Hard Drive - why is 2 TB only 1.8 TB ??

whs said:

Buddahfan said:

whs said:

20 Gigabytes worth?

If you have a hard drive that is a a couple of yottabytes you might 20 Gigabytes worth:)

Where is such a yottabyte drive on sale?

see here

Sorry, Buddahfan, with all due respect, 99.9999 percent of the discrepancy one sees from buying a 2 TB drive and only realizing 1.8 TB is from the mathematical conversion, as has been mentioned here at least ... what ... 20 times ...

I believe you're thinking of sector use and actual storage capacity based on individual file sizes. That will not change the reported size of the HD.

mikedl said:

..the discrepancy one sees from buying a 2 TB drive and only realizing 1.8 TB is from the mathematical conversion, as has been mentioned here at least ... what ... 20 times ...

Or 15 in new money

Buddahfan said:

Also, hard drives come with some amount of built in "firmware" that uses a certain amount of the drive reducing the amount of space available to the user.

Well, it's not worth several GB for sure.
It's true that there is a reserved space on disks (to store SMART data for example, or to hold spare sectors for re-allocations), but it doesn't influence the actual disk size by the big difference you mean.

I think that the producers are right to say a disk with 1,000,000,000,000 bytes is a 1TB disk.
At least, the kilo, mega, giga, tera prefixes are used to refer to 10^x bytes (for the sake of ease, probably, rather than to try fooling the acquirers).

If you want to know the exact size of the disk, you better rely on gibibytes instead of gigabytes. I more or less use the method explained by p5bdkw to decide partition sizes myself.

whs said:

mikedl said:

Sorry, Buddahfan, with all due respect, 99.9999 percent of the discrepancy one sees from buying a 2 TB drive and only realizing 1.8 TB is from the mathematical conversion, as has been mentioned here at least ... what ... 20 times ...

I believe you're thinking of sector use and actual storage capacity based on individual file sizes. That will not change the reported size of the HD.

I think he got the idea - he just does not want to admit it. But in the meantime, we had some fun. :)

It does seem that it is some mathematical wizardry that is causing this difference

I just loaded "MiniTool Partition Wizard Home Edition" which I use to create and re-size partitions on my computers.

I have two hard drives, internal and external, on all of my computers.

I checked one of the computers which has a 500GB and a 1TB external, drive on it. The HDs are from different manufacturers.

For the 500GB hard drive MTPW is showing 465.8 GB
For the 1TB hard drive MTPW is showing 931.5 GB

So both drives are showing exactly 93.15% of the 500GB and 1TB.

So what is the mathematical wizardry that gets us to the 93.15% number.

Here is the answer.

This question comes up fairly frequently, and it doesn't have anything to do with the operating system. The problem is this: In Windows Explorer and other software applications, terms like megabyte and gigabyte refer to powers of 2, while in the hardware industry they tend to refer to powers of 10. One kilobyte in software is 2 to the 10th power, or 1,024 bytes. In hardware it's 10 to the 3rd power, or 1,000 bytes. The discrepancy mounts as sizes go up, as the table shows.
Take away 6.87 percent of your drive's stated capacity of 20GB and you get 18.6GB. If you could purchase a 1-terabyte drive, its actual capacity would be short by nearly a tenth of the capacity it would have had if measured in binary terabytes

Drive Capacity Discrepancy

1000/1024 = .97656.

.97656 to the 3rd power = 93.13%

Bingo - Resolved

Threads like this are why I love computer forums. Even an old goat like me can learn something new

The mathmatical part is a given, but one does have to wonder why drive manufacturer's continue to rate capacities as x1000 when the majority of use will be for OS's that use x1024 (which is the actual usable capacity). It strikes me that 'integrity in marketing' would dictate listing the 'user usable capacity' on the box.

Is there some valid reasoning behind this?

James

James Colbert said:

It strikes me that 'integrity in marketing' would dictate listing the 'user usable capacity' on the box.

Is there some valid reasoning behind this?

James

The reasoning is utterly valid.

"Integrity in marketing"

A non sequitur if ever I heard one and surely you jest.

Marketing 101 states that if 4 is good, then 5 is better.

If a 100 Watt stereo system is good, then surely a 200 Watt stereo system is better. Witness any audio retailer advertisement.

