Many times drives which are seemingly fine have already had this happen, however the host system is generally unaware that anything has happened and you’re able to continue on as usual. In some very new drives there can be up to four copies, so it can simply read the remaining code from the backup copy(s) then later during idle activities it’ll re-map the bad sectors from the SA to another unused part of the SA tracks. The whole process usually only takes a few seconds to complete.īut, what happens if the drive fails to read any part of the SA code that it really needs? Fortunately most drives have at least one backup copy of the SA code which is stored on a different platter surface (if there is more than one head). If you listen carefully to a healthy drive you’ll hear a small bit of grinding when it finishes spinning up as it reads the necessary bits of the service area code that it needs to get ready. That code is all stored on the platters, and many parts of the SA need to be read before the drive can become fully initialized and is ready to accept ATA commands (or SCSI commands in the case of enterprise drives). It also can hold vastly more information than the ROM which is necessary for the increasingly large ATA overlays and complex features that modern drives have.Ĭause #1 – When a hard drive is first powered on it doesn’t actually know how to even communicate with the computer it’s connected to. status, reallocated sector mapping, and even firmware updates done to the drive. Another useful reason for this area is that it can be modified by the HDD over time to handle things like changes in S.M.A.R.T. This area is generally inaccessible to the computer and user as it’s only used internally by the hard drive itself. The service area is stored in the negative tracks starting from track -1 (negative one) and is usually a few hundred tracks in length to something like -255. These tracks are numbered 0 to X (the max number for the model) and contain all the sectors of data that your computer normally has access to. Hard drive data is written in concentric rings starting from the outside moving toward the center. So the majority of the firmware code is actually stored in a specially designated area on the hard drive platters (disks if you will) called the “Service Area” or SA for short. Toshiba is the one exception here as they use larger memory storage on the PCB than others. However most modern drives are quite complex and require far more code than will fit on the typical ROM chip which only stores a few hundred KB of data. Also newer drives will have adaptive (calibration) data which is necessary to accurately read data from each read/write head. It’ll contain information about how many read/write heads the drive has and in what configuration. Some people erroneously call this the HDD BIOS, however this is only due to some poorly translated manuals from the past.Īll hard drives do have a ROM (read only memory) chip on the PCB (printed circuit board) that contains a bit of this firmware code which is necessary for the initial startup. Yes, hard drives require a certain measure of internal software which is generally referred to as firmware to function. They have a sort of CPU, RAM (though we call it a cache on a HDD), memory storage (ROM) and even….an operating system (of sorts). In fact many modern drives may actually have higher overall specs than your first computer you had in the early 90’s. Understanding HDD DesignĪ modern hard drive is actually very much like a full computer in itself. In this article we will speak in generalities that apply to most HDD’s however there are some variations with certain models such as Toshiba drives. To fully understand the clicking and how it can be addressed, you’ll first need to understand a few things about the design of most modern hard drives. The simple answer is that it’s what they are designed to do in certain situations. So Why Do Hard Drives Click When They Fail?
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