Re: "Star Wars" demo?

[dempson@atlantis.actrix.gen.nz (David Empson)]

In article <31AECD9C.41C67EA6@sci.kun.nl>,
Doede Boomsma  <dboomsma@sci.kun.nl> wrote:
> Michael Hickey wrote:
> 
> > It occupied all of a Apple 40SC Hard Drive, and used a patched ProDOS to
> > get over the 32mb partition limit.  As mentioned by Leif, it was put
> > together to demo the new Apple High Speed SCSI Card's  DMA ability and 
> 
> Okay, here we see it again.. Prodos patch for the 32kb limit!

Ah, the old myth rears its head again.

ProDOS-8 has never been patched to support more than 32MB, to my
knowledge.  Doing this is next to impossible, as P8 has a fixed block
size of 512 bytes, and uses a 16-bit block number, which limits you to
65535 * 0.5K = 32767.5KB per disk.

Apple's High-Speed SCSI card DMA demo did not use ProDOS at all
(except for loading the program).  The data was read from the drive
using direct SCSI READ calls (using the SCSI card's looped DMA data
transfer mechanism), via a SmartPort call.  Given a fast enough hard
drive, this method allows transfers at rates up to 1 MB per second on
a IIgs.

The looped data transfer was copying 32K chunks of data straight from
the hard drive into screen memory, then updating the parameter block
for the next read.  It should have been able to achieve 30 frames per
second.
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand