Posted By
gerliczer
on 2020-04-28
02:25:56
|  Re: Overclocking PAL 264s
OK, MMS. Let's do some sort of "on back of a napkin" calculation:
The nominal rotational speed of a 1541/1551 is 300 RPM. That means 0.2 sec for each revolution. Reading one sector (meaning 256 useful bytes for the calculation) needs, depending on which track holds it, ~9500..~11500 micro-secs (overestimated). Let's assume 10000.
Somewhere I read that transferring one byte in 1541 IEC protocol takes 800 micro-secs (net time). Therefore transferring 256 bytes equals 204800 micro-secs. Altogether 214800.
Let's assume that TCBM protocol accelerates transmission to 8x of IEC. That means 25600 micro-secs. Add the 10000 of sector read and the total will be 35600.
214800/35600 is around 6.
What we omitted from the calculation are:
- sector read delay (up to about 180000 micro-secs - well, hello gorgeous)
- GCR decoding time (AFAIK, 1551 does that at about twice the speed of 1541)
- and transfer setup, synchronisation and administration overhead.
Still not impressed?
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