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MultiMediaCard
Product Question  
CompactFlash® Why is the capacity of my flash memory card (as reported by many operating systems) different that the capacity that is listed on its label?  
Answer ID: 30 Created: 05/31/2004     Updated: 06/01/2004
For Products: Flash Memory -> ALL CompactFlash®
Flash Memory -> ALL CompactFlash® Type II
Flash Memory -> ALL Extreme™ CompactFlash®
Flash Memory -> ALL Memory Stick Duo™
Flash Memory -> ALL Memory Stick PRO Duo™
Flash Memory -> ALL Memory Stick PRO™
Flash Memory -> ALL Memory Stick™
Flash Memory -> ALL MultiMediaCard
Flash Memory -> ALL SmartMedia™
Flash Memory -> ALL Ultra CompactFlash®
Flash Memory -> ALL Ultra® II CompactFlash®
 
Category(s): Computer Only
PDA
 
 
Answer
Cause:

The operating system, when reading the size of the card, reports a slightly different capacity than what is listed on the card's label

Solution:

Definitions of a Megabyte:
1) Operating Systems commonly define a Megabyte (MB) as: 2 to the 20th power (1,024KB--Kilobytes).
2) DiskDrive and Flash Memory Card Manufacturers commonly define a MB as one million bytes (exactly 1,000,000 bytes).

Unformatted (Capacity)
Also known as drive byte capacity before formatting. The Maximum capacity of disk drive before formatting equals
[ (# Cylinders) X (# Heads) X (# Sectors) X (# Bytes per Track) ]

Example:
64MB CompactFlash Card consists of:
490 Cylinders
8 Heads
32 Sectors
512 Bytes per Track
This equates to: [ (490) X (8) X (32) X (512) ] = 64,225,280

Unformatted Capacity: 64,225,280 bytes
Formatted Capacity: 63,934,464 bytes (User Data)

Cause:
Disk Drive Companies such as STEK define 1 MEGABYTE as 1,000,000 BYTES. Operating Systems define 1 MEGABYTE as 1,048,576 BYTES (1024K X 1024K or 2 to the 20th power).

Example:
STEK 64MB CompactFlash Card being read by Microsoft Operating System.
STEK Total Formatted Capacity divided by 1 MB (as defined by the Operating System) equates to the following:
63,934,464 BYTES / 1,048,576 BYTES = 60,972,656 BYTES, 60.9MB displayed by OS.