Conference hydra::amiga_v1

    The Amiga has many different graphics modes...
    
    320 x 200 w/32 colors out of 4096
    320 x 400 w/32   "     "      "
    640 x 200 w/16   "     "      "
    640 x 400 w/16   "     "      "  
    
    32 color modes are achieved by the use of 5 bit-planes, and 16 colors
    require 4 bit-planes.  The programmer has the option of using as
    little as one bit-plane if he likes.
    
    The Amiga display hardware is capable of 6 bit-planes, which is
    required for Hold-and-Modify mode.  In HAM mode, all 4096 colors are 
    displayed on screen at once.  If you've ever seen any Digi-View
    images, you'll see that they are of near-photographic quality.
    
    All Amiga models currently have the same graphics capabilities,
    with the exception that the A500 and A2000 have a monochrome composite
    output, versus the color composite of the A1000.  The monochrome
    composite of the A500 is intended to allow 16 grey scales on an
    inexpensive monochrome composite monitor.
    
    The 512K of ram that comes installed in the A500 is CHIP ram, in
    that the custom graphics and sound chips can only access data that
    reside in the lower 512K.  Memory from 512K to 2 megs is reserved
    for future enhanced graphics chips.  Memory from 2 megs to 8 megs
    is reserved for autoconfiguring FAST expansion ram.  The 1 meg A500
    actually uses ram that is not truly FAST, in that it resides on
    the custom chip buss.  This means that if an application uses lots
    of pixels or bit planes, there may be some slowdown due to contention
    between the custom chips and the program code for clock cycles.
    This slowdown is hardly noticeable, and is NEVER greater than the
    slowdown experienced by an unexpanded 512K Amiga.
    
    Real FAST ram can be added to the A500 through the expansion buss,
    just like on the A1000.  When FAST ram is added, the application
    automatically loads program code into FAST ram, and graphics code
    into CHIP ram.  In this case, the AMiga will always run at maximum
    speed, regardless of how intensive the graphics may be.
    
    Early in the life of the Amiga, many detractors, most notably the
    Trameils of Atari, made a big deal over contention problems in the
    Amiga.  All their claims were wildly exaggerated.  In fact, in any
    of the graphics modes that the ST allows, there is no slowdown even
    on an unexpanded machine.
    

    There were a few misleading statements made in [.1]
    
    First, the number of colors represents the MAXIMUM # of bits planes
    permissible for each resolution. One of the better features of the
    Amiga is allowing you to have fewer bit planes if you don't need
    all that color. This means that if you only need 4 colors in the
    standard workbench type screen, you use 1/2 the memory (2 bits per
    pixel instead of 4) and there is NO bandwidth contention -- ie,
    the processor is never blocked by the video. A HAM mode picture
    or 640 x 16 colors (whether interlaced or not) will require so much
    bus bandwidth for screen updating that the processor will really
    only get to touch CHIP RAM during horizontal and vertical blanking.
    Of course, that's the nice thing about fast RAM -- since video doesn't
    have access to all of memory, FAST RAM is always fast no matter
    how loaded the video.
    
    Another mistake: 8M is allocated fast RAM. The 1M is located at
    C0000000. However, the largest autoconfigurable device is 6M, so
    if you have an 8M board, it has to autoconfig as 6M and 2M. That's
    probably what caused the confusion.
    
    See the note I posted on sharing PD software!
    
    Thanks,
    dov

    Sorry if I misled anyone in .1; I thought I said that the application
    could use as little as one bit plane in any screen res.
    
    Also, I dont have an Amiga memory map nearby;  I believe that the
    WCS or system rom resides at the very top 256K of the addressable 16
    megs, and that the top 1 meg is reserved for future, larger roms.
    What is reserved for the space from 15 megs on down?  (Sorry,
    I don't speak hex).

    First,I want to thank you that you answered my questions .
    
    I got much information out of your replies.Perhaps I will buy an
    Amiga-500.But I have another question :
    What can be connected to the A500 ? I have a 5 1/4" disk-drive 
    ( 48 tpi ).Is it possible to plug it into the disk-connector at
    the back of the computer? Or can just 3 1/2" disk's be connected?
    Or must I buy an external diskcontroller first ?
    Some Notes ago I read about replacing the 68000 by the 68010.
    Is this possible in the A500 too?
    
    Thanks,
           Peter
    
    

    Not only is is possible to directly plug in a 68010, but CSA and
    Gemstone are both shipping cards that have a 68020/68881 chipset
    installed.  The 68020/68881 cards go for around $750 fully loaded.
    These cards use the Amiga's 7.14 MHz clock, but more expensive versions
    are available that use a 14.28 MHz clock and are socketed for 32
    bit ram chips.
    
