View Full Version : XP & Hard Disc Size

TABRJ

06-07-2002, 01:39 PM

I have just purchased a new computer with XP Home Edition. It was sold to me as having a 40.oGB hard drive. When I go START my COMPUTER and click on C: properties is says 32.6 Gb D: 4.6Gb giving a total of 37.2Gb. Q. Does XP take up the other 2.8Gb or is it a 37.2Gb hard drive?

Babe Ruth

06-07-2002, 01:54 PM

Hi Tabjr,

Most manufacturers sell harddrives as being e.g. 40GB but are actually 40,000,000,000 bytes when a 'real' 40GB would be 42,949,672,960 bytes.

So therefore taking your 40GB drive and dividing by a 'real' GB would come to 37,252,902,985 bytes or approximately 37.25GB.

Confused so are a lot of us!!

Cheers, Babe.

Heather P

06-07-2002, 02:27 PM

I've long forgotten the mathematical statistics behind disk sizes, but it all started with bits. There are 8 bits to a byte (a bit being a single 0 or 1). 8 bits are used to define 1 character (like an "a").

Trouble is, 8 doesn't divide nicely into 1,000. So 1Kb is actually 1024 bytes. For simplicity rounding takes place.

We meet rounding in other areas. Due to a lack of 1c coins $1.96 is charged at $1.95; A 1116cc engine in a car is refered to as 1100cc. For some reason computers round up.

TABRJ

06-07-2002, 03:08 PM

Thanks to you both. I now understand, well sort of. Many thanks :-)

Graham L

06-07-2002, 03:29 PM

Not exactly right Heather. It's all about powers of 2 or 10. 10^3 --> 1000, 2^10 --> 1024 ( 1 k ). 2^10 x 2^10 = 2^20 ( 1 MB). 10^3 x 10^3 = 10^6 (1 million).

A 3.5" floppy has 2880 sectors. Each sector is 512 (2^9) bytes -- 1/2 kB.

That makes 1.44 MB. How? Why? (Windows will format a floppy and say it has 1.36 MB). The "2880" is a decimal number. The "k" is a binary value.

IBM made the first hard disks. There were about 50 platters, each 24" diameter. They held (I think) 20 MB.

IBM decided at some stage that 1 MB was 1000 (decimal) kB (powers of 2 "k") . That has been the normal unit. MS have recently adopted the ISO standard,

But disk drive manufacturers will use whatever units will give the largest numbers in their advertising. They will often use the IBM unit. They might use the decimal million for even bigger numbers. They have stopped using the "raw" capacity --- unformatted size, because IDE drives are factory formatted. A 1.44 MB floppy is 2 MB unformatted: that's how MS can use a 1.7 MB format for their distribution disks.

"Lies, damned lies, and advertising." ]:)

Heather P

06-07-2002, 05:17 PM

Graham,

Did I mention that I've forgotten the actual maths behind it cause everytime I try to think about it I get a headache?

Essentially it comes down to the fact that we have 10 fingers so use the decimal system. Computers have only 2 states - on and off - so use the binary system.

Rather than explain the maths (which involves power to and square roots - headache forming stuff) the marketing people find the nearest whole number and round up to it.

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