Re: Apple II ROMs?

[Ernest <leucoplast@seanet.NOSPAM.com>]

Michael J. Mahon wrote:

> Ernest wrote:
> 
> (Hi, Ernest!)

Hello, Michael!

>>If I have an early clone motherboard which only has three ROMs, is it
>>reasonably safe to assume that it was built as an Apple II clone, rather
>>than a II+ clone?
> 
> It depends on whether the ROMs are 2KB ROMs or larger.  If they
> are 2KB (like Apple ]['s and ][+'s) then it sounds one ROM short of
> a picnic.  ;-)  If they are 4KB ROMs, then three is enough to hold
> Applesoft in addition to the F8 (Monitor) ROM.
> 
>>For example, if I have a clone board that is laid out like an Apple II
>>board, and it has the six ROM sockets but only three are being used
>>(D0,E0,F0,) I would assume that that system is meant to be a clone of the
>>II+, and that the owner would provide his own D8,E8,F8 ROMs. Correct?
> 
> No, that may mean that each ROM is 4KB, and is almost certainly
> a ][+ clone.  (A quick turn-on with a monitor should verify that, if it
> is working...).
> 
> Very likely, this clone was made to use either 2KB or 4KB ROMs,
> and has 4KB ROMs installed (probably 2732's).
> 
>>But... if I have a clone board that only has the initial three ROMs, and
>>no room for expansion, should I assume that it's meant to be a clone of
>>the original Apple II? I guess that they could have used larger capacity
>>ROMs which would hold more information but I'm not sure? If they used 32k
>>ROMs instead of 16k ROMs, could they have the Autostart and Applesoft code
>>included into those ROMs (D0,E0,F0?) Would that work, as far as addressing
>>is concerned?
> 
> Exactly.
> 
> BTW, a 32k (bit) ROM is usually organized as 4Kx8, or 4KB(ytes), etc.

My ignorance of this stuff is showing, eh? I assumed that a 2732 was a 32k
ROM, and the 2716 was 16k. 
 
>>I have one late model clone board that only has the Monitor ROM on the
>>motherboard, and two additional ROMs on an expansion card. The card ROMs
>>are different sized -one 16k and one 32k. The card has room for two
>>additional ROMs but they were never added. However, the system Autostarts
>>from a disk drive, and it loads Applesoft on startup (with no disk in the
>>drive.) I don't understand how they were able to do so much with those two
>>ROMs?
> 
> Are you sure that the ROM on the main board is only 2KB?  It may be
> a 2764, which is a full 8KB--plenty for Applesoft and the monitor.  The
> additional ROMs on the plug-in card may not even be involved.  Try
> removing the card and see if you still have Applesoft.

No, I haven't checked the size of the on-board ROM. You are probably correct
about the size. I'll have to look at that now that I understand it a little
better.

>>I have a Basis 108 that uses six 32k ROMs. Each ROM is somehow divided
>>into two halves. By using a switch before startup, the system can be set
>>to use either Basis Basic or Applesoft. In otherwords, each of the six
>>ROMs contains code for both versions of Basic. Could the six Basis Basic
>>ROMs be compressed into three 32k ROMs instead of six 16k ROMs? Or does
>>the computer look for different parts of the software at different address
>>locations?
> 
> It could be, but the Basis is designed to address only 2KB per ROM socket,
> with a switch (soft or otherwise) controlling the high-order address pin. 
> This allows either the low 2KB or high 2KB of each 4KB ROM to be selected
> by flipping the switch.

That makes sense. So do both the 2716 and 2732 ROMs have High and Low areas?
My Basis is using six 2732 ROM chips because the 2716 wouldn't work for
what they were trying to do. I have copies of the modified ROM contents if
you want to look at them, as a .DSK image.
 
>>If a board does not have an Autostart ROM (or expansion room for one) can
>>you use work around that problem by using a ROM expansion card, like those
>>old six ROM cards that I've seen on ebay?
> 
> Yes, that should work.

Thanks for your help.