It depends on the motherboard BIOS. Some of the later ones are good up to 8GB+.

If you get a PCI SATA 1 RAID card, you can go up to whatever as the card's BIOS handles it.

A workaround is to use a drive overlay software.

Using XT-IDE bios gets around this as well. You can fit it in a nic boot rom socket or use a dedicated XT-IDE card like I have done on my XT Turbo system.

cyclone3d wrote on 2021-05-10, 19:51:

It depends on the motherboard BIOS. Some of the later ones are good up to 8GB+.

If you get a PCI SATA 1 RAID card, you can go up to whatever as the card's BIOS handles it.

A workaround is to use a drive overlay software.

i got an almost new soyo sy-4saw2 which in the manual it states the jumper setting for amd x5, i think its one of the last cpus ever made for 486, therefore i thought the motherboard was late era 486s.
and when i tried to format an sd card i got a 1GB limit.

its not like the 32gb bios limit patch right? these old bios can´t be patched?

Trying to make even more clear what cyclone3d already wrote: there is no CPU/486 limitation, max size is not dependent on the CPU so there is no correct number "for a 486".
It's a BIOS limitation so during the era of 486 CPUs the limit varied from the classic 500-something MB to the rare 4GB or the even rarer 8GB.

Here's what I typed up:

IDE and BIOS Limits & Incompatibilities

• 528 MB limit - BIOS before July 1994 rarely support drives over 528MB. They were limited to Cylinders <= 1024, Heads <= 16, Sectors/Track <= 63
• 2015 MB limit - BIOS before May 1996 rarely support drives larger than 2015 MB. They were limited to Cylinders <= 4095, Heads <= 16, Sectors/Track <= 63
• 3277 MB limit - Phoenix BIOS 4.03 and 4.04 config screens lock when a drive is configured with a capacity over 3277 MB.
• 4.2 GB limit - Some BIOS before February 1997 have the first ECHS (Extended CHS) limit. DOS and Windows 95/98 cannot handle 256 heads. 'Large' mode in the BIOS produces an alternate geometry by doubling the number of heads and halving the number of cylinders shown to DOS until cylinders <= 1024. The limit for this method is 4032 MB (C=1024, H = 128, S = 63) for drives that report 16 heads.
• 7.9 GB limit - Other BIOS from this period had a Revised ECHS limit. 'Large' mode in the BIOS presents an alternate geometry using multiples of 15 heads, up to 240 heads. This method stops working at 7560 MB (C=1024, H=240, S=63)
• 8.4 GB limit - Final ECHS limit - Bios geometry selects head head value from the sequence 16, 32, 64, 128, 255 to present an alternate geometry up to (C=1024, H=255, S=63). Hard drives larger than 8.4GB report a geometry of C=16383,H=16,S=63 to indicate that they are larger than can be described using ECHS geometry translation)
• 33.8 GB limit - BIOS before August 1999 often stored the cylinders as a 16 bit value, so they could not process cylinders > 65535.
• 137.4 GB limit - BIOS before September 2001 only used ATA-5, which used 28 bits to identify each LBA sector, limiting drive capacity to 137GB. ATA-6 added an additional 48bit LBA sector field. Hard drives over 137.4 GB should report an LBA capacity of 0xfffffff sectors and report the actual value in the 48-bit field.
• Early LBA drives do not always work correctly with mature LBA controllers and may need to be manually configured to use 'CHS' mode for correct operation.
• Some contemporary storage devices exhibit compatibility issues negotiating a compatible protocol with some early ATA-3, ATA-4 controllers and do not function. Issue appears to be more common with UDMA6 devices like Sinitechi SD adapters and Hyperdisk DOM devices than devices limited to UDMA5 such as the Leidisk DOM or smaller capacity CF cards.

douglar wrote on 2021-05-10, 23:35:

Here's what I typed up: […]
Show full quote

Here's what I typed up:

