Actual memory in storage device

[Kelvin]

I just bought a 1 terabyte desktop storage device. When plugged in the space shown on the disk was 931 gB. Now I know that devices may use some memory in running - but 93 gB? That's nearly the size of my 'c' drive!
Is this normal?

[ABerrant]

http://en.wikipedia.org/wiki/Gigabyte#Consumer _confusion

[Kelvin]

Excellent and very rapid reply ABberant, wear your stars with pride!

[VHG]

Computers use binary and counting tends to be grouped as follows:

2, 4, 8, 16, 32, 64, 128, 256, 512, 1024

This is why digital devices (like memory cards) are often 256 or 512 in size for example.

But when you get to 1024 people often show it as 1k.

Of course 1024 is very near 1,000, so when people talk about something being 1k (1 thousand) they actually mean 1024.

So if a file on your hard disk was said to be 1k it may actually be 1024 bytes and you have already "lost" 24 bytes.

So even at those low numbers you can get confusion between if 1k means 1,000 or 1024.

Now expand that to talk about megabytes, or gigabytes or terabytes.

When they say 1Tb do they mean 1Tb based on 1,000 or 1024?

So as that wiki article points out, disk makers talk about 500Gb disks or 1Tb disk, but tend to "round up" to keep it simple.

And that way you think you have lost a lot of your hard disk.

[magicmerlin]

I have to ask where you got the 93gb from?

1000-931 = 69

Answer is still the same whether its bytes or bananas.

[ABerrant]

In real money (not the marketing world) 1TB = 1024GB therefore 1024 - 931 = 93

[ACtheTROLL]

Disc mfrs work in denery - the rest of the computer world work in binary

so yes 1k = either 1000 or 1024

however that's not where the space has gone
when it's formatted the program creates a
a partition table - describes the size of the disc/partition
a master boot file - to say look at this drive for the boot files
a master file table (in dos was the fat)
to store files the disc is split into lots of little boxes
files are split into box sized chunks
each file uses the first box
the address of this box is stored in the mft database so it can be found later

if the file is big enough - it spills into more boxes
subsequent boxes are chained together each "next box" is added to the end of each data chunk so when the file is read the head jumps from one box to the net until it sees an end of file marker

the whole MFT is created during formatting
the size of the disc is used to calculate how many boxes can be created ... and how many entries the MFT will need

it then reserves part of the disk to be used as a database of where the start of each file you store is located. (this table is a fixed size - so it doesn't matter if you store 1000 1Gb files or 1000000000s of 1k files - the system will have reserved enough space to make entries available for both)

1Tb is pretty big - so the database has to be big
and so you loose a fair chunk of discspace to all the system files needed by the disc itself