unchecked_isa_dma

Some host adapters use Direct Memory Access (DMA) to read and write blocks of data directly from or to the computer's main memory. <#1280#><#1280#> is a virtual memory operating system that can use more than 16~MB of physical memory. Unfortunately, on machines using the ISA bus, DMA is limited to the low 16~MB of physical memory. If the 31 bit is set, the high-level code will provide data buffers which are guaranteed to be in the low 16~MB of the physical address space. Drivers written for host adapters that do not use DMA should set this bit to zero. Drivers specific to EISA bus machines should also set this bit to zero, since EISA bus machines allow unrestricted DMA access.