setjmp/longjmp try/catch
    

kernel vs root
    kernel mode = HW protection = instructions may run, pages may be accessed
    root account = OS protection = system call behavior
privilege escalation
    get something with more priviledge to make a mistake in your favor

half-duplex vs bus
    du = 2 duplex = 2 parties talking
    bus = multi-party half-duplex
    both:
        listening == not speaking
        speaking
            1
            0
        only 1 speaker at a time
bridges
    connection between two busses
DMA = direct memory access
    non-CPU reads or writes to RAM without telling the CPU
    physical address

trap vs fault
    fault = something goes wrong
        page fault -- fault caused by a missing PTE
    trap = meant to be exceptional
exception categories (both methods)
    Cause                                   Result
    ----------                              ---------------
    trap                                    trap -- got to next
    fault                                   fault -- re-run
    interrupt                               interrupt -- go to next
                                            abort -- stops and never comes back


signals
    OS -> user code communication
    like a SW-only interrupt
    most of them abort unless you add a handler
    a few cannot be handled (SIGKILL, SIGSTOP, ...)

why do PTs save memory
    PT = use more memory than no page table
    2+ processes, PT allows both to have memory without collisions
    MLPT less mem tha SLPT
        because MLPT (tree), we can omit entire subtress

network levels (categories)
    -- out of scope
URLs
    -- host is imporant to us
DHCP vs DNS
    DHCP = "hey, I want an IP address?"
        1.  your computer: "I want IP"
        2.  router: "I've got 1.2.34.56; do you want it?"
        3.  your computer: "I want 1.2.34.56!"
        4.  router: "OK"
    DNS = "what's the IP address of www.example.com?"
go over ungraded quiz