Accelerator Cards
24 messages in this thread
I am the owner of a 2000HD. I would like to upgrad my processor for 3D
modeling purposes. I am searching for advice about which card to buy. I
do not want to buy more processor than I need or spend a fortune doing it.
I know GVP makes a an upgrade as well as PPS, VXL and CSA. I do not need
an SCSI controller as I already have the 2091A card. I am confused about
the relative virtues of the 68020 vs 68030 and how they would be applicable
to my system. A Byte magazine article implied that the 68030 was nothing
more than the 68020 with a built in MMU. If so, is it an advantage for me
to have such a thing. Do I already have a MMU in my system? Could I get
along without it on a card? Would a 68030 run more quickly than a 68020 at
the same speed assuming I kept my present system configuration ( 1MB chip
2MB Fast (16 Bit))? How much of an advantage is 32 bit RAM? How great an
improvement in rendering speed will I obtain by having a math coprossesor
assuming my software package supports it?
The economy version of Mega Midget Racer is advertised at $399 for a 25 MZ
68030 without MMU. Is this a good buy? What is MMU and what good is it to
me?
Thanks for answers to my dumb questions.
Lee DeWitt
Lee,
The differences between the 68030 and 68020 are more than just the
built-in MMU. The 68020 has only a 256 byte instruction cache, whereas the
68030 has both a 256 byte instruction cache and data cache. The caches
permit the processor to work with instructions and data held within the CPU
rather than fetching it from main memory, which speeds up processing
dramatically. However, the bulk of the improvement is contributed by the
instruction cache, which both CPUs have. The MMU has limited use on the
Amiga currently. Mainly it can be used to copy the DOS ROM image into 32
bit RAM (if you have any) which further enhances speed, particularly for
anything using ROM calls. Inasmuch as most graphic primitives are in ROM,
it helps speed up graphic operations substantially. Your computer does NOT
have an MMU. Either the accelerator card has it or you are without.
Perhaps in the future a later version of the OS may implement virtual
memory, which would need an MMU, but right now there is little need for it
except as I mentioned previously. The enhancements of an accelerator card
will be further benefited by having 32 bit RAM. You can expect to spend an
additional $400 or so for a RAM card for the MegaMidget with 2 meg of RAM
and about $600 for 4 meg. This is in addition to the accelerator. If you
buy a card with RAM included, such as the GVP cards, you can expect to pay
about what a MegaMidget with the RAM card will cost. If you would like a
cheap alternative, I have an older Hurricane 68020 card with 4 Meg of 32
bit RAM and 68881 FPU (operates at 14 Mhz) for $500.
Thanks for your reply. I wish all the questions I have left on boards have
been answered as comprehensively. Do you know what the economy version of
MMR is that is advertised for $399? Also, with respect to the MMU. Is
this necessary to have if the board is also to utilize the 3 Meg of native
RAM that I already have? That is, assuming I get 32 bit RAM with the
accelerator, will the card be able to access my RAM without the MMU?
Thanks for reply Lee
Lee,
The economy version doesn't have an MMU, and one cannot ever be
added to the board. That's why it's cheaper, the CPU used is a special
version of the 68030 which doesn't have an MMU in the chip. You don't need
an MMU for anything, really. If you install a 32 bit RAM card the 68030
will use the 32 bit RAM and it will also use any 16 bit RAM you already
have installed. That is independent of whether you have an MMU or not.
What you cannot do without the MMU is map the AmigaDos ROMs into 32 bit
RAM, which makes the Amiga's graphic primitives run much faster. If you do
a lot of graphic processing, then you might prefer to get an accelerator
with an MMU to take advantage of the speed increase the ROM mapping will
provide. Perhaps in future versions of AmigaDos the MMU might be employed
for virtual memory or to enable applications to protect portions of memory
using the MMU, but right now only ROM mapping is available, so far as I
know, which needs the MMU.
The MMU can also be used to prevent certain key areas of ram from being
cached. This can be important for memory mapped peripherals.
David
David,
Yes, that's true, but are there any applications currently doing
that, other than ROM mapping and Enforcer?
Steven,
I don't know about any applications, but, there could be some present or
future system software that uses it in that fashion. The BridgeBoards,
with the Janus memory is a natural for such an action. And, ROM mapping and
Enforcer are nothing to sneeze at, either. IMHO, it's like painting
yourself into a corner to get an 030 w/o the MMU, but I acknowledge that
there may be some overriding financial conditions in some cases. If that
were the case, my personal choice would be to wait a bit until I could
afford the full unit, but, your mileage may vary.
David
David,
I agree about the possible future needs. But the person was more
concerned about whether there were immediate needs for the MMU. I advised
him to get the board with an MMU since that would provide the best upgrade
path depending upon whether he was willing to spend the extra cash.
When you say that mapping the ROM to RAM speeds up the graphics primitives,
how valuable would this be to an application such as 3D modeling or ray
tracing? I would imagine those programs spend most of ttheir time
calculating although I've noticed that some complex wireframe shapes take a
while to redraw. Would remapping have a serious improvement here.
