host# cd /dev
host# ls
acpi consolectl lpt0.ctl stdout ttyva
ad4 ctty mdctl sysmouse ttyvb
ad4s1 cuaa0 mem ttyd0 ttyvc
ad4s1a cuaia0 net ttyid0 ttyvd
ad4s1b cuala0 net1 ttyld0 ttyve
ad4s1c devctl net2 ttyp0 ttyvf
ad4s1d devstat net3 ttyp1 urandom
ad4s1e fd network ttyv0 usb
ad4s1f fd0 nfs4 ttyv1 usb0
ad4s1g fido null ttyv2 usb1
ad6 geom.ctl pci ttyv3 usb2
ad6s1 io ppi0 ttyv4 usb3
ad6s1c kbd0 ptyp0 ttyv5 xpt0
apm klog ptyp1 ttyv6 zero
ata kmem random ttyv7
atkbd0 log stderr ttyv8
console lpt0 stdin ttyv9
sghost# mount
/dev/ad4s1a on / (ufs, local)
devfs on /dev (devfs, local)
/dev/ad4s1f on /home (ufs, local, soft-updates)
/dev/ad4s1g on /tmp (ufs, local, soft-updates)
/dev/ad4s1d on /usr (ufs, local, soft-updates)
/dev/ad4s1e on /var (ufs, local, soft-updates)
linprocfs on /usr/compat/linux/proc (linprocfs, local)
devfs on /var/named/dev (devfs, local)
procfs on /proc (procfs, local)


能大概解释一下/dev 下面文件夹, 怎么看系统硬盘个数和种类呢