This is a improved version of xv6 which is originally written by MIT teachers.
What I've done:
1. Add some system calls like find, xargs, sysinfo.
2. Improve the pagetable of xv6. Each process of original xv6 has only one user pagetable and there is only one kernel pagetable for all the process. I add a kernel page table for each of the process which can speed the conversion of user virtual address to physical address in supervise mode.
3. Add lazy allocation and copy on write fork which will improve the response efficiceny of xv6.
4. Add user thread which can switch thread in user mode.
5. Make the xv6 support large files which is up to 64 MB.