🚀 go-pugleaf

     To Bill Seymour's comments on the 2620/30 I would like to add one
comment.  If you have old (16-bit) fast memory and you buy a co-processor
board, the correct thing to do with your old fast memory is to remove it from
your Amiga.  Throw it out, sell it, anything.  If you don't, then everytime you
access that memory, your expensive coprocessor board will slow down virtually
to the speed of a 7.16Mhz 68000.  What a waste!  If you need the extra memory
(and you may well, if you were used to using all of 3-megs, you should probably
expect to upgrade to 5-megs for the '020/'030 because of things like kickstart
in RAM, bigger disk buffers so the disks can keep up to the processor etc.)
then you should sell your old memory board and buy extra ram for your
coprocessor.  Your system will run much faster and you will probably make money
on the deal.

     Oh yeah, one other thing.  If you haven't already, get a fat-agnus,
because otherwise you will have some _really_ slow memory in your memory list.

     Also, while on the topic of memory speeds, I would like to clear up some
misinformation which was tossed around recently.

     The standard Amiga 68000 cycles last 140ns.  However, a 68000 takes four
cycles to read or write memory (minimum) so that it actually takes 560ns to
read or write anything.  Half of this time is spent on the bus, and during the
other half, other chips (display chips for instance) can read from the memory.
Some memory boards may have wait states, but I'm not aware of any (for the
68000 anyway).  After all, it doesn't take very fast memory to run no
wait-states at 7Mhz, when it takes four cycles for a read.  150ns memory should
work just fine.  If there are wait states, then the time will increase to 700ns
(assuming one wait state).  Many 68000 instructions execution times are
determined by the time required to read the instruction.  Some take slightly
longer, and some, such as multiply (38-70 cycles, plus <ea> time) take far
longer.  Read the manuals for details.  The '020 can do three cycle reads, the
'030 can do two cycle reads and the '040 can (so I hear) do one cycle reads.
Personally, I'm holding out for an '050 that does zero cycle reads :-)

     So, a stock Amiga can execute a _maximum_ of 7.159/4 million instructions
per second or 1.79 million instructions per second.

.Bruce Dawson.