Hard Drives definitions

After having passed over a few of the different technical terms in the tutorial, there is still a point that needs to be made. Why the capacity is displayed under Windows or any other operating system never the same as what your hard drive advertises it to be'
Before answering this, it is useful to remember that the language used in computers is binary, which can only have one of two states, 0 or 1. To represent the storage capacity, we use the “bytes” measurement unit which represents 8 bits (binary digit). Unlike what a lot of people may think, the kilobyte doesn’t represent 1000 bytes, but instead 1024 bytes (2¹⁰ bytes). The manufacturers have chosen to count 1000 bytes as a kilobyte, surely for simplicity, or possibly even for marketing reasons.

So, taking this as an example, a 200 GB disk that is commercially sold as this size is in reality:
1 giga-byte (GB) = 2 ³⁰ bytes which we will multiply by 200 giving us a total of 214 748 354 800 bytes. Using the “manufacturer’s logic”, the calculation base is not the same, as they consider:
1 giga-byte (GB) = 10⁹ bytes which is then multiplied by 200 giving us a total of 200 000 000 000 bytes, which in reality is the equivalent to: 200 000 000 000 divided by 2³⁰ bytes which gives a total of 186 GB. In conclusion, if you want obtain a real total of 200GB then you will need to purchase a hard drive that contains 214 748 364 800 bytes, or 215GB in the “manufacturers logic”.

Capacity: The quantity of data that can be stored on the disk.

Transfer Rate: The read/write rate of the data (Mbits/s).

Rotation Speed: The speed at which the platters turn, expressed in revolutions per minute (rpm/min). The speed of each hard drive caries from 4200 to 7200 rpm for 2 and a half inch disks and 7200 and 15000 rpm for 3 and a half inch disks.

Latency time: The time taken to change track which is linked to the rotation speed.

Seek Time: The average time needed for the head to position itself in the correct location to access the required data.

The shorter that this time is, the better the performance, but the access time advertised by the manufacturers is often the time needed for the read/write heads to move.

    

Radial Density: The number of tracks per inch.

Linear Density: The number of bits per inch on any given track.

Surface Density: Linked to the linear density and the radial density (bits per Inch2).

Memory cache: The memory cache allowing you to conserve the data that is most often accessed by the drive so that the overall performance can be improved.

Interface: This is the communication bus between the hard drive and the motherboard. The primary interfaces are IDE/ATA (P-ATA), Serial ATA, SCSI and SAS. You can also find eSATA, Firewire 400/800 as well as USB 2.0 for external hard drives.