Which of the following commands overwrites the bootloader located on /dev/sda without overwriting the partition table or any data following it?

Without a count limit, dd will write 512-byte zero blocks continuously until the entire disk is overwritten, destroying all partitions and data.

A block size of 512 with count=1 writes a full 512 bytes, which includes bytes 446-511 containing the partition table entries and boot signature, corrupting the partition layout.

The x86 MBR layout reserves bytes 0-439 for bootstrap code (the bootloader), bytes 440-445 for disk signature and reserved space, and bytes 446-511 for partition table entries and the boot signature. Specifying bs=440 count=1 writes exactly 440 zero bytes, overwriting only the bootloader code area while leaving the partition table entries at byte offset 446 and beyond completely untouched.

Without count=1, dd will write 440-byte zero blocks indefinitely across the entire disk, destroying all filesystem data and partition structures beyond the first block.