IDE Training Course, Part 1: A Detailed Look at the Basics and Technology

Saturated Capacity: Int13h Extensions And LBA

Usually, the data on a hard drive are accessed with the help of three parameters: cylinder, head and sector. However, this is only possible to a certain degree, as access takes place via the graying Interrupt 19 (13h in hexadecimal notation). This Int13h, however, needs the exact positional data to be able to access the data. It has 24 bits to do so:

  • 10 bits for the cylinder number (up to 1024);
  • 8 bits for the number of the head (up to 256);
  • 6 bits for the number of the sector (63, as numbering begins with 1 instead of with 0).

If you do the math based on 512 Bytes per sector, you'll get a total of some 16.5 million sectors, which is equivalent to 7.88 GB (8.46 GB if you base your math on 1,000 Bytes per kB).

Since there isn't a whole lot you can do with that nowadays, the Int13h had to be expanded. A simple change (for example, from 24 bits to 32 bits) would have meant that none of the old drives could have been addressed - thus a transparent expansion of the instruction set hat to be created.

With the help of the Int13h extension, addressing is increased to a full 64 bits (equaling 9.4 billion teraBytes); however, not only the BIOS but also the operating system must be able to deal with this new operating mode and address the drive accordingly, as long as it registers as an Int13h extension device. Logical Block Addressing, known as LBA mode, handles the necessary conversion of the drive geometry. In the end, it is still addressed using the CHS method (cylinder, head, sector), but LBA enables easier access via numbered sectors.

Guaranteed Safe: SMART

No, this term does not denote a hip compact car, but rather a sort of intelligent early-warning system. SMART, Self-Monitoring Analysis and Reporting Technology, permanently gets values from a modern hard drive's several sensors.

We generally differentiate between two types of operational failure: predictable and unpredictable errors. The latter simply occur every so often, and there's nothing you can do to prevent them (for example, the sudden defect in a chip). One example of predictable failure would be damage to the spindle motor. If you monitor the temperature of the spindle motor bearing or the time it takes to spin up, you'll be able to detect unusual behavior days, or even weeks before the failure - in a case like this, SMART would sound an alarm during boot-up. Ideally, the user still has time to save all important data to another storage medium.

The monitoring scope may vary from drive to drive. The most common, however, includes the following factors:

  • Number of Remapped Sectors
    Remapping takes places if sectors on the hard drive are about to crash, in which case backup sectors are available to compensate for the loss in capacity. Disadvantage: there's a slight drop in performance.
  • Max. Headroom
    How far away are the read/ write heads from the surface? If the distance is small, then this may presage a head crash.
  • ECC Error Count
    Records the number of encountered or corrected bit errors. An increasing number may indicate a lingering defect.
  • Temperature
    An increase in the drive temperature may be a sign of problems with the spindle motor.
  • Data Throughput
    An inexplicable reduction in the transfer rate may also be caused by a defect.

Even if your BIOS doesn't provide SMART support, most of the time you can determine your drive's status using software provided by the drive manufacturer or with system tools like Norton Utilities.

Our recommendation: if BIOS or another diagnosis software sounds SMART error messages, stop using the affected drive as soon as you possibly can and contact the manufacturer's support hotline. If your drive is still under warranty, you most likely won't have a problem exchanging it.