jt -
Sorry for the delay. I've been rebooting repeatedly playing with BIOS and init options for exactly what you are talking about.
Remember: all this worked at 42-47MB/sec w/o any doings on my part under 2.4.
The following has apparently been in dmesg forever (I have no idea about under 2.4):
> ide: Assuming 33MHz system bus speed for PIO modes; override with idebus=xx
So, I tried idebus=100 (My mobo is UDMA/133, but the drive is only UDMA/100).
That gave me a screaming "INVALID PARAMETER" (I think) error. Very close to that. So, I tried idebus=66 and it gave me (in dmesg) an "IMPOSSIBLE PCI SPEED (66000), 33MHz assumed instead." It was also giving me a "use ide0=ata66 to indicate an 80-pin cable" (again, wording may not be exact, but it's close and meaning s/be preserved). "ide0=ata100" also syntaxes, but I did get "ide0=ata66" accepted w/no err msgs. I also noticed the following (again, in dmesg):
> ide0: BM-DMA at 0xfc00-0xfc07, BIOS settings: hda

MA, hdb

io
> ide1: BM-DMA at 0xfc08-0xfc0f, BIOS settings: hdc

MA, hdd

MA
I did *everything* I could think of in BIOS to get hdb seen as either not present, or DMA, thinking that the 1st msg above meant hdb was limiting the channel to 33MHz, but to no avail. It's currently set as UDMA/100 and disabled, but you can see the results below.
Below is a dmesg dump of all I thought might be needed; trying not to overload here! I tried to include nearby 'markers' so you'd know where in the log they are. If I need to be more specific, just let me know.
Early in boot:
>>
Building zonelist for node : 0
Kernel command line: root=/dev/hda5 quiet devfs=mount ide0=ata66
ide_setup: ide0=ata66
Initializing CPU#0
<<
Then, later in boot:
>>
Floppy drive(s): fd0 is 1.44M
FDC 0 is a post-1991 82077
via-rhine.c:v1.10-LK1.1.19-2.5 July-12-2003 Written by Donald Becker
http://www.scyld.com/network/via-rhine.html
eth0: VIA VT6102 Rhine-II at 0xdfffff00, 00:50:ba:2b:46:6a, IRQ 18.
eth0: MII PHY found at address 8, status 0x782d advertising 05e1 Link 45e1.
Uniform Multi-Platform E-IDE driver Revision: 7.00alpha2
ide: Assuming 33MHz system bus speed for PIO modes; override with idebus=xx
VP_IDE: IDE controller at PCI slot 0000:00:11.1
ACPI: No IRQ known for interrupt pin A of device 0000:00:11.1 - using IRQ 255
VP_IDE: chipset revision 6
VP_IDE: not 100% native mode: will probe irqs later
VP_IDE: VIA vt8235 (rev 00) IDE UDMA133 controller on pci0000:00:11.1
ide0: BM-DMA at 0xfc00-0xfc07, BIOS settings: hda

MA, hdb

io
ide1: BM-DMA at 0xfc08-0xfc0f, BIOS settings: hdc

MA, hdd

MA
hda: WDC WD1200JB-00DUA3, ATA DISK drive
ide0 at 0x1f0-0x1f7,0x3f6 on irq 14
hdc: Compaq DVD-ROM SD-M1612, ATAPI CD/DVD-ROM drive
hdd: SONY CD-RW CRX175A, ATAPI CD/DVD-ROM drive
ide1 at 0x170-0x177,0x376 on irq 15
hda: max request size: 1024KiB
hda: 234441648 sectors (120034 MB) w/8192KiB Cache, CHS=16383/255/63, UDMA(100)
/dev/ide/host0/bus0/target0/lun0: p1 p2 p3 p4 < p5 p6 p7 p8 p9 p10 p11 p12 p13 p14 >
hdc: ATAPI 48X DVD-ROM drive, 512kB Cache, UDMA(33)
Uniform CD-ROM driver Revision: 3.12
hdd: ATAPI 40X CD-ROM CD-R/RW drive, 2048kB Cache, DMA
<<
It seems to be reporting everything accurately (drive and controller modes). BTW During the tests I was doing a few minutes ago, all right after a fresh boot, I was getting 33.58-33.80 MHz every time. It looks real suspect....
TIA!
Blue Skies...K