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Drive Capacity

Posted on 2004-10-12
Medium Priority
Last Modified: 2008-01-16
Based on this infomation how can I determine the hard drive capacity?
bytes per sector      512
sectors per track      63
cylinders      16383
heads      4
Disks 2
Question by:microcoop
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LVL 96

Expert Comment

by:Lee W, MVP
ID: 12294361
I believe it's
bytes per sector X sectors per track X cylinders X disks X 2
LVL 96

Expert Comment

by:Lee W, MVP
ID: 12294371
See This Link for some info:

Actually, here's your answer:

Author Comment

ID: 12294470
The hard part I am having is actually getting the right answer. This particular hard drive stated above is 160 GB. But I just don't come up with that answer.
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LVL 13

Expert Comment

ID: 12294588
You can't tell the size with those numbers, or at least not that I can tell.  That's the old method of determing size.  When drives got bigger and bigger they had to address them differently (hence LBA).  I wish I could find a website to point you to to describe this, but I haven't found one.


Expert Comment

ID: 12295367
is it just me or does that make it 4 terabytes (ref to first post) :P


Expert Comment

ID: 12295395
did you get this information from your bios???  your bios may not be able to see it all.  you could look on the hard drive itself to see the numbers, and if they are different from those already posted in the question, please update.

LVL 93

Expert Comment

ID: 12295450
bytes per sector     512
sectors per track     63   ---- 512 x 64 =  32768 bytes per track
cylinders     16383         ---- 32768 x 16383 =   536,838,144 bytes per platter
heads     4                    ----  536,838,144 x 4 = 2,147,352,576 == 2Terabyte
Disks 2

I assume here there are 2 platters with 2sides, counting for 4 heads in one drive.
Of course, if you have 2 drives, it doubles
LVL 12

Expert Comment

ID: 12296131
The size is 2.0GB

16383 * 4 * 63 * 512 = 2113800192 Bytes / 1073741824 (GB) =~ 1.97GB

If your drive is made by WD your can use it's diagnostics utility available for the download at the following link:


Author Comment

ID: 12296932
I am seriously confused now. The size of this drive is 160 GB, I just do not know how that number is reached. Here is all the info that I know. Can someone qrite out the formula and plug in the numbers to show how they reach 120GB.

Barracuda 7200.7
Formatted Gbytes (512 bytes/sector)  160
Interface Ultra ATA/100
Internal Transfer Rate (Mbits/sec) 683
Max. External Transfer Rate (Mbytes/sec) 100
Avg. Sustained Transfer Rate (Mbytes/sec) >58
Average Seek (msec) 8.5
Average Latency (msec) 4.16
Multisegmented Cache 2048
Spindle Speed (RPM) 7200
Discs/Heads 2/4
Bytes per Sector 512
Logical CHS 16383/16/63
Recording Method 16/17 EPRML
Contact Start-Stops 50000

LVL 12

Accepted Solution

zvitam earned 2000 total points
ID: 12297265
I Found the following explanations:


Shows that CHS (Calculation by Cylander Head and Sectors) is limited to 8.4GB.
 ( 16383 Cyl, 16 Heads, 63 Sectors - Which seagate manual actually states the manual avaible from the following URL:
 http://www.seagate.com/support/disc/manuals/sata/cuda7200_sata_pm.pdf   look on sections 2.2 and 2.3)


Explains LBA ( Logical Block Addessing) that is used instead of CHS.


Shows that CHS is no longer relevant for Calculating the disk size.

Hope that helps,


Expert Comment

ID: 12303677
2,147,352,576 is 2.147 gigabytes, not terrabytes, unless these are 1,000 byte "packages".

Author Comment

ID: 12304721

     You are exactly right. That is very confusing that the CHS equation is posted everywhere as the way to find capacity, but infact you can not use that equation for any hard drive over 8.4GB, which most are. It's also confusing that the hard drive manufacturers decide to use their own definition of megabyte and gigabyte instead of the true representation in base2.

So take the hard drive WD Spartan WD68AARTL
Cylinders 13176
Heads 16
Sectors/Track 63
Landing Zone 13176
WPC 13176
Jumper Setting Information Ten Pin Drive
Physical Specifications
Formatted Capacity* 6,800 MB
Interface 40-pin EIDE
Actuator Type Rotary Voice Coil
Number of Platters 1
Data Surfaces 1
Number of Heads 1
Bytes Per Sector 512
User Sectors Per Drive 13,281,408
Servo Type Embedded
Recording Method Rate 16/17 PRML
ECC Reed Solomon
Head Park** Automatic
* Western Digital defines a megabyte (MB) as 1,000,000 bytes and a gigabyte (GB) as 1,000,000,000 bytes

Then the CHS formula works here
i)      (13176 * 63*16*512)/ 1073741824 = 6.33 – True Gigabytes
ii)      (13176 * 63*16*512)/ (1024*1024) = 6485 – True Megabytes
iii)      (13176 * 63*16*512)/ 1000000000 = 6.8 – Declared Gigabytes
iv)      (13176 * 63*16*512)/ 1000000 = 6800 – Declared Megabytes

But for the above example Barracuda 7200.7
We need to use this formula

User Sectors Per Drive * Bytes Per Sector/ 1 073 741 824 bytes = Capacity in Gigabytes


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