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Windows 7: What determines partition type when formatting?

17 Jan 2020   #1

Windows 7 Enterprise x64
What determines partition type when formatting?

I work with a legacy device that does not recognize USB dongles formatted as FAT32 with LBA(partition type 0x0C). It only works with normal FAT32 with CHS(partition type 0x0B).

Most of the USB dongles I use are 4 GB, and they always get formatted as normal FAT32(0x0B) when i use the built-in Windows formatting tool. Recently I got a 16 GB USB dongle which after formatting ended up with partition type 0x0C. I also tested an 8 GB one, which correctly ended up with partition type 0x0B.

Does anyone know how the formatting tool determines which partition type to use? Does it depend on the size of the USB dongle, or some other hardware detail? I've been researching this via Google for a while now, but haven't been able to find any good info..

I know it is possible to change the partition type using the diskpart tool, but I am specifically trying to find USB dongles that end up with partition type 0x0B without any fuss.

Thanks in advance for any help!

My System SpecsSystem Spec
17 Jan 2020   #2

win 8 32 bit

Welcome to the forum. You can set partition type and format what you want normally USB drives will often come preformatted so it's simple for can re partition and format at any time.
My System SpecsSystem Spec
17 Jan 2020   #3

Windows 7/8.1/10 multiboot

Partition sizes were limited to 8GB under CHS addressing. Due to register size limitations, the values could range from C=0-1023, H=0-255, S=1-63. At 512 bytes/sector, that calculates out to a disk size of 1024*256*63*512, or about 8GB.

In an MBR-type partition table, partition size is expressed in both CHS and LBA terms, but when the partition is larger than 8GB the CHS values are "pegged" at their maximum values. The partition-type indicator of 0x0C is a flag telling the system and utilities to ignore the CHS values and use the LBA values instead.

It sounds like your legacy device is so old it only knows about the CHS registers of the partition table and not the LBA registers.
My System SpecsSystem Spec


 What determines partition type when formatting?

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