Hi, I just started reading Memory Managment chapter from book Professional Linux Kernel Architecture. At very start of chapter I came across terms FLATMEM, DISCONTIGMEM and SPARSEMEM. Out of these DISCONTIGMEM and SPARSEMEM are available to NUMA systens only. Book also says UMA systems can also choose DISCONTIGMEM option if there address space contains large holes. Some googling says DISCONTIGMEM is prefered when we have physical discontiguous memory. This is what I don't understand what does it mean by containing large holes? physical discontiguous memory? Is it like when I put 2 RAM chips in a system then memory for them will be discontiguous? Would /proc/iomem give me details I wanted? Per my understanding RAM memory will ALWAYS be contiguous whether its 512 MB or 4 GB. Please give me graceful example of discontiguous physical memory That will really help me out.