The BIOS Int 13h CHS barrier

As the BIOS Int 13h column shows:
 
  1024 Cylinders x 256 Heads x 63 Sectors x 512 Bytes/Sector
 
  = 8455716864 Bytes
 
So the theoretical BIOS Int 13h limit is 7.88GB (8.46 billion Bytes).

However, because DOS and other older operating systems cannot handle a 256^th Head, this becomes:
 
  1024 Cylinders x 255 Heads x 63 Sectors x 512 Bytes/Sector
 
  = 8422686720 Bytes
 
Thus the "real world" BIOS Int 13h limit of 7.84GB (8.42 billion Bytes).
 

    7.88GB is the limitation for how much drive space the BIOS Int 13h system call can access, using a CHS address (L-CHS). This is a BIOS specification limitation, and not a hardware or ATA (P-CHS) limitation. And while the BIOS can access the first 7.84 to 7.88GB on a larger capacity hard drive, all space beyond that should be accessed using LBA addressing. This requires a BIOS supporting the Extended Int 13h functions, and an operating system that can use LBA addressing; or an operating system that can bypass the BIOS by directly accessing a drive.

    For a multi-boot computer, using a large hard drive, any "legacy" operating system that uses CHS drive addressing as part of the boot process, may require that all files to load the operating system are kept below this BIOS Int 13h (7.84GB or 7.88GB) limit. See the 1024 Cylinder limit in the XOSL HOWTOs and FAQs for more details about that.