README.md

@@ -6,14 +6,31 @@ Helper script to install Arch Linux with ZFSBootMenu from within a running Arch
 
 We expect minimal prep on your end. Please make sure that before execution the following conditions are met.
 
+### UEFI
+
+On a UEFI system ensure these conditions are met. See [How to prep](#how-to-prep) for details on how to meet these conditions.
+
+- One GPT-partitioned disk
 - Arch Linux live CD ISO image sees exactly one partition with partition type code `BF00` ("Solaris root")
 - Arch Linux live CD ISO image sees exactly one partition with partition type code `EF00` ("EFI system partition")
 - The `EF00` EFI partition is mountable, in practical terms this usually only means it has a file system.
 - No ZFS zpool exists
 
-### How to prep
+### Legacy BIOS
 
-On a blank example disk `/dev/sda` you can fulfill the requirements (One `EF00` partition with a file system plus one `BF00` partition) for example like so:
+If you are instead running a legacy BIOS machine ensure these conditions are met. See [How to prep](#how-to-prep) for details on how to meet these conditions.
+
+- One MBR-partitioned disk
+- Arch Linux live CD ISO image sees exactly one partition with partition type code `BF` ("Solaris root")
+- Arch Linux live CD ISO image sees exactly one partition with partition type code `83` ("Linux")
+- The `83` Linux partition is mountable, in practical terms this usually only means it has a file system.
+- No ZFS zpool exists
+
+## How to prep
+
+### UEFI
+
+On a blank example disk `/dev/sda` you can fulfill the UEFI requirements (One `EF00` partition with a file system plus one `BF00` partition) for example like so:
 ```
 sgdisk --new '1::+512M' --new '2' --typecode '1:EF00' --typecode '2:BF00' /dev/sda
 mkfs.vfat /dev/sda1
@@ -37,6 +54,28 @@ NAME         MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
 └─/dev/sda2 202:2    0   9.5G  0 part
 ```
 
+### Legacy BIOS
+
+For a legacy BIOS machine you'll be using a master boot record (MBR) on your disk.
+```
+printf -- '%s\n' 'label: dos' 'start=1MiB, size=512MiB, type=83, bootable' 'start=513MiB, size=+, type=bf' | sfdisk /dev/sda
+mkfs.vfat /dev/sda1
+```
+> `label: dos`: Create the following partition layout in a master boot record.
+>
+> `start=1MiB, size=512MiB, type=83, bootable`: Partition 1 begins 1 Mebibyte after disk start and is 512 Mebibyte in size. We're setting its bootable flag and setting partition type code `83` ("Linux").
+>
+> `start=513MiB, size=+, type=bf`: Partition 2 begins right at the start of Mebibyte 513, this is the very next sector after the end of partition 1. It takes up the remaining disk space, we're assigning type code `bf` ("Solaris").
+
+The result will be something like this at which point you can start the `setup.sh` script, see [How to run this?](#how-to-run-this) below for more details.
+```
+# lsblk --paths --output 'NAME,SIZE,FSTYPE,PARTTYPE,PARTTYPENAME,PTTYPE' /dev/sda
+NAME         SIZE FSTYPE PARTTYPE PARTTYPENAME PTTYPE
+/dev/sda      10G                              dos
+├─/dev/sda1  512M vfat   0x83     Linux        dos
+└─/dev/sda2  9.5G        0xbf     Solaris      dos
+```
+
 ## ZFS dataset layout
 
 The script will create a single ZFS zpool `zpool` on the `BF00` partition with dataset child `zpool/root` which itself has one child `zpool/root/archlinux`, that's where Arch Linux gets installed. Parallel to `zpool/root` it'll create `zpool/data` with a `zpool/data/home` child dataset that gets mounted at `/home`.