Haiku does not use driver letters. Volumes (partitions) are generally mounted as “/name-of-volume” in a Unix-like unified filesystem hierarchy starting at root (the first ‘/’). Your mounted volumes are shown to you as icons on the Desktop, like in Mac OS. There’s no Windows-like “My Computer” folder.
The boot volume is mounted as /boot and symlinked to as /name-of-boot-volume -> /boot. For now Haiku is a single-user system and your user/home folder is at /boot/home.
Unlike in classic Unix/BSD/Linux, the Haiku filesystem root folder (/) is virtual, non-persistant, essentially a small RAM-memory backed filesystem, as opposed to a disk backed (physical) filesystem. It can not hold any files, but only mount-points (of other disks or filesystems) and symbolic links (into these other filesystems).
A few links such as /bin, /etc, /tmp and /var exist to provide some Unix-similarity, to ease porting of Unix/Linux/Posix software. (The Haiku desktop/filemanager/filepanels don’t go as “low” as the root filesystem, in effect hiding it, so these legacy folders are not visible to most casual users, unless you open a Terminal/bash shell. The desktop/filemanger/filepanels instead present your desktop folder as the supposed root, if you go up one folder past your boot volume.)
Apart from the rootfs, which primarily exists to hold the other filesystems, two more virtual filesystems exist by default in Haiku: /dev and /pipe. These provide an interface to kernel services such as hardware access, networking, pipes and stuff you might need as an application programmer or a shell script user.
Try Haiku and run “df” in Terminal, or “ls -l /”
/boot/home> df
Mount Type Total Free Flags Device
---------------- -------- -------- -------- ------- --------------------------
/ rootfs 0 0 ------W
/dev devfs 0 0 ------W
/pipe pipefs 0 0 ------W
/boot bfs 30941188 23106212 QAM-P-W /dev/disk/ide/ata/0/master/0/0_0
/Haiku bfs 27655896 27536244 QAM-P-W /dev/disk/ide/ata/0/master/0/0_1
/Knife bfs 31784600 31774100 QAM-P-W /dev/disk/ide/ata/0/master/0/0_3
A listing of /
boot
Extacy -> /boot
Haiku
Knife
bin -> /boot/beos/bin
etc -> /boot/beos/etc
system -> /boot/beos/system
tmp -> /boot/var/tmp
var -> /boot/var
dev
pipe
To the application programmer, there’s a system provided C++ API called the Storage Kit, which includes the BVolumeRoster which lets you enumerate volumes and subscribe to mount/unmount events.
http://beunited.org/bebook/The%20Storage%20Kit/VolumeRoster.html
Another part of the “BeBook” describes the BeOS (and Haiku) filesystem architecture:
http://www.beunited.org/bebook/The%20Storage%20Kit/topic_Architecture.html