    Surprisingly, all these boards will fit right inside of the A500,
    also.  Didn't think there'd be that much room in there.
    
    I've been using a 68010 for about 9 months in an A1000.  There are
    only three titles that I know of that don't like the 68010;
    Transformer, Barbarian, and TextCraft Plus.  There is a simple PD
    patch called 'decigel' that invokes some sort of trap for the illegal
    instruction that these naughty programs use.
    
    The speedup that the 68010 provides isn't very noticable, maybe
    5-8%.  Some things the 68010 does very quickly, like moving data
    from FAST to CHIP ram.  Somethink like 50% faster.   For $20 and
    a half hour of your labor, the 68010 is a pretty cheap way to get
    a bit more speed.
    

    RE: .4
    
    yes, you can plug in a 5 1/4" disk-drive.  A couple magazines have
    published articles describing how to do it.  Commodore also sells
    an external 5 1/4" drive, primarily for use with the Transformer,
    but it can be used under AmigaDOS as a, i think, 440K disk.  Needs
    to be able to do more TPI to be a 880K disk.
    
    A second 3 1/2" disk is more useful.  You can daisy chain your
    5 1/4" disk from it.  The disk controller in the computer can
    handle up to 4 disk drives.
    
    -dave

    re .4
    The only difference between the 5.25" and the 3.5" electrical signals
    is that the 3.5" expects one signal latched. One chip, and about
    5 connections does it. You will need a power supply though. The
    A-500 power supply is VERY weak, and I wouldn't recommend even boards
    sucking power, let alone a floppy.
    
    Incidentally, there is a lot of room in the 500. I saw the guts
    6 months ago when some Commodore engineers proudly showed it at
    a club meeting in JAUG (Perry Kivolovitz, et al) The parts count
    has been reduced to 5+RAM. If you've ever looked at the inside of
    the 1000, you've got to appreciate that. I'm positive the machine
    is more reliable. Anyway, there is almost nothing in the box, but
    the closed space and comparative lack of ventilation (no fan) would
    have me worrying about putting in 32 DRAMS and a hairdrier 68020-68881
    combination. Those suckers RADIATE! :-) Plus, where would the power
    come from? I'd think you have to get a new power supply with it.
    
    dov

If you get a 720K 5.25" drive (comparatively cheap)
    that can go one-for-one with the 3.5" ie -- IBM is conservative,
    and the Amiga is not -- it will put 880K on it instead of 720K.

    re: .7 its more than one chip; the schematic is in the
    schematic/expansion docs available from CBM.
    John

    re: .7
    
    i've heard one of the "advantages" of the A500 design is the power
    brick - you can upgrade your power supply without having to open
    the computer.  Don't know of anybody offering a bigger power
    supply for the A500 currently.
    
    -dave

Re: .2

>    Another mistake: 8M is allocated fast RAM. The 1M is located at
>    C0000000. However, the largest autoconfigurable device is 6M, so
>    if you have an 8M board, it has to autoconfig as 6M and 2M. That's
>    probably what caused the confusion.

You are incorrect about there being no support for 8 meg autoconfigure.
The memory sizes supported by the Amiga Expansion Architecture are:  64k,
128k, 256k, 512k, 1M, 2M, 4M, 8M.  (This information is taken straight from
page 5 of the "Amiga Expansion Architecture" paper in Commodore's book
"Schematics and Expansion Specifications.")

Note that there is no support for 6 Meg expansion devices.  The 8 Meg card
from ASDG does support a 6 Meg configuration by way of the mechanism you
described: it configures as a 4 Meg board and another 2 Meg board.

The Amiga memory map (minus uninteresting device assignments and holes) is:

Addresses	(size)	  "Commodore's comments."  My comments
-------------	-------	  ------------------------------------------------
000000-07FFFF	(512k)	  "Chip memory"

080000-1FFFFF	(1.75M)	  "Do not use"  The Amiga 500 and 2000 stick their
			   other half of meg of memory here.  The Insider
			   type boards live here as well.  Everyone knows
			   that all of this memory area will be chip memory
			   someday.

200000-9FFFFF	(8M)	  "Fast Memory"  This is the normal expansion memory
			  that Amiga 1000 owners have been sticking on their
			  machines.

A00000-BEFFFF		  "Do not use"

C00000-DFEFFF	(2M-4k)	  "Reserved for Future use"  However, the Byte by
			   Byte Pal Jr. stuck its 1 Meg of memory here.  I
			   believe that the 32 bit wide memory from CSA
			   goes here as well.