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

I have a hard disk that is over 540 MB in size but the system is seeing it only as a 504 MB or 528 MB drive

Explanation: The system is not seeing the full size of your hard disk. In particular, the system is detecting the disk as being either 504 or 528 megabytes (depending on what piece of software is reporting the size). Other than this, the hard disk does appear to work.

Diagnosis: The maximum size of an IDE/ATA hard disk running in standard, untranslated mode is 504 binary megabytes, or 528 decimal megabytes. This is the classic barrier that limits the use of larger hard disks on older systems. In order to use a disk over 504 MB in size, you must have a motherboard or hard disk controller capable of BIOS translation, or you must use a dynamic drive overlay to do the translation in software. If your large disk is showing up as 504/528 MB, then this means that either your motherboard and BIOS do not have translation support, or that support has not been enabled.


  • When you see this smaller size of your disk, make sure you are looking at the whole disk and just a partition of it. If the disk has been broken into several partitions then of course each will appear smaller than the disk itself. To check the size of the physical disk as detected by the system, use the BIOS setup program or a disk utility like FDISK.
  • Check in your BIOS setup program for a hard disk setting like "Translation Mode". You are looking for a setting that you can set to something like "LBA", "Large" or "ECHS". These are BIOS translation modes. If you cannot find any setting like this, the chances are that your motherboard does not support BIOS translation. If the BIOS date is from July 1994 or later, it should have translation support for large hard disks built into your BIOS, but older ones usually do not.
  • If your motherboard has translation support, make sure it is turned on. Most motherboards automatically enable translation when they detect a larger hard disk, but some BIOSes do not do this properly. It is also possible that if you put a newer disk in place of an old one, that the old standard mode is still set in the BIOS. You will usually want a disk larger than 504 MB to be in "LBA" mode, since this is the de facto standard translation mode for large disks.
  • If you do not have native translation support, you will have to add it to the system in order to allow full access to the disk. There are several ways to do this, generally involving either an upgrade to the BIOS or hardware, or the use of a software drive overlay. This section of the Reference Guide discusses adding translation support to a system..

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