Don't think there's any way to tell it the ROM is faster.
Most BIOSes only seem to allow you to swap shadow for extended when there is just 1MB installed

Matth79 wrote:

Don't think there's any way to tell it the ROM is faster.
Most BIOSes only seem to allow you to swap shadow for extended when there is just 1MB installed

Why would you need to?

If the ROM is replaced with a faster one, it should, in theory, make it so you don't need to shadow it to RAM, which in turn would give you more RAM to work with.

I would say to go ahead and try it and report the results.

Don't forget the ROM has a slower connection to the system than RAM does. It depends on the motherboard but the RAM usually has a direct connection to the CPU, while the ROM goes over a slower channel like the ISA bus.

If you have a memory expansion card on the ISA bus then it might run at the same speed as a fast ROM chip so you'd get no benefit from shadowing. Also remember that on top of the slower connection, ROM chips usually read one byte per cycle while RAM can read up to eight bytes per cycle depending on architecture (30-pin RAM is also one-byte, but 72-pin is 4-byte and paired 72-pin like in Pentiums is 8-bytes/cycle.)

It's always worth testing, but I think in this case there won't be much of an improvement for most cases, unless you find a particularly unusual motherboard with the ROM wired up differently.

Also keep in mind that BIOS shadowing is only helpful for DOS. If you’re running Windows 9x or greater it’s pointless as hardware access is direct (it bypasses the BIOS all together).

That's a very good point, and most games also access the hardware directly (video, sound, keyboard) and use DOS services for disk access, which is in RAM anyway.

Wrong forum. Ask old hardware questions in Marvin. This forum is for DOS games on modern systems.

Marvin, the Paranoid Android

Malvineous wrote:

Don't forget the ROM has a slower connection to the system than RAM does. It depends on the motherboard but the RAM usually has […]
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Don't forget the ROM has a slower connection to the system than RAM does. It depends on the motherboard but the RAM usually has a direct connection to the CPU, while the ROM goes over a slower channel like the ISA bus.

Thanx for the information, and that's what I was afraid for that the BIOS is connected via a slower way.
But A 386 computer has everything over the ISA bus ? ( Neumann architecture )
Maybe RAM is direct connected the the CPU and the rest over the ISA bus.

If you have a memory expansion card on the ISA bus then it might run at the same speed as a fast ROM chip so you'd get no benefit from shadowing. Also remember that on top of the slower connection, ROM chips usually read one byte per cycle while RAM can read up to eight bytes per cycle depending on architecture (30-pin RAM is also one-byte, but 72-pin is 4-byte and paired 72-pin like in Pentiums is 8-bytes/cycle.)

I see you're completly right.

It's always worth testing, but I think in this case there won't be much of an improvement for most cases, unless you find a particularly unusual motherboard with the ROM wired up differently.

The computer:
Xycom XVME 686
It's a VME bus single board computer 386sx with 1 mb RAM ( 4 and 8 mb versions, this version is 1mb )
An industrial mainboard and you can add Example : ethernet card or RS485 Card all over the VME bus
VME bus is 32 bit
I don't know which chipset architecture this board has.

A computer with ony 1 mb RAM with BIOS shadows enabled = no extended memory left
A computer with ony 1 mb RAM with BIOS shadows disabled = 384 extended memory left

It's only for DOS (Freedos) and music trackers (Inertia Player and Fasttracker)

collector wrote:

Wrong forum. Ask old hardware questions in Marvin. This forum is for DOS games on modern systems.

Marvin, the Paranoid Android

Yes now I see,
General old hardware 😎