The nand partitions layout in Samsung Galaxy S I9000 is controlled by a pit file (Partition Information Table), while for the mmc drive, it is hard coded in the init file.

For example, in Samsung Galaxy S I9000, the stock partition tables for s1_odin_20100512.pit should look like this:

NAND disk */dev/block/stl1 - stl6 omitted
device name	mount point	size in MB	remarks
/dev/block/stl7	n/a	7.5	known as KERNEL, for holding zImage
/dev/block/stl8	n/a	7.5	known as RECOVERY, for storing a copy of zImage
/dev/block/stl9	/system	286.5	known as FACTORYFS
/dev/block/stl10	/dbdata	134	known as DBDATA
/dev/block/stl11	/cache	35	known as CACHE
/dev/block/stl12	n/a	7.5	known as MODEM, for storing modem.bin

MMC disk
device name	mount point	size in MB	remarks
/dev/block/mmcblk0p1	/mnt/sdcard (/sdcard)	~6200 (8G) / ~14200 (16G)	none
/dev/block/mmcblk0p2	/data	~2000	none

For other pit files like s1_odin_20100513 and s1_odin_20100803, the size of /system and /dbdata are different. So for a larger /system partition, a smaller /dbdata and/or /cache will be resulted and vice versa since the total size of the nand is fixed (~500MB)

When we flash a rom to our phone, the above information will be read by odin to decide where the files will be stored. For instance, the zImage will be written to /dev/block/stl7 (/dev/block/bml7) and /dev/block/stl8 (/dev/block/bml8), while the FACTORYFS.rfs will be stored on /dev/block/stl9 (or /dev/block/bml9) at a specific start block address, up to the size of the file and so forth.

As a result, if we wanna use our own customized partition layout, we have to deal with the pit file and the mmc via fdisk or parted, etc


read more:
Free more available disk space from NAND - PART II
freeNANDmod - get more space from NAND - PART III
freeNANDmod - get more space from NAND - PART IV




for more details, read:
Investigation Into PIT Files
The reality of PIT files