Thanks for your help. I'll probably get a 25 MZ 68030 first and then add
in the 32 bit RAM if it seems worth it. I'm undecided about whether I need
the MMU or not. Since it probably can't be added later I suppose it makes
sense to get a card with it. Or maybe not. I'll have to think about it.
Probably just the improved processor is all I'll really need.
Thanks again Lee
Lee,
As an example. On my system mapping ROM to 32 bit RAM results in
an almost threefold increase in the speed it takes to set and reset pixels
in a test of SetPixel() function. Ray tracers will benefit from both the
ROM mapping and a FPU, if it uses floating point math. A FPU can result in
at least a tenfold increase in the speed of floating point math operations
if the software uses the FPU. I would certainly recommend an accelerator
with a 68881 or 68882 FPU unit. The benefit of ROM mapping will only be
had if you have 32 bit RAM and the MMU. If you are going to buy a new
card, buy the fastest you can comfortably afford. And be sure the card can
accomodate 32 bit RAM, even if you don't get any to start. A good starter
card is the GVP 22 Mhz Combo. It comes with some 32 bit RAM (1 or 2 meg)
and has a 68882 FPU. RAM can be expanded up to 16 meg, I think. Street
price is around $750.00 (for the 2000s only). If you have a 500, then you
will need something like the MegaMidget.
I will definetly get the math coprossesor. Thanks for your help.
Lee
Lee:
Without the MMU & 32bit memory most if not all of the advantages of having
an '030 are lost. As far as I'm concerned Selling an 030 without a MMU is
strictly an advertising gimmic, and the 32bit memory is really needed, as
it's where most of the speed increase comes from (the 68030 has lots to do
with it too, but without the 32bit memory it will be doing lots of waiting
for the memory, so the increase won't be seen as much).
-Mike Schiller
In sunny Fort Lauderdale
I guess I'm settled on a 68030, 32 bit memory and a MMU. I'm glad I asked
about this as I was really in the dark with regard to the whole subject. I
have a year and a half of back issues of Compute and Amiga World but there
was only 1 accelerator review.
Incidentally, with regard to compatability, when producers state their
board has a fallback mode to the 68000 exactly what does this mean? Is it
actually the 68000 on the card as well, or the 68030 acting like a 68000?
If the latter, at the original speed or the accelerator speed? I would like
to have complete backward compatability with all the software I already
own.
Thanks for your reply, Lee
Lee:
When they say that their boards have a fallback mode to 68000 it means
exactly that, the system goes back to operating on the original 68000 at
the original speed 7.16mhz just as if there was no accelerator in the
machine.
-Mike Schiller
In sunny Fort Lauderdale
The MMU also lets you get more memory out of the AMAX II Mac emulator box.
>>>> Ron Legro / Milwaukee via WHAP!
"Wherever you go, there you are!"
Ron,
I think you'll find that if you have the MMU and memory at C00000
that the MMU will enable you to add that memory for use by AMAX, true. But
if you have normal fast ram, then you don't need tthe MMU for full use of
available ram. I have 9 meg of ram, all contiguous, and AMAX fully
utilizes it without the need for the MMU. But you are right, the MMU does
have an application with AMAX. I had forgotten about that one.
Steven: Yeah, I know you can get AMAX to grab all your RAM without a MMU,
but my understanding was that it would actually make productive USE of all
that RAM and act with more Mac compatibility with a MMU. >>>> Ron Legro /
Milwaukee via WHAP!
"Wherever you go, there you are!"
Ron,
You may be right, although I'm not sure if that's not the case
anyway. On my system, before I got the GVP accelerator, I used a Hurricane
68020 card which didn't have an MMU, but did have 4 meg of 32 bit RAM.
However, none of the fast ram in my system was at C00000,the so-called
"slow" fast ram area. The system had 9 meg ram in total, not contiguous.
Yet, AMAX used it all. I had 6 meg allocated to Mac and the balance as a
ram drive, and the Mac seemed to find and use all the ram, or at least
that's what it seemed to do. Later, I got a GVP accelerator with the MMU
on board. I don't notice any real difference in what AMAX does whether I
set memory to MMU or User, it still appears to work the same. If there is
a difference, and I know the manual discusses it, I don't seem to notice
it. The manual suggested that{ if your ram weren't contiguous that AMAX
wouldn't be able to fully utilize it, or something to that effect. But, I
wonder if later versions of the AMAX software haven't resolved that
"problem" or if I am just confused as to whether AMAX is really using all
my allocated ram.
Steven: Maybe it doesn't have so much to do with finding the RAM as not
getting confused while it uses all of the RAM. I've had a few hang-ups with
AMAX if I set the RAM disk too low. >>>> Ron Legro / Milwaukee via WHAP!
"Wherever you go, there you are!"
Ron,
You may be right. I have never had the memory stressed while in
AMAX with lots of apps running. Perhaps, I should try using the MMU
setting and see what goes on, perhaps I've been missing something!
Wouldn't be the first time.
Ron,
Should we start calling you "Buckaroo" Legro?
Excuse me, Steven, but I was led to believe all you have to do to upgrade
to MMU with one of the economy boards is to replace the 68030 "EC" chip
with a standard 68030 chip. >>>> Ron Legro / Milwaukee via WHAP!
"Wherever you go, there you are!"