Partition naming is thanksfully simpler than drive one. Partitions are simply given a number from 0 up (decimal). Sometime a "p" is appended on front of the number:
cat /proc/partitions major minor #blocks name 8 0 488386584 sda 8 1 52436128 sda1 8 2 1 sda2 8 5 2104483 sda5 8 6 20972826 sda6 8 7 52436128 sda7 8 8 360434308 sda8 179 0 3979776 mmcblk0 179 1 3975680 mmcblk0p1
As you see, partition devices are listed in /proc/partition. This file... is not a real file but is created on the fly. Don't worry, for what we need it's a file.
Notice the "p1" partition name for the SDHC card.
Max number of partitions is 15 for SCSI and all the drives using the new SATA driver, 63 for IDE drives (0 is the full drive, 0 to 15 is four bits 0 to 64, 6 bits)
Not all the numbers have the same meaning. This mess come from the PC history. One can divide floppies with partitions, but then 4 ones seems sufficient. But then come Hard drives :-). So the partitons numbers 1, 2, 3 and 4 are primarypartitions. One drive can only have 4 primaries.
To go further, we have to use one of these primary as a big one and sub-partition this one, so to have logicalpartitions. The big extendedpartition can be any of the 4.
So, remember, the primary partitions are inside the drive and the logical partitions are inside one of the primary, called the extendedpartition.
Once the logical partitions are created, it's no more recommended to write directly to the extended one. Writing to an extended partition would erase the logical ones like writing directly to a hard drive erase the partitons. Beware, it's possible!!
If, after creating 4 primary partitions, all the disk space is not used, the remaining space is lost (unusable), so most of the time, create the desired primaries, then at last the extended one with all the remaining room.
It's not necessary to create 4 primaries. You could use only one extended (Linux only), but there are some advantages of using primaries.
Primaries being 4, the first logical partition is always 5. So any partition with number of five and up is a logical one.