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5.25" IDE HDD for a Pentium 1 build

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First post, by ArrayON_56

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Hello everyone,

I recently got a nice retro Penium 1 build and I’m now exploring it a bit. I’d like to add a 5.25" IDE hard drive to run MS-DOS 6.22, but I’m new to the AT-era (my knowledge is mostly ATX-era), so I’d like some advice before I buy anything.

**The system:**
- Pentium-S 133 MHz
- 32 MB RAM (4 sticks)
- Sound Blaster 16-type card
- Ethernet PCI card
- USB 1.1 PCI card
- Case label: “GST-PENTIUM”
- Chipset: Intel 82430I (ver. B3)
- Motherboard manufacturer or model is unclear

Unfortunately, I haven’t found a manual for this board, so some details are unclear.

I've found some drives from which I'm considering to take one:
- 6.4 GB: https://www.ebay.com/itm/187441992862
- 2.5 GB: https://www.ebay.com/itm/326078424727
- 330 MB Seagate: https://www.ebay.com/itm/177112838558
but my pick is not limited to those.

But the 1+ GB drives are beyond the CHS limit.
Could this cause issues with legacy DOS games/apps, or does most of DOS software support LBA fully?
If the second is the case case, the bigger the better for me 😀

Also, the BIOS seems picky about HDD support.
All my drives give `Disk I/O error` or `Disk read error`, except a 40 GB Seagate 2.5" (via adapter) that actually worked and booted Win98.
Those other drives work in other PCs, so it must be some limitation of this PC/BIOS, thus I'm afraid that even not all older 5.25" drives would work.
Also, what I noticed mainly on the 3.5" IDE HDDs, that the bios would automatically detect them as 8GB, which is incorrect, and would not recognize them even after setting the geometry manually according to values written on HDDs label.
So could the limit be 8GB for drives for problem-free operation?
(For 2.5" ones, mainly the 40GB Seagate that worked I cannot tell rn, because I accidentally broke the adapter and I'm waiting for new ones to arrive, so I'll check and post then if it is relevant. )

Is there anything else I should watch out for when picking such drive for this pc?

Any tips or gotchas before I pull the trigger on one of these drives would be greatly appreciated!
Thanks in advance.

PS: If some needed info is missing, please let me know and I will check/post it 😀

Reply 1 of 5, by jakethompson1

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LBA translation isn't an issue for DOS software, with some exceptions like 32-bit disk access.

The maximum translated CHS geometry that can be accessed via DOS and Win95a via Int 13h is 1024/255/63 which is 8.4GB. To go beyond that, a new interface had to be standardized (Int 13h Extensions), and your BIOS doesn't have it.

The good news is, on my own Pentium systems with Award BIOS of that era, you can either use an enormous drive (1TB SATA HDD with SATA-IDE converter even on one system of mine) and just use it as 8.4GB, leaving the rest of the space inaccessible, or install overlay software like EZDrive or OnTrack to access the rest.

You can also look for and install a BIOS update. But some Award BIOSes have a bug where they lock up if the disk is over 32GB, you can't just ignore the rest of the space. Yours is so old it's immune to that bug but has the 8.4GB limit.

Are you sure a 5.25" HDD will physically fit?

Reply 2 of 5, by wbahnassi

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What about Seatools? Can't it be used to shrink the drive to the CHS limits and make the BIOS happy? This way any HDD from last decade can be used, and these are dirt cheap if not free in local market places...

Turbo XT 12MHz, 8-bit VGA, Dual 360K drives
Intel 386 DX-33, Speedstar 24X, SB 1.5, 1x CD
Intel 486 DX2-66, CL5428 VLB, SBPro 2, 2x CD
Intel Pentium 90, Matrox Millenium 2, SB16, 4x CD
HP Z400, Xeon 3.46GHz, YMF-744, Voodoo3, RTX2080Ti

Reply 3 of 5, by ArrayON_56

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Yup, under the external 5.25" position where the big FDD is, is one internal 5.25" position, where I could add the drive.

Limiting space of such drive feels like wasting the drive, but could be good for testing ig. How is it being done? Must the drive support it through some jumper configuration?
I plan to install overlay software, but I do need to install it on disk that the bios can properly detect and read from, thus enabling access to other, bigger drives, right?

Updated BIOS seems like the best option if it could overcome the hdd addressing limits, ideally without the >32GB bug, but first I need to get more info about the board, which i believe will be doable using some sw as hwinfo, thus I need to make this thing boot anyhow.

PS: The SeaTools sounds interesting too, I will look at it.

Reply 5 of 5, by chinny22

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Re the hard drives not been detected properly, my FIC PPro board had similar issues using an 80pin IDE cable.
Swapped this for a 40Pin cable and immediately not only were hard drives were detected correctly, but read/write errors disappeared.
Maybe worth a try?

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