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CF-IDE disk size wrongly recongized in dos

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First post, by lijiaxuan

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I have two vintage Compaq Contura 400CX laptops and successfully made a working one out of them. I also put a 2-gig CF flash card in place of the original HDD. After partitioning, formatting and installing the OS (MS-DOS 5.0), things seemed to work normally. However, I discovered the partition is only 512 megabytes in size. I then re-partitioned it with Windows 98 boot floppy and found its size is still 512 megs. I switched a 4-gig CF on, everything still stayed the same. I am pretty confused, as I have heard that FAT 16 supports 2 gigs per partition. What could be the reason of the size shrink? Thanks!

Reply 2 of 7, by lijiaxuan

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Disruptor wrote on 2024-04-29, 12:45:

You ran into the CHS (cylinder, head, sector) limit of 1023 x 16 x 63.
What size had your original HDD?

Well, the drive is removed before I got the laptops, but I assumed they were 250 megs in size. I also found that the BIOS have already correctly recognized the CF card as 2000 megs. I still don't know why it doesn't work.😢

Reply 3 of 7, by Disruptor

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Well, that depends on how the BIOS is telling the operation system the CHS translation.
While some earlier BIOSes continue the cylinder number above 1024, others increase the cylinders to 255 (to get up to 8 GB).
However, DOS cannot deal with more than 1023 cylinders.
Perhaps your BIOS supports something like disk mode (AUTO, Normal, Large, LBA). LBA is preferred.

And about which DOS version are we talking about?

Reply 4 of 7, by lijiaxuan

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Disruptor wrote on 2024-04-29, 13:23:
Well, that depends on how the BIOS is telling the operation system the CHS translation. While some earlier BIOSes continue the c […]
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Well, that depends on how the BIOS is telling the operation system the CHS translation.
While some earlier BIOSes continue the cylinder number above 1024, others increase the cylinders to 255 (to get up to 8 GB).
However, DOS cannot deal with more than 1023 cylinders.
Perhaps your BIOS supports something like disk mode (AUTO, Normal, Large, LBA). LBA is preferred.

And about which DOS version are we talking about?

Emm, I am using DOS 7.1 right now. I know it is not a offical version, but it still worked quite fine from me previous experience. It also supports FAT 32 but it still recognizes the drive total size as 512 megs anyway.

Reply 7 of 7, by douglar

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lijiaxuan wrote on 2024-04-29, 14:31:
Disruptor wrote on 2024-04-29, 14:20:

Perhaps you need a DDO.
An example is Ontrack Disk Manager.

Ok, thanks. I'll try.😄

We have a collection of them here: http://vogonsdrivers.com/index.php?catid=19

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