Date   : Tue, 26 May 1998 13:10:26 BST
From   : Chris Thornley <osu036@...>
Subject: Re: High density

Hi,
Do you have details of the ST upgrade as HENSA has removed its ST files?
Also what where the part numbers of the other two chips mentioned (WD / Intel)
and where could I obtain there 
datasheets?

I posted a reply to one message on the WD chip but it seems to have not been
displayed.

.....(This is simlilar to what was not posted)
       Theoretically any 8bit disc controller chip can be used what has to be taken
it to account is whether 
the bbc can handle the 500kbits/s data rate for HD drives. LD drives operate
at 250kbits/s and FM drives will 
operate at a lower rate. The 1Mbit/s speed is for the not so popular 2.88MB
3.5inch drives. If the bbc can not 
operate at the 500kbits/s speed theres another option. Half the motor speed
of the drive and write at 250kbit/s. 
I belive commadore and a few amiga compaines sell these half speed internal
drives which can be used.  

       Another major problem with now chips is registers. i.e when the bbc changed
from i8271 to WD17xx 
seris of controllers there registers where different and not all the instruction
of the older intel chip could be 
emulated on the WD controller. This was a major problem for some games and
software which relied on copy 
protection. Some later DFS`s emulated some these registers and software calls
and provide a resonable form 
of compatablity but could not emulate all the functions. Also software which
directly writes to the hardware (for 
speed increase or other) is going to fail unless some cleaver way of interception
if found or more than one 
chip can be fitted.

       Also there is the page issume to consider when writing a new filesytem,
Page is the aproximate size 
of exactly one whole track on a DNFS if it set around &1900 and changes when
you start to muck around with 
muliple catalogues and diferent disc geometry. This problem can be solved
in certain circumstances by using 
shadow ram boards or using code which copies this info in sideways ram. But
there still may be an 
incompability problem relating to page.

       The only companiey I am awre of that produced HD discs for the bbc where
solidisk. This product for 
some reason did not get reviewed in BBC microuser but it might of done in
A&B computing which I have not 
got many issue off. The solidisk unit I think required you to already own
a certain disc controller. Came with 
two (teac?) floppy drives and a STLHDFS rom which I think some how patched
ADFS and DFS roms to work 
with the system. I think there was a modification sheet which probally played
around with the jumpers to do 
with 8 inch drives.

       Another either im thinking of concerns the OPUS challenger drive system.
How was this impilmented 
so it could work of the 1Mhz but and it could work with standard DFS ADFS
etc. Does anyone have a schematic 
of the OPUS challeger with the ram board? And even a way of generating source
code from the challeger 
roms?

Thanks 
Chris

On Sun, 24 May 1998 19:04:24 +0100 Dave wrote:

> From: Dave <dfl@...>
> Date: Sun, 24 May 1998 19:04:24 +0100
> Subject: RE: [BBC-Micro] High density
> To: bbc-micro@...
> Cc: bbc-micro@...
> 
> In message <000401bd86e2$a6920440$0100a8c0@...>
>           "Mark Usher" <marku@...> wrote:
> 
> > Hi Chris
> > 
> > > hardware refernce manual. A similar sort of speed modification
> > > people have done on Atari ST who use
> > > WD1773 chip which is esentailly the same and TRS80s which either
> > > uses wd1773 or the older version of the
> > > chip. I`ll see if i can find the ST modification details on HENSA.
> > I did the 1.44MB floppy upgrade for a friend about 2 years ago. I have lying
> > around a WD1772 which I removed from the STE. This was the standard DD FDC
> > fitted to the ST range. I wish I could  remember what I fitted in it's
> > place. I'll have to hunt about a bit. I have the info somewhere.

               />      Christopher J. Thornley is OSU036@...
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