as of 2024) Unisys Clearpath/MCP systems. Apart from being stack- and tag-based, a notable architectural feature of these systems is that they are descriptor-based. Descriptors are the means of having data that does not reside on the stack such as arrays and objects. Descriptors are also used for string data as in compilers and commercial applications.

Descriptors are integral to the automatic memory management system and virtual memory. Descriptors contain metadata about memory blocks including address, length, machine type (word or byte — for strings) and other metadata. Descriptors provide essential memory protection, security, safety, catching all attempts at out-of-bounds access and buffer overflow. Descriptors are a form of capability system.^[3]