Size of HDD ??

  Petesilver 18:01 24 Nov 2007

recently bought an Iomega USB HDD 320GB for extra storage can anyone explain why it only shows the capacity as 298GB where have to other 22GB gone ??
Its not that i need it but it seems wrong to sell it as a 320gb.....but i expect there is some simple explanation ??

  bremner 18:10 24 Nov 2007

Manufacturers shows the size with 1000 bytes being a Kilo Byte when it is in fact 1024. Carry that through and your 320GB drive is in fact 298.

The math is 320,000,000,000,000 /1024/1024/1024 = 298

  Fruit Bat /\0/\ 18:11 24 Nov 2007

Capacity measurements
A disassembled and labeled 1996 hard drive.
A disassembled and labeled 1996 hard drive.

The capacity of an HDD can be calculated by multiplying the number of cylinders by the number of heads by the number of sectors by the number of bytes/sector (most commonly 512). On ATA drives bigger than 8 gigabytes, the values are set to 16383 cylinder, 16 heads, 63 sectors for compatibility with older operating systems. It should be noted that the values for cylinder, head & sector reported by a modern drive are not the actual physical parameters since, amongst other things, with zone bit recording the number of sectors varies by zone.

Hard disk drive manufacturers specify disk capacity using the SI prefixes mega, giga, and tera and their abbreviations M, G and T, respectively. Byte is typically abbreviated B.

Operating systems frequently report capacity using the same abbreviations but in reference to binary-based units. For instance, the prefix mega in the context of data storage can mean 220 (1,048,576), which is approximately equal to the actual value of the SI prefix mega, 106 (1,000,000). Similar usage has been applied to prefixes of greater magnitude. This results in a discrepancy between the disk manufacturer's stated capacity and the apparent capacity of the drive when examined from the operating system. The difference becomes much more noticeable in the multi-gigabyte range. For example, Microsoft Windows reports disk capacity both in decimal-based units to 12 or more significant digits and with binary-based units to 3 significant digits. Thus a disk specified by a disk manufacturer as a 30 GB disk might have its capacity reported by Windows 2000 both as "30,065,098,568 bytes" and "28.0 GB" The disk manufacturer used the SI definition of "giga", 109 to arrive at 30 GB; however, because the utilities provided by Windows define a gigabyte as 1,073,741,824 bytes (230 bytes, often referred to as a gibibyte, or GiB), the operating system reports capacity of the disk drive as 28.0 GB.

HD manufacturers define 1 gigabyte as 1,000 megabytes. Windows defiines 1 gigabyte as 1,024 megabytes

oops too slow

  terrym 18:13 24 Nov 2007

I think the loss is to do with part memory been used by the machine to operate the new device but a loss of 22GB seems a bit much.

  terrym 18:14 24 Nov 2007

oooopppppps way too slow too!!!

  DieSse 20:44 24 Nov 2007

If you right click on the drive in My computer, and select Properties, you see the capacity in

Bytes - shows 320,000,000,000 (or thereabouts) - this is the 320GB that the manufacturer is referring to.

GB - shows 298 (or thereabouts) - which is what Windows reports the capacity as.

Both are correct - Fruitbats link and explanation shows the detail well.

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