It follows that if 1000 is good, then 1024 is better, if .9313 is good, then 1.000 is better, and if 465 GB is good, then 500 GB is better.

Ad vomitum.

The measuring method is used because it is thought to be effective---a certain unknown percentage of rubes would shy away from a drive advertised at 465 GB and buy the adjacent drive measured at 500 GB, even though they have the same usable capacity.

The measuring method will be abandoned when it is thought not to be effective or when it is outlawed. Neither are on the horizon.

Can you imagine WD adopting the measuring method that yields 465 GB while Seagate continues to use the method that yields 500 GB? It won't happen as long as WD believes the rube census is greater than zero.

James Colbert said:

The mathmatical part is a given, but one does have to wonder why drive manufacturer's continue to rate capacities as x1000 when the majority of use will be for OS's that use x1024 (which is the actual usable capacity). It strikes me that 'integrity in marketing' would dictate listing the 'user usable capacity' on the box.

Is there some valid reasoning behind this?

James

Actually a 1 TB drive is only 1000/1024 to the fourth power so the available space in binary is only .9095TB.

So why does software show the available space as 931.5GB which is 1000/1024 to the 3rd power?

My guess is because it is easier to understand in GB which comes out to 931.35GB on a 1TB drive rather than showing drive size as .9095TB.

In addition to the non mathematically inclined .9095TB does not seem very large:):)

Hard Drive manufacturers use the SI Prefixes or the International System of Units

The International System of Units (SI) specifies a set of unit prefixes known as SI prefixes or metric prefixes. An SI prefix is a name that precedes a basic unit of measure to indicate a decadic multiple or fraction of the unit. Each prefix has a unique symbol that is prepended to the unit symbol. The SI prefixes are standardized by the International Bureau of Weights and Measures (IBWM)in resolutions dating from 1960 to 1991.[1] Their usage is not limited to SI units and many of these date back to the introduction of the metric system in the 1790s.
SI prefixes are used to reduce the number of zeros shown in numerical quantities before or after a decimal point. For example, an electrical current of 0.000000001ampere, or one-billionth (short scale) of an ampere, is written by using the SI-prefix nano as 1nanoampere or 1nA.

It could be a marketing thing.

The SI prefix is also correct in terms of metric prefixes which is easier for people to understand.

How Large is a Megabyte or a Gigabyte?

Disk Drive manufacturers have always used the more proper (you could even say correct or true) definitions of Mega and Giga in reference to the byte-capacity of their drives. Along with virtually all technical organizations in the world (including the Standards Board of the IEEE), they use the International System of Units (SI) which defines a Megabyte as exactly 1 x 10^6 bytes (1,000,000 bytes) and a Gigabyte as exactly 1 x 10^9 bytes (1,000,000,000 bytes). Of course, this doesn't mean that a sales blurb will give the exact capacity of an HDD (it may only be rounded up or down to the nearest one or two digits); usually the drive case will have a label giving the correct size in 512-byte sectors.

In contrast to the world of disk drives, Memory chip manufacturers had a basic problem with the SI prefixes, since electronic computer Memory has always been based on the Binary system! When computer Memory was rather small, engineers and technicians began to refer to a Kilobyte of Memory as the nearest value to 1 Kilo (or 1000) for a power of two. The differences were fairly easy to compute back then: A Kilobyte of Memory was not 1000 bytes, but rather 1024 bytes, since 2^10 is 1024. This became a bit more complicated when Memory sizes reached a "Megabyte" of 2^20 which is not 1,000,000 bytes, but rather 1,048,576 (1024 x 1024) bytes. Now there are hundreds of "Megabytes" of memory being used in home computers and even "Gigabytes" in large servers! These Binary "Gigabytes" of Memory are equivalent to 2^30 (or 1024 x 1024 x 1024 bytes) which gives us: 1,073,741,824 bytes.

The prefixes used on this page follow SI system usage; or will state specifically that they refer to the “Binary” (power of two) format. In time, people should eventually start to use the new terms MiB and GiB to represent Binary-Megabytes and Binary-Gigabytes (see the essay “Prefixes for Binary Multiples” ).

When I open Windows Task Manager it shows the amount physical memory as 3,838MB

1000/1024 to the second power (because it is shown in MB) times 4 =3,815MB

Difference of 23MB due to rounding:)