ZERO.

The cache is to help slow drives, that get a lot of constant writes/reads.

The cache is normally used as a buffer. If you write 10mb to the disk, it happens "instantly", while the controller writes to the disk at 1mb/s (exaggerated) And then its all done. So if you immediately read from that drive, it still pulls from the drive at 1mb/s (again exaggeration)

So if your use case are large chunky writes to a slow drive, it will be helpful. otherwise its total dickwaving. (I fully support this use case) SCSI raid caches are not much different, but are a bit smarter, and subsequently much more expensive.

luckybob, where do you get your information?

Cache's most significant improvement comes in the form of latency. Everything is way faster with cache than without it. Uncached HDD is snail-slow. The difference is similar in nature as HDD vs SSD in modern computers.

Though, there are things like smartdrive, that do caching into RAM and don't require special IDE controller.

real world experience.

the cache is too "dumb" from this era. It is basically a hardware version of the smartdrive you mentioned. Cache today will easily store commonly used data, this cache is little more than a buffer.

and don't forget cache sits on a card that is connected via ISA bus. That's the limiting factor by itself. I'm yet to test my Promise ISA cache controller 🤣

My real life experience has been very opposite. With smart drive for example, the latency of ram is just so much smaller than hdd, that you feel you did a full generational upgrade to the whole box. Old computers don't need that much bandwidth, but latency is very important.

"Cache is little more than a buffer", is it? Then how? What about CPU caches?
Usually, hard drive cache is block level buffer in order over access time, so the oldest block can be purged if cache is full.

Maybe your cache setups have never worked right, luckybob?

I’m curious about SimonV’s computer specs and usage. 16mb seems like a huge amount of cache for the time. I would think many programs would fit entirely in cache and see very fast load times on repeat usage.

If using an old/slow HDD, then yeah, you will notice a difference. Maybe not so much if you are using Smartdrv.

If you put an SSD on a regular IDE controller, then it will be faster than a HDD with a caching controller

It's a bridgeboard in an A3000T. It's a 386sx 25mhz upgraded to a 50mhz 486slc makeit486 and a 387 fpu. Well the cache controller has 4x4mb 30pin simm on it because * I can * and 4gb DOM on it. So it's VERY fast imho. I guess I will know soon enough how fast or slow it is compared to a normal ide controller. That is if I get that DOM working on it with EZdrive ... struggling with that for the moment.

All caching controllers have their own CPU to handle transfers and cache so at the very least on a 286 to early 486 ISA only system you are getting the benefits of low main CPU ultilization (like newer systems with DMA) plus saving the onboard RAM that would normally be used by smartdrive for app use. On old slow systems it makes a difference.

I've got a 486DX2/50 system with ISA cached hdd controller. It was used as wfw 3.11 file server on a network.