As questioned in the subject: What optimization is done in a fask disk rom to make it faster ?

Generally the code in the diskdriver optimized to execute faster. A common way to speed up execution is to disable the interrupts during disk i/o. Also with the WD2793 controller, a common way to speed up disk i/o is to use the fastest track seek speed (programmable wit the WD2793). Original SONY diskrom's for example do not use the fastest speed possible, and are therefore slower than a PHILIPS diskrom, alltough they are both using the same hardware.....