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BIOS & Hard Disks

Advanced users

Not all of these will have been tested by THPC,




Record current settings before making any change

All BIOS versions are different. Likewise for hard disks models, even from the same manufacturer. Exercise extreme caution and attention if/when making any BIOS alteration that may affect the hard disk(s). Give suitable attention to the manufacturer's handbook, and fully research your own model(s).

Very often the BIOS settings are selected automatically by the BIOS if autodetect is set. It is usual (and recommended) for Autodetect to be set as this normally produces the best overall result (it's also the easiest!)

Sometimes, however, the optimal settings are not correctly set. Or it may be that the PC assembler has not taken the time to set it up for best performance. Having optimal performance from the hard disk(s) is essential to overall system performance so this should be investigated fully.

Don't jump to quick conclusions. For instance, if Autodetect has disabled a function you would expect Enabled, then perhaps there is a good reason, even if not immediately apparent. Or if Autodetect has Enabled Block Mode for one hard disk but not another, then it is probable that the second disk simply does not support that feature.

Never, absolutely never, try to force a hard disk to function with any setting higher than its manufactured specifications, for example setting PIO mode 4 when it is designed for PIO 2.


Many newer BIOS have a Block Mode feature

Hard disk sectors are transferred to memory during interrupts (minute pauses in activity).

Block Mode allows many hard disk sectors to be transferred on a single interrupt, an obvious speed enhancement in transferring data from the disk to memory.

Block Mode can usually be set to 16 or 32 sectors per interrupt. If yours is disabled, you can try enabling it to see if a performance gain results. If not, or of you encounter any problem(s), then turn if OFF.

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Your BIOS may not support large hard disks

Be cautious when purchasing very large hard disks if your system, and its BIOS, are relatively old. It may be that your BIOS does not support hard disks larger than a certain size - you may not have access to its full capacity.

You can still use these large disks though there may be a financial cost or performance deterioration. To gain access to the full capacity of your hard disk there are four options:
  • Get an BIOS upgrade that supports Translation (free - visit manufacturer's Web Site)
  • Upgrade to a new motherboard with an enhanced BIOS (costly, but there are other benefits)
  • Add an expansion card with an enhanced BIOS (costly)
  • Use a Software Translation Driver (free)

Translation Driver: The Translation Driver (or Dynamic Drive Overlay) is the most commonly used with older BIOSes and motherboards as a BIOS upgrade does not often have Translation support. It is also likely to be supplied free with the new hard disk. Best known are Disk Manager and EZ-Drive.

The Translation Driver resides in memory (a small footprint) and does the same BIOS translation that your BIOS does when you set it in extended CHS mode. Most of the time these drivers will work fine, especially if you are not doing anything too unusual with your PC.
Be sure the driver you use is customized for that hard disk model \ ....

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Potential problems with Translation drivers

You should be aware of some potential problems with Translation drivers:

Removing the Driver: This can be problematic. Use the uninstall that came with the driver. You will normally have to repartition and reformat the disks. Partition Magic will not help.

Booting from Floppy Disk: The initial part of bootup MUST be from the hard disk - you must wait until prompted and then put in the floppy - a small inconvenience.

Compatibility: Bus Mastering drivers are often not compatible with drives that are using a Translation driver. Older utilities can sometimes cause data loss.

Reduced Upgradability: There may be problems if you get another new hard disk. Your current Translation driver is customized for that manufacturer's drive only - stay with his model.

OS Installation: You can expect standard operating systems to recognize the Transition drivers. However you should verify that each operating system you install is capable of handling your driver. Non-standard OSs may be a problem. Win9x is fine.

Most often everything is fine. THPC has used the EZ-Drive Translation driver on an older P166 for some years without any problems (and using Win95, Win98, MSDOS 6 & 7, .... and Linux).

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Improve data transfer rates

Another feature offered by most newer BIOSes is 32-Bit Hard Disk Transfers.

This provides a small performance improvement when enabled via the BIOS.

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The IDE hard disk can be accessed in one of two ways

  1. DMA (Direct Memory Access - read DMA, UDMA)
  2. PIO (Programmed Input/Output)

Until recently, PIO has been the most commonly used. There are 5 different PIO modes, 0 (slowest) to 4 (fastest). It is to your advantage to ensure, all other things being equal, that the mode is set to the highest level the drive can handle.

Under most BIOSes the correct mode is detected automatically when Autodetect is enabled (recommended for most users). Most newer BIOSes support all the different PIO modes - the latest drives are mode 4.

In the majority of BIOSes the lower PIO mode has to be selected when two devices, capable of different modes, share the same channel. The only exception to this is when your system supports Independent Timing (so check it out if you have a recent BIOS).

  • Some BIOSes may not select the optimum mode for your device(s).
  • Keep similar devices on the same channel.
  • And never select a PIO mode higher than the drive is designed to handle.

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Please remember that you alone are responsible for the consequences of any changes you make to your computer hardware or software.

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