Marco wrote on 2024-04-02, 11:03:Thanks. I assume we both used hdds / CFs
With muuuuch more capabilties than any PIO mode. […]
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Thanks. I assume we both used hdds / CFs
With muuuuch more capabilties than any PIO mode.
One add-on: according to this page:
https://forum.vcfed.org/index.php?threads/isa … fer-rate.57260/
The cpu speed will make a difference as higher clock speeds will reduce I/O cycle times of the CPU needed for any file transfer (if understood correctly).
I also wonder whether the there mentioned chuck mod can make a difference on our 386 systems as well.
Most CF's do declare that they support block transfer mode, but their max block transfer size is almost always fixed = 1.
Most HDD's > 1995 support block transfer mode and frequently have a max block transfer size of 16 or larger.
My understanding is that it works some thing like this:
- CF with block size = 1: Send Read Command for 512 bytes - Wait for CF to process command - Wait for CF to say data is ready - Read 512 bytes from buffer - Repeat 15 more times
- HDD with block size = 16: Send Read Command for 8 KB- Wait for HDD to process command - Wait for HDD to say first sector is ready - Stream 8 KB from buffer
So the CF has 15x overhead of ATA commands, IRQ's, and Buffer reads, stealing away a lot of ISA cycles. There's probably some latency introduced between each request as well, waiting for the tiny processor in the CF to prep each requests "ala carte" instead of "assembly line". A fast CF's can pull ahead of just about any mechanical HDD in the linear read test, but they need a bus speed that is much higher than the HDD max read speed in order to hide the overhead.
I've seen CPU clock speed have a measurable effect on raw disk transfers with VLB controllers. The higher the CPU clock speed, the faster the transfer rate, with a 133Mhz 486 doing better than a Pentium overdrive. It wasn't large but it was there. I haven't played around with ISA buses faster than 10Mhz, so I'm not sure how much the CPU is going to affect things there.
There are other places where CPU speed can come into play besides raw throughput, such as file system processing, CHS translation, smart drive, etc.