If you are using a new harddisk (or want to wipe out the whole partition table of your disk), a new partition table needs to be created. The “Guided partitioning” does this automatically, but when partitioning manually, move the selection on the top-level entry of the disk and hit Enter. That will create a new partition table on that disk. In expert mode, you will then be asked for the type of the partition table. Default for UEFI-based systems is “gpt”, while for the older BIOS world the default value is “msdos”. In a standard priority installation those defaults will be used automatically.

If you have an existing other operating system such as Windows and you want to preserve that operating system while installing Debian, you may need to resize its partition to free up space for the Debian installation. The installer supports resizing of both FAT and NTFS filesystems; when you get to the installer's partitioning step, select the option Manual and then simply select an existing partition and change its size.

While modern UEFI systems don't have such limitations as listed below, the old PC BIOS generally adds additional constraints for disk partitioning. There is a limit to how many “primary” and “logical” partitions a drive can contain. Additionally, with pre 1994–98 BIOSes, there are limits to where on the drive the BIOS can boot from. More information can be found in the Linux Partition HOWTO, but this section will include a brief overview to help you plan most situations.

“主” 分割區是 PC 磁碟上最原始的分割區方式。但是，每個磁碟只能有四個主分區。為了突破這個限制，發明了 “延伸 (extended)” 以及 “ 邏輯 ” 分割區。將一個主分割區設定為延伸分割區，您可以將之分成許多邏輯分割區。每個延伸分割區最多可切割成 60 個邏輯分割區﹔但是每個磁碟只能有一個延伸分割區。

對於 SCSI 來說，Linux 限制每個磁碟最多有 255 個分割區( 3 個可用的主分割區，252 個邏輯分割區)。對於 IDE 來說可以有 63 個分割區( 3 個可用的主分割區， 60 個邏輯分割區)。但是通常 Debian GNU/Linux 系統只支持 20 個分割區裝置，因此您不能安裝超過 20 個的分割區，除非您先為這些分割區手動建立裝置檔案。

如果您有一個很大的 IDE 磁碟，既沒有使用 LBA 定址，也沒有 overlay 驅動程式 (硬碟製造商有時候提供此功能)，那麼開機分割區 (含有您核心映像的分割區) 必須放置在硬碟第一個 1024 磁柱內。(在沒有 BIOS 轉換的情況下，大約有 524MB)。

This restriction doesn't apply if you have a BIOS newer than around 1995–98 (depending on the manufacturer) that supports the “Enhanced Disk Drive Support Specification”. Debian's Lilo alternative mbr must use the BIOS to read the kernel from the disk into RAM. If the BIOS int 0x13 large disk access extensions are found to be present, they will be utilized. Otherwise, the legacy disk access interface is used as a fall-back, and it cannot be used to address any location on the disk higher than the 1023rd cylinder. Once Linux is booted, no matter what BIOS your computer has, these restrictions no longer apply, since Linux does not use the BIOS for disk access.

如果您有一個大硬碟，您也許必須使用磁柱轉換(cylinder translation)技術。它可以透過 BIOS 設定程式中設定，比如 LBA (Logical Block Addressing) 或者 CHS 轉換模式(“Large”)。關於大硬碟的各種議題討論可以在 Large Disk HOWTO 下找到。如果您正在使用一個磁柱轉換方案，而 BIOS 不支援高容量硬碟的存取，您的開機分割區必須放置在 轉換後 的 1024 磁柱內。

The recommended way of accomplishing this is to create a small (25–50MB should suffice) partition at the beginning of the disk to be used as the boot partition, and then create whatever other partitions you wish to have, in the remaining area. This boot partition must be mounted on /boot, since that is the directory where the Linux kernel(s) will be stored. This configuration will work on any system, regardless of whether LBA or large disk CHS translation is used, and regardless of whether your BIOS supports the large disk access extensions.