#Chip ram?
16 messages in this thread
I know this is probally going to sound stupid – but what is "chip ram" as
opposed to "normal" ram? Is one type mappable – kinda sorta like MSDOS's
Expanded Memory?
Jim:
Chip memory is the memory that is accessable by the Amiga special
purpose graphics chips. The original 'Agnus' chip could address 512K bytes
of 'chip' RAM, the newer 'Fat Agnus' can address 1 meg of chip RAM, and the
newest 'Obese Agnus' used in the 3000 can address 2 megs of chip RAM. The
normal user never needs to worry about which is fast or which is chip ram,
but a programmer needs to know how he is going to use a particular piece of
memory. If he is displaying imagery, then the data needs to be loaded into
chip ram, otherwise it will not display. It is not like MS-DOS's Expanded
or Extended memory, in that it is always fully addressable, and is not
'mapped' in that sense.
Clint <VRLI> P.S. Hopefully
someone else will give a clearer explanation. 🙂
AH, kinda sorta like my dedicated display ram on my VGA card. Is there a
display mode capable of using all 2 megs of chip ram in the 3000? Jim
Jim:
Under 2.0 (on the 3000) there is a 1200×400 or some such resolution
available on the 3000. Gives you alot of room to work. My monitor on my
2500/30 is not of good enough quality to use this mode, however. (It's a
cheap Thompson monitor, good enough for programming, but not much else.)
Clint <VRLI>
That mode will NOT be flicker-fixable, even on the A3000. I believe that
1280×200 is, but then who cares? I'd much rather use 640×400! The main
purpose of 1280×400 was for video work I believe. There is 640×960, but
that is also un-flicker-fixerable.
— Ethan
Ethan, that is true, but it sure is alot of real estate to play around
with.
Clint <VRLI>
Wew should mention that the reason behinf\d the chip/fast ram dichotomy is
NOT, to keep software compatible with a 1974 8-bit microprocesso (8008) as
in MS-DOS, but to allow the CPU to be operating on fast RAM on ons 'side'
of the bus, while the coprocessors do I/O buffering, graphics ansd sprite
rendering, and audio wihi the other side of memory. This increases system
performace to such a great degree, that a color windowing GUI can run on an
Amiga 7mhz 68000, while a B&W GUI is very sluggish on an 8mhz mac. People
look as limits on chip ram as a downside of the Amiga's architecture, but
the dual bus is really brilliant. Unlike the ram on a display card, the
chip ram can be accessed by ANY applifcation in a normal way, just like the
fast RAM, with a big linear address space. Multi-tasking courtesy
dictates, that nice programs use as little chip RAM as possible, so that
everyone else can have a window too.
That's why I really like the 2 megs of chip ram on the 3000. No
excuse to run out of chip ram any more. <grin>
True, but I'd like to make a little note here that it helps to have 'true'
FAST RAM installed. So-called FAST RAM on the A501 slot in an A500, for
instance, does not perform t the dual-bus ideal. Motto: Buy external
expansion RAM if you want performance.
]Is the A501 RAM not fast because it will be Chip RAM when a super Agnes is
installed? Or is there some other reason?
It is because it is part of the Chip RAM buss, and must go through the Gary
and Agnus lines before the CPU. The expansion slot on the left is
interfaced directly to the CPU's buss. Adding RAM to the 'chip' buss that
won't be used as actual chip memory is kinda putting your money in the
second- or third-best place.
I doubt there is any display mode that would come close to using 2 megs of
chip to display a single screen.
Where the extra chip ram is useful is when you have numerous things
happening that all need chip ram. For example — at home, where I only
have 512K of chip, I have to be very careful when running high resolution
animations AND 4 voice audio simultaneously, because the graphics and sound
coprocessors are using that limited area of ram for rapid manipulation of
multiple images AND sound. So, for example, I might turn off my system
"workbench" sceen, so it isn't using any chip to hold its display in the
background.
At work, where I have 1 meg of chip (the highest you can currently get on
the 2000 series), I have only once ever run out of chip, and that was when
I was multitaksing a couple applications (all of which were using high res,
interlaced screens) AND had a high res, interlaced workbench screen in chip
ram AND tried to run high resolution animation AND 4 voice sound all at
once. With 2 megs of chip, even that would be a breeze.
Also, unlike the dedicated display on your VGA card, the chip ram is
available to the whole system, all the time. So, when you aren't involved
in the kind of system abuse I just described, it can be used for just about
anything.
Jim, please, don't use the term 'MS-DOS' around these parts, many find
it offensive. 8)
Seriously, that is an obvious question. The Amiga has NONE of the
problems which MS-DOS has regarding memory management. There is no
segmentation, no paging, no none of that.
Any data which must be referenced by the custom chip set (eg. graphics,
sound and disk buffers) must be placed in what is called 'chip ram'. The
chip ram is the only memory accessible by the custom chips. This memory is
accessed on alternate cycles by the custom chips and the CPU. This RAM is
therefore slower for non-chip set uses than is fast ram (thus the name fast
ram 8).
Currently all machines sold by dealers have 1MB of chip ram (1MB
agnus's), except for the A3000 which can have 2MB of chip ram. The A500C,
being sold by retailers like Macy's, has only 512K of chip ram. This memory
can, of course, also be used for non-chip related activities, such as
loading programs, but in general you want to use your fast-ram first.
This implies that you can get an out-of-memory error when you still have
megabytes left to spare. If a program needs to open a screen and you are
out of chip ram, even if you still have fast ram, you are out of luck.
On IBMs, there is a similar concept in that the video card will have ram
on it. The advantage is that the Amiga has a blitter which can do
high-speed manipulations on that ram and that the ram can be used for other
things as well.
The bus on the 500 and the 2000 line are 16 bits wide and 7.14MHz, a
speed related to the NTSC television standard. The 2500 has a separate bus
for high-speed 32 bit access to ram, although the chip ram must still be
accessed via the old bus. The A3000 is completely redesigned, except for
the chip set. There are now two buses: the old chip-set bus and everything
else. Chip ram is linked via both buses so that the 68030 doesn't have to
drop to the 16 bit bus to access the ram.
Finally, chip ram and fast ram are non-continuous. So, for example, if
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you have 200K of fast ram and 200K of chip ram left, and you have a 300K
file to be loaded, it cannot be loaded directly. It can, however, be loaded
in segments. Also, most programs allocate memory dynamically as they run
via AllocMem and RememberKey (?) functions, similar to malloc. This memory
need not be continuous with the program. This helps with memory
fragmentation somewhat, a serious thing to consider when using a
multitasking machine.
Anything else? 8)
— Ethan
Just butting in here with one minor correction. According to the latest
from Dave M. w/ C= Customer Support, all 500's are shipping with the 512k
agnus. The 500P's have 1meg (A501 installed) but it is 512k chip/512k
fast. The 500C's only have the 512k chip and are not shipping with the
A501's. Dave did mention that a few 500P's went out with the 1meg Agnus,
but that is no longer the case.
Jim,
In the Amiga, the custom chips can address only part of the RAM: but the
rest of the machine can work on all of it. The part of RAM: addressed by
the custom chips might be the 512K in the original Amigas, the 1M that can
now be addressed with the 1M Agnus that has been available for about a
year, or 2M in the A3000. This is very different from the MSDOS Expanded
Memory, though. The memory above the chip ram is faster, and almost all
software will use the memory above the chip ram if possible. True – if
your Amiga only HAS chip ram, everything can be done there – but if you add
more memory, the chip ram will mostly be reserved for what it does best,
and the faster
.Betty