IDE and BIOS Limits & Incompatibilities

• 528 MB limit - BIOS before July 1994 rarely support drives over 528MB. They were limited to Cylinders <= 1024, Heads <= 16, Sectors/Track <= 63
• 2015 MB limit - BIOS before May 1996 rarely support drives larger than 2015 MB. They were limited to Cylinders <= 4095, Heads <= 16, Sectors/Track <= 63
• 3277 MB limit - Phoenix BIOS 4.03 and 4.04 config screens lock when a drive is configured with a capacity over 3277 MB.
• 4.2 GB limit - Some BIOS before February 1997 have the first ECHS (Extended CHS) limit. DOS and Windows 95/98 cannot handle 256 heads. 'Large' mode in the BIOS produces an alternate geometry by doubling the number of heads and halving the number of cylinders shown to DOS until cylinders <= 1024. The limit for this method is 4032 MB (C=1024, H = 128, S = 63) for drives that report 16 heads.
• 7.9 GB limit - Other BIOS from this period had a Revised ECHS limit. 'Large' mode in the BIOS presents an alternate geometry using multiples of 15 heads, up to 240 heads. This method stops working at 7560 MB (C=1024, H=240, S=63)
• 8.4 GB limit - Final ECHS limit - Bios geometry selects head head value from the sequence 16, 32, 64, 128, 255 to present an alternate geometry up to (C=1024, H=255, S=63). Hard drives larger than 8.4GB report a geometry of C=16383,H=16,S=63 to indicate that they are larger than can be described using ECHS geometry translation)
• 33.8 GB limit - BIOS before August 1999 often stored the cylinders as a 16 bit value, so they could not process cylinders > 65535.
• 137.4 GB limit - BIOS before September 2001 only used ATA-5, which used 28 bits to identify each LBA sector, limiting drive capacity to 137GB. ATA-6 added an additional 48bit LBA sector field. Hard drives over 137.4 GB should report an LBA capacity of 0xfffffff sectors and report the actual value in the 48-bit field.
• Early LBA drives do not always work correctly with mature LBA controllers and may need to be manually configured to use 'CHS' mode for correct operation.
• Some contemporary storage devices exhibit compatibility issues negotiating a compatible protocol with some early ATA-3, ATA-4 controllers and do not function. Issue appears to be more common with UDMA6 devices like Sinitechi SD adapters and Hyperdisk DOM devices than devices limited to UDMA5 such as the Leidisk DOM or smaller capacity CF cards.

That's a nice and very focussed summary. Awesome! 👍

konc wrote on 2021-05-10, 20:47:

Trying to make even more clear what cyclone3d already wrote: there is no CPU/486 limitation, max size is not dependent on the CPU so there is no correct number "for a 486".
It's a BIOS limitation so during the era of 486 CPUs the limit varied from the classic 500-something MB to the rare 4GB or the even rarer 8GB.

4gig to 8gig ide BigFoots were as common as cow poo. I've still got 6 serviceable ones. I have a 4gig one running in my XT Turbo system.

Caluser2000 wrote on 2021-05-11, 06:22:

konc wrote on 2021-05-10, 20:47:

Trying to make even more clear what cyclone3d already wrote: there is no CPU/486 limitation, max size is not dependent on the CPU so there is no correct number "for a 486".
It's a BIOS limitation so during the era of 486 CPUs the limit varied from the classic 500-something MB to the rare 4GB or the even rarer 8GB.

4gig to 8gig ide BigFoots were as common as cow poo. I've still got 6 serviceable ones. I have a 4gig one running in my XT Turbo system.

Pretty sure that BIOS support of 4GB and 8GB support was rare on 486 machines.. not the drives themselves.

Thats why Enhanced IDE controller cards were produced by Promise and others.

More info on the drive overlay software cyclone3d mentioned
https://youtu.be/3Z15jdZEJiY
https://youtu.be/8LzCB6kDVC8

XT-IDE is done in hardware but requires either ability to program the chip or purchase something ready made This video gives a brief summary of the whole HDD limit issue and what XT-IDE does
https://youtu.be/pCdQ6MWnNpU

Or you can bypass the onboard IDE completely with a addon card.

Personally I'd try overlay first as its completely free. I noticed no performance loss on my 486.
XT-IDE is "cleaner" as its done on hardware level (well as much as BIOS is hardware) but doesn't seem to actually make a difference, at least on 486's

Caluser2000 wrote on 2021-05-11, 08:10:

Thats why Enhanced IDE controller cards were produced by Promise and others.

Anyone have a bios image for a Promise EIDEMAX, EIDEMAX II, EIDEPRO, or DriveMAX card that supports LBA?

https://web.archive.org/web/19970416030210/ht … ultSupport.html
https://web.archive.org/web/20000829074800/ht … ts/IDEcards.pdf