Re: If you could design a $300 homecomputer today, what would you choose?

[Roy Miller <millers@inebraska.com>]

william strutts wrote:

> "Roy Miller" <millers@inebraska.com> wrote in message
> 3B537CB9.D08CB935@inebraska.com">news:3B537CB9.D08CB935@inebraska.com...
> > william strutts wrote:
> >
> >
> > But he mentioned 4-8 megs of RAM, which is VERY doable with a 68000, and
> the
>
> This is true but the other memory is still memory and has to be accessed
> in some manner.  Plus we are talking about a sub-300 dollar machine
> and any custom logic is going to cost money.
>
> > 64-256 as battery backedup RAM disk for documents. As RAM disk, the
> address
> > lines aren't the issue. You can have 1 meg RAM disks with the Apple ][+.
> >
> Oh really.

Really. I have a 1 meg RAM card in my ][+. There were a number of such cards
sold. And some were battery backed. 16 address lines, 8 bit bus and 20 bit
address space.  Surely you have seen such in ads. And since that was done
with an 8 bit 6502, I'm sure the 16/32 bit 68000 could do it too.

> You still have to get stuff in and out of your RAM disk and it
> takes address lines.  You will still need an address decoder to be able
> to switch banks of RAM in and out of main memory.

RAM disks aren't part of your main memory. DUH!! Do you bother to read any of
the posts being made? The software that organizes the RAM disk is in your
memory, but as far as the CPU is concerned, that chunk of RAM is no different
than a hard disk or floppy disk. Or do you wish to assure that disk drives
are also part of the CPUs memory, being switched in and out?

> It doesn't happen
> like magic.  A real address in memory must somehow find its way
> to the correct bank of RAM that you want to access.  It is a real
> pain in the butt doing it that way.  The Apple II couldn't address
> more than 64K or RAM at any one time anyway.  Programs
> never exceeded the size of memory space.

Wrong! Programs often exceeded memory space. It was called overlaying. Ever
hear of WordStar? And yes, that was a Z-80 program, but 6502 programs did the
same thing. The overlays were on disk, called in to replace a part of memory
(much like bank shifting, but much, much slower). With a RAM disk, exactly
the same thing happened, only the data/code was stored in RAM outside the
memory space of the CPU, and organized as a RAM disk.

The Coleco ADAM did this, so did the Atari 130 XE. There were plenty of
boards like this for S-100 computers using the Intel 8080 or Zilog Z-80. In
fact it was the best way to use CP/M Wordstar. Some would say, the ONLY way
to use WordStar.

> The 68K is a totally
> different animal.  Programs can be huge on a 68k machine.  I don't
> think you would want to bank switch RAM to run a program.

No one was talking about bank switching.
He was talking about a 64-256meg battery backed RAM disk though.

Roy

>
>
> --
> --
> William R. Strutts - wrstrutts1@nospam.home.com - Whatever!
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