Re: Apple II ROMs?

[mjmahon@aol.com (Michael J. Mahon)]

Ernest wrote:

(Hi, Ernest!)

>I have a question about how to determine if a Apple II clone is a clone of
>the original Apple II, or if it's a clone of a II+. I know that it's
>basically a moot question, since there wasn't much difference between a II
>and II+ board, but mostly I'm just curious about the ROMs.
>
>The original Apple II was sold with three ROMs (Monitor, and Integer Basic,)
>but no Applesoft or Autostart ROMs. Later, you could purchase those ROMs to
>make your Apple II be II+ compatible (applesoft, autostart, etc.) Is that
>correct?

Yes.

>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.

>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.

>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.

>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.

-michael

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