Talk about What do you mean?, now you got me confused.
Since you didn't quote the message you answered, I assumed you were responding to me.
I now see you were continuing your previous post, i.e.
I attatched a 20x4 LCD, and write hex adress and hex data values 4 in 1 row like this : 00000000 00 00 00 00
If i read the bootsector ( 512 bytes ), it has only some values at the end, it has the 0x55 and 0xAA, and before that some more.
The rest all zeros.
The size in use after formatting is 2K, i overwritten 4 blocks and the card is still working in windows.
btw : i dont know if it matters, i format it with the SD to USB converter from my 3D-printer.
It is formatted FAT32, if i look in those library codes, it gives "invalid card" if the "bytes per sector" reads zero.
I need those "bytes per sector".
There are two layers here. One is the physical layer at which the SecureDigital card works. The other is the filesystem layer, FAT32 in your case.
At the hardware level, when writing to a SD cards, you write in 512-byte aligned blocks. This is often called a physical sector, because back when storage media had spinning disks, the smallest unit they could read and write was a physical sector (or more properly, a circular arc on the rotating media), usually also 512 bytes. (Nowadays hard drives with 4096 byte sectors are common, though; and on solid-state media like Flash, things are more complicated.)
At the filesystem level, FAT32 specifies a logical sector size. This is is a power of two, and at least 512.
FAT32 also specifies a cluster size. This is a power of two multiple of the logical sector size.
The typical logical sector sizes are 512 and 4096. The cluster size varies, but 32768 is most common. You can set either or both when formatting the filesystem, or let the utility implement some heuristic. Either way, these two numbers are described in the file system boot sector.
I don't know about Windows tools, but in Linux, if I want to find them out, I connect the media (via an USB card reader for SD cards), and then run sudo umount /dev/partition && sudo fsck.ext -nv /dev/partition, which tells me stuff like
fsck.fat 4.1 (2017-01-24)
Checking we can access the last sector of the filesystem
Boot sector contents:
System ID "MSDOS5.0"
Media byte 0xf8 (hard disk)
512 bytes per logical sector
16384 bytes per cluster
16448 reserved sectors
First FAT starts at byte 8421376 (sector 16448)
2 FATs, 32 bit entries
7577600 bytes per FAT (= 14800 sectors)
Root directory start at cluster 2 (arbitrary size)
Data area starts at byte 23576576 (sector 46048)
1892901 data clusters (31013289984 bytes)
128 sectors/track, 63 heads
8064 hidden sectors
60618880 sectors total
Checking for unused clusters.
Checking free cluster summary.
/dev/sda1: 1064 files, 57794/1892901 clusters
which tells me that this is FAT32 with 512 bytes per logical sector, and 32768 bytes (64 logical sectors) per cluster. The smallest block this FAT32 filesystem uses is therefore 32768 bytes; even a 1-byte file will reserve 32768 bytes on the media.
Hope this clarifies things a bit.