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[ The PC Guide | Troubleshooting and Repair Guide | The Troubleshooting Expert | Troubleshooting Specific Components | Troubleshooting Hard Disk Drives | Performance Issues ]

I added a new, modern hard disk to my older system, but it is performing slower than it should

Explanation: You upgraded or replaced your hard disk, but it is still performing at a speed comparable to your older drive. The transfer rate performance is not quite as good as you were expecting, or benchmarks are lower than what others are getting for the drive.

Diagnosis: As discussed in detail in this Reference Guide section on hard disk performance, the performance level of a hard disk is dependent on many different factors. Some of these are a function of the hard disk itself, but many are a function of the other parts of the system. Most hard disk benchmarks in fact are influenced by the speed of the chipset, processor, memory and other components. Also, putting a new hard disk into an old motherboard can greatly limit its performance because the interface may not be capable of running at the higher modes that are required for peak performance. Remember to check out this section in the Optimization Guide on hard disk performance.


  • Be careful about how you interpret benchmarks. In a nutshell, many benchmarks are deceiving and may give you an incorrect picture of how your hardware is really working.
  • Running a new hard disk on a system that uses ISA-based hard disk I/O will severely limit performance. I would strongly recommend a motherboard upgrade for any system that does not have at least a VESA local bus hard disk controller.
  • Many older systems do not support the faster PIO modes required for high-speed transfers to and from modern hard disks. In particular, if your system uses a 486 class motherboard and an expansion-slot hard disk controller, it may only support the slower PIO modes. In this case, the peak transfer rate of the hard disk will be reduced. You may want to upgrade to a newer controller or motherboard.
  • Some motherboards support higher PIO modes on their primary IDE channel than they do on their secondary channel. If the new drive is on the secondary channel you may see a speed increase by moving it to the primary. Consult your motherboard documentation.
  • Motherboards that do not support independent drive timing will slow down a faster disk if it is shared master/slave on a channel with an older disk. You may want to try the disk on a separate channel.
  • Make sure that the new hard disk is properly set up in the BIOS. Some systems may not set the disk to the optimum performance settings automatically, even when they autodetect a drive. You want to make sure that the PIO mode is set to the correct value, and also that block mode and 32-bit transfers are enabled (if the drive supports them and if they don't create any problems.)
  • Hard disks will generally just perform slowly on an older system overall. The hard disk's transfers are affected a great deal by the speed of the CPU and the motherboard, and a new, fast 2 GB drive is going to run much more slowly on a 486DX2-66 than it is on a Pentium 200, all else being equal.

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