A: To a limited degree,
yes. Amiga system ROMs differ in size and in
features.
The following list illustrates
compatibility of different models with
different ROM sizes:
- Amiga 1000: 256 KB (copied from
"Kickstart" disk)
- Amiga 3000, 4000, 4000T: 256 KB, 512 KB
(on two ROM chips)
- Amiga 500, 500 Plus, 2000: 256 KB,
512 KB, 1 MB (single ROM chip)
- Amiga 600: 256 KB, 512 KB, 1
MB, 2 MB (single ROM chip)
- Amiga 1200: 256 KB, 512 KB, 1
MB, 2 MB (on two ROM chips)
Emulated systems may overcome some of the
above limitations by supporting 1 MB and 2
MB ROMs on a wider range of emulated Amiga
models.
Some hardware-specific features also
differ between models. ROMs designed for AGA
chipset Amiga systems (Amiga 1200, 4000) do
not support certain ECS chipset features
such as ECS Super Hires modes. Conversely,
ROM versions prior to 3.0 do not support AGA
chipset features. Amiga
scsi.device functionality also differs
between models: the Amiga 600 and 1200 share
the same code, but the Amiga 3000, 4000 and
4000T each require a version tailored for
the respective hardware. Amiga 3000 ROMs may
further access hardware unique to the Amiga
3000, and will fail on other systems
(emulated or "real").
The scsi.device found on Amiga 4000 (IDE)
and 4000T (IDE and SCSI) ROMs checks for
existing device names in Exec's DeviceList
and sets itself to the first available free
name, e.g. "scsi.device", "2nd.scsi.device",
"3rd.scsi.device", etc. (up to
"8th.scsi.device"). This may explain a
change in device names when different ROMs
are used.
The ROMs for the 68000-based systems
(Amiga 1000, 500, 500 Plus, 2000, 600) are
largely interchangeable. Amiga 600 ROMs
additionally include scsi.device,
card.resource and
carddisk.device modules for built-in hard
disk and PC Card support. These modules
check for the presence of the Gayle custom
chip (which in the Amiga 600 and 1200
replaced the Gary chip) and fail gracefully
if it is not found. This is the case for
example for the 3.1 and 3.X ROMs, where the
68000 build incorporates features for the
Amiga 600, but is also designed to run on
other models with the same CPU, like the
Amiga 500 and Amiga 2000.
The ROMs for 68000-based systems (Amiga
1000, 500, 500 Plus, 2000, 600) can in
general also be used on newer systems,
except for their graphics.library not
supporting AGA features and
expansion.library not supporting 32-bit Fast
RAM (unless such RAM came with its own ROM
to add the RAM) and Zorro III cards. The
Amiga 600 scsi.device should also work on
the Amiga 1200 (but not on the Amiga 3000 or
4000).
Certain third-party peripherals like
Phase 5 CPU cards limit support to 512 KB
ROMs when using their "MapRom" option.
Other peripherals may also affect
compatibility. For example, FFS partitions
larger than 2 or 4 GB (depending on the
controller and device) and hard disks
larger than 4 or 8 GB are only reliably supported from
scsi.device version 43 (3.X ROMs in Amiga
Forever).
Amiga OS versions up to 1.3 used 256 KB
ROMs. Starting from the "1.4" beta series
(which was later officially released as
2.0), 512 KB ROMs were used. CDTV and CD³²
systems use an additional expansion ROM (256
KB on the CDTV, 512 KB for the CD³²) to host
CD access and other console-specific
features.
In order to keep using 512 KB
Amiga OS 3.1 ROMs on the Amiga 4000T
("Tower") model, which needed to fit
additional code to support the dual IDE and
SCSI interfaces in ROM, the
workbench.library was moved from ROM to disk
and a small "WBFind" module was added in its
place, to load workbench.library from any
disk. Amiga 4000T ROMs contain also work on
the Amiga 4000, as long as there is a
disk-based workbench.library.
Amiga Forever 512 KB "3.X" ROMs employ the same technique used for
the 4000T ROMs, freeing ROM space used by
workbench.library to make room for other
enhancements. Amiga Forever 1 MB "3.X" ROMs
(for Amiga systems which support 1 MB ROMs)
instead include both workbench.library and
the other ROM enhancements.
Some ROMs included in early versions of
Amiga Forever included "illegal opcodes"
that were implemented in emulated systems
since 1997, but which were not supported on
the original hardware. ROMs included in
newer versions of Amiga Forever do not use
"illegal opcodes".
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