Hard disk 467GB limit in 9x/ME DOS?

[SomeGuy]

Just for the heck of it, I have been trying to put Windows 9x on a 1 Terabyte SATA hard drive.

However, when I try to partition it or do anything in DOS mode, the drive appears as only around 450 Gigabytes. Anything beyond that appears to be unreadable by DOS. Once Windows is loaded with the drivers it can see the rest of the drive. Windows NT/Linux can also see the entire 1Tb drive without problem.

For example I can create one large 467 gigabyte partition with 900684162 sectors from DOS that is fully accessible. (Never mind there are potential data corruption issues with that), then from Linux fill the rest of the drive with a ~500 gig extended FAT32 partition that should be DOS drive "D". Real mode DOS will refuse to see that drive, but when Windows 9x loads with the SATA driver the drive is suddenly visible and accessible.

I have tried this with a Windows 95 OSR/2 (with Fdisk update), Windows 98SE, and Windows ME boot floppy, all with the same result.

Currently, it looks like either a limitation in Win9x DOS or the SATA card's bios. I'm using a VT6421A based SATA controller card, and the drivers actually work great with Windows 95, 98, and ME. The BIOS in my 6421 SATA RAID card might be a little old, but as far as I can tell it is not possible to flash update it.

Over the years I have seen many, many, drive limits but I am not familiar with this one. I am curious as to what specifically the issue is here, I figure if anyone would know it would be someone here (And Google is turning up zilch). On the compatible hardware topic I do see a general reference stating "DOS, WINDOWS and SCANDISK (in DOS Mode) can handle at least 400GB", is this talking about the same limit I'm running in to here?

Thanks.

[rloew]

Just for the heck of it, I have been trying to put Windows 9x on a 1 Terabyte SATA hard drive.

However, when I try to partition it or do anything in DOS mode, the drive appears as only around 450 Gigabytes. Anything beyond that appears to be unreadable by DOS. Once Windows is loaded with the drivers it can see the rest of the drive. Windows NT/Linux can also see the entire 1Tb drive without problem.

For example I can create one large 467 gigabyte partition with 900684162 sectors from DOS that is fully accessible. (Never mind there are potential data corruption issues with that), then from Linux fill the rest of the drive with a ~500 gig extended FAT32 partition that should be DOS drive "D". Real mode DOS will refuse to see that drive, but when Windows 9x loads with the SATA driver the drive is suddenly visible and accessible.

I have tried this with a Windows 95 OSR/2 (with Fdisk update), Windows 98SE, and Windows ME boot floppy, all with the same result.

Currently, it looks like either a limitation in Win9x DOS or the SATA card's bios. I'm using a VT6421A based SATA controller card, and the drivers actually work great with Windows 95, 98, and ME. The BIOS in my 6421 SATA RAID card might be a little old, but as far as I can tell it is not possible to flash update it.

Over the years I have seen many, many, drive limits but I am not familiar with this one. I am curious as to what specifically the issue is here, I figure if anyone would know it would be someone here (And Google is turning up zilch). On the compatible hardware topic I do see a general reference stating "DOS, WINDOWS and SCANDISK (in DOS Mode) can handle at least 400GB", is this talking about the same limit I'm running in to here?

Thanks.

DOS 7 is not limited to 500GB. I have used it up to 2Tb without problems. With larger sectors, I have created a 64TiB Partition.

The main limitation is FDISK, which cannot handle more than 512GiB. Some older SATA BIOSes topped out at 512Gib, but then the Computer would not even boot if the limit was exceeded.

[Guest wsxedcrfv]

Just for the heck of it, I have been trying to put Windows 9x on a 1 Terabyte SATA hard drive. However, when I try to partition it or do anything in DOS mode, the drive appears as only around 450 Gigabytes.

See this thread:

[SomeGuy]

After doing some more research I think I better understand what is happening here. This is indeed the 512 gigabyte limit. I got thrown off because I did not expect the size value to wrap around and I did not expect some other (obviously obsolete) disk utilities of mine to behave in the exact same way. Also that drive not appearing problem was a separate issue due to another buggy partitioning program I tried. Once partitioned properly DOS can indeed access the entire drive.

From what I have read, the problem is that some programs translate LBA back in to CHS using 255 heads, 63 sectors per cylinder and a maximum of 65535 cylinder.

65535 * 255 * 63 = 1052819775 sectors or 512 Gigabytes.

Using this method my drive of 1953525120 LBA sectors would come out as, i think, 121601 cylinders which would overflow and wrap around to 56066 (which is, in fact what is reported by one of my obsolete disk utilities) resulting in the apparent 467 gigabyte size.

So after going through several partition programs I settled on using the Ubuntu 10.04 partition program from its live CD.

So far DOS can see the entire drive OK and a bunch of partitions I created, but now I am investigating a slightly different problem...

In real mode DOS if I test a FAT32 partition by filling it up with large dummy files, the FAT gets overwritten and corrupted after writing somewhere just over 128 gigs. It doesn't seem to matter where the partition is, I was mainly testing one towards the end of the disk so it shouldn't be a disk LBA issue. The corruption stayed within the partition, it did not corrupt any of the other partitions suggesting it might be a file system issue. I tested this a number of times on different partitions under 9x and ME DOS with the same result. No corruption seems to occur at all when inside Windows. I'll test that some more when I get a chance, it takes a while to fill up the drive.

[dencorso]

Big HDD & 48-bit LBA Thread Index (On using HDDs larger than 137 GB (128 GiB) with Win 9x/ME)

STFF