The name KPRCB stands for (Kernel) Processor Control Block. The kernel keeps one for each logical processor as the last member of the processor’s KPCR. The KPRCB (formally a _KPRCB) holds most of what the kernel needs ready access to while managing a processor and while managing resources that are themselves managed more simply and quickly per processor.

The KRCB is highly specific to the processor architecture. Indeed, public symbol files confirm that Microsoft differentiates the x86 and x64 implementations not by conditional compilation but by defining them in separate headers (i386_x.h and amd64_x.h). This website’s attempt at documentation follows what’s known of Microsoft’s source code and presents the x86 KPRCB and x64 KPRCB separately.