The Linux kernel has its own virtual address space, as every user mode process does. The virtual address space of the kernel (1 GB sized in a 3G/1G split) is divided into two parts:
- Low memory or LOWMEM, which is the first 896 MB
- High memory or HIGHMEM, represented by the top 128 MB
Physical mem
Process address space +------> +------------+
| | 3200 M |
| | |
4 GB +---------------+ <-----+ | HIGH MEM |
| 128 MB | | |
+---------------+ <---------+ | |
+---------------+ <------+ | | |
| 896 MB | | +--> +------------+
3 GB +---------------+ <--+ +-----> +------------+
| | | | 896 MB | LOW MEM
| ///// | +---------> +------------+
| |
0 GB +---------------+
