Primary as you cannot boot from a logical partition.
Beginning.
Swap file allows allocating a small amount of Hard Drive space that can be used to Supplement RAM. This portion o the HDD will be used as additional RAM to your actual RAM.
Logical and extended partitions are derivatives of the (legacy) MBR [master boot record] disks. They refer to a virtual partition that exists in the extended physical partition of a drive. The only thing that limits the size of a logical partition and how many you have is the extended partition and its size on the drive.
GPT [general or generic partition table] disks can have an unlimited number of primary partitions, making logical and extended partitioning really only good for virtual machines, if you wanted a dedicated partition for that.
Primary partitions are the only partition capable of having the boot attribute set for the bios to utilize. As aravisian said, primary partitions are the only bootable partitions.
You can place home and any data partitions in extended. Efi, swap and system partitions must be primary.
If your not sure which type of disk you have, while in windows or zorin open the partition manager (gparted or disks in zorin). There will be a little label next to each partition, either primary and extended or basic and extended or logical. Basic is an MBR label. Another way is if there is an efi partition in the many you have. If not, you are running a legacy disk.
I always wonder about this statement as it smacks of the square root of two.
Logic dictates that there is a limit, as there is a finite space available on the drive. There is a finite space in which the minimum amount of data can be applied, therefor, partitions cannot infinitely shrink to accommodate unlimited partitions.
You could create a 100 100mb logical partitions and the bios, os and drive would be fine with it. You wouldn't be able to save much in each... but more than possible. Just because you can have unlimited partitions doesn't mean you need that capability.
If you had an EB (exobyte...1000TB) drive... then we're talking.
Ok... but that does not explain the physicality of how it can be Unlimited (Or infinite).
Compared to Grahams Number, 100 is the same value as 1.
Compared to Infinity, Grahams Number is the same value as 1 (Though P.o.I., infinity is not a number.)