Specifications

Windows 137GB Capacity Barrier Version 1.0
6 7-Mar-2003
binary (base 2) this is 1111111111111111111111111111
2.
In hexadecimal notation this is
FFFFFFFh. In ordinary decimal notation it is 268,435,455. If each LBA is 512 bytes then this
represents a maximum addressable capacity of 137,438,952,960 bytes or 137GB.
ATA-6 defines 48-bit Addressing and opens a new higher limit that will carry storage capacities
far into the future towards a theoretical maximum of 144 petabytes.
Various sources refer to the 137GB limitation by different names. For example, it may be called
the 28-bit limitation. Likewise, if the focus is on the solution, the discussion may be about ATA-6
or 48-bit Addressing. In all cases, the issue is about ATA interface disc drive that are greater
than 137GB and the subsequent hardware and operating system support elements required to
achieve full capacity.
Note: Windows Explorer properties and some BIOS displays may represent the drive capacity as
131,073MB using a divisor of 2
20
or as 128GB using a divisor of 2
30
.
Solutions exist!
New systems can be built with full 48-bit support in both the BIOS and operating system.
Upgrading a legacy system, on the other hand, will require a little more effort than in previous
upgrade cycles to larger hard disc drives. Fortunately, solutions exist to add 48-bit addressing to
these systems. Some, but not all, of the solutions may require additional expense for OS updates
or hardware products to reach the goal of supporting ATA interface disc drives greater than
137GB.
WARNING: There is a HIGH RISK OF DATA LOSS if a partition on an ATA drive is greater than
137GB and 48-bit addressing support is not installed. Seagate is not responsible for
lost data. Without proper support, writing or saving data past the boundary line will
wrap around to the front of the file system and overwrite all of your file system
information, effectively erasing your drive. The following situations can result in data
loss:
 Moving a large drive from a 48-bit compliant system to one that is not
 Booting to a CD or floppy without 48-bit support
 Re-installation of the Windows operating system without upgrading the Service
pack or other required device drivers.
Motherboard and BIOS Considerations
Most motherboards have built-in connectors for the hard drive and CD-ROM drives. 40-pin
ribbon cables connect the drives to the motherboard. These motherboard connectors are often
labeled IDE Channel 0 and Channel 1. They are also called Primary Port and Secondary Port.
Both are the same. The system BIOS auto-detects the hard disc drive and issues an inquiry to
get the drive's number of LBAs. The largest number it is prepared to receive may be 137GB. In
this case you might check with your system manufacturer for a BIOS upgrade. Many name-
brand systems have the ability to "flash" the BIOS with new firmware. This process varies in
difficulty and is optional.
Alternatively, BIOS support for ATA>137GB can also be accomplished by putting the necessary
boot code on the disc drive itself. This small bit of programming emulates the BIOS support so
that when the higher-level operating system drivers begin to launch they can "see" the full
potential capacity of the drive. Seagate provides hard disc installation software called DiscWizard
to help with this task. DiscWizard writes boot code called a DDO on discs that do not have native
BIOS support for the full capacity of the drive. DiscWizard only writes the DDO when required.
Note: It is a common misconception that the DDO is some kind of memory resident program or
that it has the potential to slow disc access by being in memory. Like all BIOS routines, the
DDO is discarded from memory after about 5 seconds into the launch of the operating