* A disk is divided up into **partitions** which are subsections of the overall disk. The kernel presents each partition as a [block device](./Devices.md#Devices.md) as it would with an entire disk.
* The disk dedicates a small part of its contents to a **partition table**: this defines the different partitions that comprise the total disk space.
* The **filesystem** is a database of files and directories: this comprises the bulk of the partition and is what you interact with in [user space](./User_Space.md) when reading and writing data.
Whenever you install a Linux distribution on a real or virtual machine, you must partition the drive. There are three main tools to choose from: `parted`, `g(raphical)parted`, `fdisk`.
The two tools disclose that the main harddrive is `/dev/nvme0n1` (equivalent to `sda` on older machines running Linux) and it has the standard three partitions:
* This takes up the smallest amount of space and exists in order to bootstrap the operating system: to load the kernel into memory when the machine starts. This is where your bootloader is stored and that will be accessed by the BIOS. In Linux this will be GRUB.
* This is the domain of the [superuser](./User_Space.md#root-user-superuser). The part of the filesystem that you need sudo priveleges to access and where you manage users
In the Linux world there are two main types: MBR and GPT. The type of table used determines how the OS boots. So although partition tables are also responsible for the partitioning of non-bootable sectors of a disk, **they are distinguished by the boot system they implement**.
If we look at the output from `parted` and `fdisk` above we see that the harddrive uses the GPT partition type.
#### Primary, extended and logical partitions
Most standard partition tables allow for primary, extended and logical partitions. The primary partition is the part of the harddisk that contains the operating system and is thus described as 'bootable' and may be called the 'boot partition'. During the bootstrapping process this is injected into memory as the [kernel](The_Kernel.md).
The extended partition is basically everything other than the primary partition. This is typically subdivided into other partitions that are called *logical* partitions. This is because they physically reside in the same sector of the disk (the extended partition) but are treated as virtual and independent disks.
In our example above:
*`/dev/nvme0n1p1` is the primary/boot partition
*`/dev/nvme0n1p2` and `/dev/nvme0n1p3` comprise the extended partition and by themselves are each logical partitions.
To demonstrate the process of partitioning a harddrive I am going to repartition an external SATA drive as if it were being primed for a fresh Linux install.
Let's take a look at the disk in its current form:
```
$ fdisk -l
Disk /dev/sda: 465.74 GiB, 500079525888 bytes, 976717824 sectors
Disk identifier: 9993F1BB-626C-485F-8542-3CC73BB40953
Device Start End Sectors Size Type
/dev/sda1 40 409639 409600 200M EFI System
/dev/sda2 409640 976455639 976046000 465.4G Apple HFS/HFS+
```
(This disk was previously used as a backup disk for MacOS so in addition to the extended partition which has a proprietary file system type (Apple HFS) it has a primary partition which would load the recovery OS. In contrast to my main harddrive this uses the standard SCSI prototcol and thus the partitions are prepended with `sda`.)
> Whilst we have created our partitions we cannot yet mount them. This is because we have not yet set up a filesystem on the partitions. This is the next step.
We cannot yet mount or interact with the partitions we have created. This is because we have not added a filesystem to each partition.
> A filesytem is a form of [database](/Databases/Basic_database_concepts.md); it supplies the structure to transform a simple block device into the sophisticated hierarchy of files and subdirectories that users can understand.
Linux recognises many types of filesystems. The native Linux filesystem is the **ext4** (Fourth Extended Filesystem). Another common filesystem is **FAT** (File Allocation Table). Instances of this include _MSDOS_,_EXFAT_,_FAT-32_. They originate from Microsoft systems
### Creating a filesystem
Remember we have two partitions on our external drive: `sda1` and `sda2`. We are going to use the `mkfs` utility to create an EXT4 system on both.
We can now mount our filesystems. Whem we mount, we must specify the following criteria with the request:
* The name of the device we want to mount.
* This will be the name or the partition. However the names (`sda` etc) assigned by the OS can change. In these cases and with GPT-based partitions you can use the UUID.
* The filesystem type (optional)
* The **mount point**
* This is the place within the existing filesystem where you want to mount the partition.
* When you mount to a directory, this directory _becomes_ the disk you have mounted, you will not see it as a subdirectory within the the mount point, you will just see the contents of the disk itself
Our `sda1` partition is now mounted at `mountpoint`. We can go ahead and create files. If we now look within the graphical file manager when we click on the `sda1` volume, we will see the new file we have created in `mountpoint`.
BIOS and UEFI are both firmware that is installed directly on the motherboard of the computer. They are firmware because they are software that is permanent and programmed into read-only memory.
In the context of disks, their most crucial role is locating the operating system on the harddisk and loading it into memory so that the bootstrapping process can begin. However they are also responsible for the computer clock and the management of peripherals.
As we can see from the `fdisk` readout, the boot partition uses EFI, the storage partition associated with UEFI.
Whilst UEFI is installed on the hardware, most of its configuration is stored in the EFI partition on the disk, whereas with BIOS, everything is on the chip. This make booting faster with UEFI.
Even though most modern computers use UEFI, it may still be referred to as BIOS for user-continuity. This is like on Windows. With Linux you have to explicitly create your boot process so the two are clearly distinguishable.
