2 GB IDE Western Digital Caviar AC22000: Capacity Issues

Power Computing provided the information in this article and it was deemed accurate as of 14 November 1997. Apple Computer, Inc. is not responsible for its content. This article is being provided as is and will not be updated in the future.

The 2 GB IDE Western Digital Drive is not reported by the MacOS or formatting utilities as a 2 Gigabyte disk drive. The discrepancy between the MacOS and the advertised capacity of 2 GB is result of the differences between how the hard drive industry calculates and advertises GIGABYTE designations and the way the Mac OS and other utilities calculates hard drive sizes. The MacOS reports the capacity after formatting. The configuration log included with PowerBase machines lists the drive as 1.9 GB, as the Mac OS Finder does. Until the configuration sheet is modified by manufacturing to explain that the value is a formatted capacity, a special addendum will be attached to the configuration log explaining the discrepancy.
When using the Mac OS or formatting utilities to calculate the available space on the 2 GB Western Digital IDE drive, the utilities will show the size to be approximately 1.9 GB (Gigabytes).

RESOLUTION
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After formatting, disk driver and other formatting information is written to the drive. This data reduces the available free space on the drive. Before formatting, the drive capacity is 2 Gigabytes.

The 2 GB IDE drive has a capacity of 2,000,388,096 bytes after formatting. The Mac OS and other utilities use a 'base 2' calculation when determining available space using the formula:

Total Bytes / 2^n where n = 30.

The Mac OS and other utilities round the calculated result to 1.9 GB for the 2 GB IDE drive. This is a formatted capacity value.

Western Digital advertises the Caviar AC22000 as a 2 Gigabyte drive. The drive capacity AFTER formatting is 2 trillion bytes (exactly 2,000,388,096 bytes), which is less than 2 gigabytes. This is equivalent to the 1.9 GB as calculated by the formula above. The advertised capacity is based on the total data storage space available on the drive, including formatting information.

Both numbers are equivalent. Before formatting the drive has the capacity to hold 2 Gigabytes worth of information. After formatting, this capacity is reduced and is calculated by the Mac OS as 1.9 GB.


Machines Affected: PowerBase
Published Date: Feb 20, 2012