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[ The PC Guide | Systems and Components Reference Guide | Hard Disk Drives | Hard Disk BIOS and Capacity Factors | Hard Disk Size Barriers ]

The Phoenix BIOS 4.03 / 4.04 Bug (3.05 GiB / 3.28 GB) Barrier

This is another rather obscure size barrier, and one that differs from most of the others I have described in this area of the site. It is different because it is not due to any inherent BIOS design issue, nor due to an operating system limit or characteristic. It occurs due specifically to a programming error or bug in a few types of systems made in the mid-to-late 1990s. Some systems that use Phoenix BIOSes, versions 4.03 or 4.04, have a problem with the BIOS routine that calculates the size of hard disk drives. Note that BIOS code is initially written by the BIOS maker, and is subsequently tailored by specific system or motherboard manufacturers. This means that some specific implementations of these BIOS versions may not have this bug while others will.

This problem is also strange because the barrier actually isn't just a single value; it seems to depend on the values of the geometry parameters, and behavior can be different based on the values entered. Assuming standard IDE head and sector values of 16 and 63 respectively, the cylinder field can have a maximum value of 6,349 without any problems, resulting in a maximum capacity of 3.05 GiB or 3.28 GB. If a cylinder value of 6,350 to 8,322 is used the BIOS setup program may lock up. Cylinder values of 8,323 to 14,671 apparently work but the displayed drive size is incorrect.

Subsequent versions of this BIOS code have of course corrected this bug, which occurred several years ago. If you still have a system exhibiting this problem, you may be able to get a BIOS upgrade to correct the problem.

Next: The 8,192 Cylinder (3.94 GiB / 4.22 GB) Barrier


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