Disk BIOS Speed

Enlighted (4156)

12-01-2022, 23:13

Someone pointed out that there are two different "kind or famlily" of Disk Bios implementations for 3.5" floppy disks.
One is faster than the other and this is due to the manufacturer.
Anyone knows about the difference in speed? (i think is mainly transfer rate speed),
what is the factor between the two?
it is due to the fact that (i've heard about, not sure) one is I/O based and the other is memory mapped?
Or it's mainly a different hw that is the reason of speed difference?

I've got an NMS8245 stock. Does the internal drive falls into the category "slow" or "fast"?
thx in advance.

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Par zeilemaker54

Champion (355)

13-01-2022, 08:16

In general, there are quite a lot of different drivers (but only 2 major FDC families, WD x79x and NEC 765).
In terms of speed:
Some have slower seek (mostly older), most use fastest seek
Some have faster page 0 transfers (not using a routine in $SECBUF)
Most have FDC mirroring (when memory mapped based), allowing somewhat faster page0/page1 transfers
Some have interrupts disabled longer
Some have shorter motor spinup wait time
Some have shorter head settle wait time
Some have implemented hardware disk change instead of software
Some have implemented hardware motor stop timer
Some have timer interrupt handler, few have not

There is no speed difference between I/O based and memory based FDC
And I would say that there is also no difference between internal and external FDDs, but there could be differences between the actual drives being used in terms of head settle and motor spinup.

Par PingPong

Enlighted (4156)

13-01-2022, 11:21

thx, i've heard about two different categories, but i do not recall precisely, maybe the issue was between Philips vs Sony FDC implementations?

Par zeilemaker54

Champion (355)

13-01-2022, 12:18

PingPong wrote:

thx, i've heard about two different categories, but i do not recall precisely, maybe the issue was between Philips vs Sony FDC implementations?

The Sony HB-F500/F700 driver is an example of the slow seek. But the hardware (FDD) accepts fastest seek without any problem. That is why there are replacements ROMs for the Sony.
In fact, the Sony hardware has features which are only parly being used. It has hardware support for disk change and the hardware FDD motor off timer could be used more efficient.