🚀 go-pugleaf

On Tue, 11 Jul 95, Kenwyn M. Smith wrote:

KMS> James Allcock (case@innotts.co.uk) wrote:
KMS> : 
KMS> : Isn't there a problem when you go above a certain amount of
KMS> : memory? I think it's 4Mb? Starts to interfere with your PCMCIA
KMS> : socket.
KMS> : 
KMS> This is a limitation of the 020 CPU, 030's have diferent memory addresses
KMS> and are not subject to this limitation.

Yup.  AFAIR, the 68020 can only actually address 16M of memory (only?!) due to
having only a 24-bit address bus, whereas the higher members of the 680x0
family have the full 32-bit address bus implemented, offering 4Gb addressable
memory (don't get too excited, that'd cost around GBP130,000 to populate at
today's prices :-().

Now, in the 16Mb of the 68020, the Amiga has to fit 2Mb chip plus 8Mb fast RAM,
ROM, custom chip address space, PCMCIA address space and a spare change of
clothes.

Thus, (AFAIK and I could weel be wrong...) the PCMCIA slot seems to be shadowed
over the upper 4Mb Fast RAM area 'cos there's nowhere else for it to go.
This is why some people have problems when using PCMCIA stuff and 8Mb fast RAM
(it's also why us CD32/SX1 users can't fix FMV and 8Mb Fast RAM).

When you have a 68030 accel card in your A1200, the extra bucket-loads of RAM
which they support are addressed above the base 16M area, so there is no
conflict with the PCMCIA card.


Hope this is of help to some people (one does one's best...)

TTFN,
Keith

--
          /// A M   M III GGGGG A     | Keith Blakemore-Noble, Mad Dog Software
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 \\\  /// A   A M   M III GGGGG A   A | pfloyd is a CD32/SX1, 6Mb RAM, 162Mb HD
  \\\///  Multitasking and Multimedia | which also drives a DR550, EVS1, JD800,
   \///     as standard since 1985.   | K1r, SY85, Wavestation SR and VZ1.

        PC and Windoze - the computing equivalent of a straightjacket.