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Computer hardware problems Auto detect & hard disc drive parameters Enjoy playing with your computer’s CMOS setup? Well, watch out. If you change the hard disc setup from a “User” type to “Auto Detect”, the machine may no longer boot. Here’s why auto detect doesn’t always work. When you buy a new hard disc drive, one of the first things to do is to check the manual for the drive’s “parameters”. Alter­ natively, these parameters are usually also printed on a sticker attached to the drive itself. Your Drive parameters consist of: (1) number of heads; (2) number of cylinders; (3) number of sectors (4) landing zone; and (5) write pre­ compression. These parameters are required by the computer so that it knows how big the drive is and, more impor­tantly, where to go on the drive in order to retrieve data. For example, to retrieve a certain string of data, it may read sector 7 head 3 on the drive. That’s fine but what if you change the parameters of the drive, either intentionally or accidentally? This can easily happen if you install a new mother­board or transfer the drive to another comput­ er, for example. The most common error is using Auto Detect (in the system BIOS) on a drive that’s come from a machine in which it was “assigned” it’s para­ meters by the person who originally installed it. If it’s a boot disc, you may find that the machine will no longer boot up. Alternatively, if it’s a non-boot disc, you may no longer be able to retrieve files or the files may be corrupted, with lots of lost clusters. The reason for this is quite simple. Auto detect doesn’t actually read the settings that have been manually assigned to the drive. Instead, it re­ trieves the drive’s parameters by read­ ing the manufacturer’s data from the drive itself. Because of this, it follows that if the original manually-assigned para­meters differ from the parameters stored in the ROM, then using auto detect will cause data errors. This doesn’t matter if it’s not a boot drive and you no longer need the data that’s stored on it. In this case, you can just reformat the drive and carry on. The drive will be auto-detected each time you start the computer and all will be well. If it is a boot drive and/or you do need access to the data, then you will have to manually assign the required drive parameters if auto-detect causes problems. How do you know if it’s wrong or not? The most simple checks to do are: (1). Try to boot the machine. If the settings are incor­rect, the machine won’t boot (because it can’t find the system). Be sure not to run Scandisk with the autofix option, otherwise you could trash your data; (2). Run CHKDSK or Scandisk (no autofix) on the drive. This quickly checks the drive and if the settings are incorrect then you will receive hundred’s of errors. Parameter selection is very im­ portant. If you lose your parameters you can spend hours trying different combinations and still not guess the correct settings. My advice is to al­ ways write them down. Before leaving this subject, it’s worth noting that many BIOS’s offer two different auto detect options. The first is the auto detect in the BIOS setup. You activate this in or­ der to automatically enter the correct drive parameters in the main menu when it is first installed. You then save those parameters so that the machine doesn’t have to auto detect the drive each time it’s started. This is used for most computer setups and the detected parameters can be written down and stored with the computer (so that they can be later manually re-entered in a different setup if necessary). The other method involves select­ ing ‘Auto’ as the drive type in the main menu. This way, the system will auto detect the drive every time you start up. This is a simple way of installing drives, however you are generally not presented with the set­ tings. Only the size is shown so that if you transfer the drive to another machine without auto detect and you don’t know the settings, it can’t be correctly set up. Finally, I have seen different moth­ erboards return differ­ent para-meters for the same hard disc drive when using auto detect. Admittedly, this only occurs with some older mother­ boards; I haven’t encountered any modern motherboards that give this sort of problem. So be careful when playing with hard disc drives – it’s all to easy to lose your precious data and wind up with a door stop if you don’t know SC exactly what you are doing. March 1998  83