Complex sentence: The first of these BIOS limits occurred when ATA drives reached sizes in excess of 504 megabytes, because some motherboard BIOSes would not allow C/H/S values above 1024 cylinders, 16 heads, and 63 sectors.
Split into simpler sentences: The first of these BIOS limits occurred when ATA drives reached sizes in excess of 504 megabytes. Because some motherboard BIOS would not allow C/H/S values above 1024 cylinders, 16 heads, and 63 sectors.