The original Hiren’s BootCD (up to version 15.2, released in 2012) relied on a mixture of DOS-based utilities and a very stripped-down "Mini Windows XP" environment. It was built primarily around 32-bit compatibility.
: The 32-bit execution layer natively addresses up to 4 GB of RAM. This makes it highly lightweight, capable of running smoothly on older machines with as little as 1 GB to 2 GB of physical system memory. Core Diagnostic and Repair Categories Within HBCD Hbcd-pe-x32.iso