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04.08. Can large drives be used with my old BIOS?




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This item is from the Yet Another Enhanced IDE/Fast-ATA/ATA-2 FAQ, by John Wehman and Peter den Haan with numerous contributions by others. (v1.92).

04.08. Can large drives be used with my old BIOS?

Yes, in principle, but there's still the small matter of the 504MB barrier. If the new drive exceeds this capacity, you must have an Enhanced BIOS in order to use more than 504MB with DOS, Windows or Win95 (see Q4.10 for other operating systems). It is important to note that this is a software only issue: you do not need a special interface to support large drives.

BE WARNED that some older BIOSes will incorrectly handle drives with more than 1024 cylinders. Instead of truncating the number of cylinders to 1024, they use the cylinder count modulo 1024, which means that a 2300 cylinder drive will appear to have just 252 cylinders. The solution is to specify 1024 cylinders in the BIOS setup.

This becomes a real problem when a BIOS with this error also won't allow you to enter the drive parameters manually. Among IBM systems, the 1991-vintage PS/2 models 35sx and 40sx, the ValuePoint I, and at least some of the ValuePoint Si models have this flaw. With these machines, you should either try go get a BIOS upgrade from <ftp://ftp.pcco.ibm.com> if you have a flash BIOS, or verify that the drive you intend to use has a way to fake having no more than 1024 cylinders (Western Digital has a utility for their 540MB drive, and many Maxtor drives have a jumper). The Promise EIDEMax is also reported to work, and will allow you to use drives of up to 8GB in full. Note that some operating systems, such as Linux and OS/2, allow you to override the BIOS' drive geometry information, which may also help addressing this problem. Another option is using OnTrack Disk Manager version 7.

 

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next page: 04.09.  I need an Enhanced BIOS to access >504MB. How do I get one?