Re: computer video (was Re: Free IBM AT)

[Ray Arachelian]

Of course not, neither Mac, nor Lisa could display 80x25x16 or 40x25x16 
color text mode which the video makes it hard to distinguish between.  
It's nice that someone bothered to write the assembly code to do that, 
but, meh.  Truth be told, that's either a 2K or 4K display.  Compare 
that to digital camera displays whose real estate is measured in 
megapixels, and it's not all that impressive.  It's about the size of 
two icons, if that. :-)


Then again, neither could the IBM PC's CGA display do 720x384 (half of a 
printed page) black and white that looked as good.   Most you could get 
from a CGA card is 640x200x2.



Chris M wrote:


let's see if I'm allowed to post to Lisa list today. I
don't know about all that. Could an early Mac do this:

http://www.oldskool.org/pc/8088_Corruption 
 




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Re: computer video (was Re: Free IBM AT)

[Chris M]

let's see if I'm allowed to post to Lisa list today. I
don't know about all that. Could an early Mac do this:

http://www.oldskool.org/pc/8088_Corruption 

--- Ray Arachelian <[EMAIL PROTECTED]> wrote:

> Chris M wrote:
> 
> >But Apple made a mistake with
> >the Mac by not supplying a distinct video ic,
> allowing
> >the 68k to do all the work, and therefore was
> lacking
> >in speed.
> >
> 
> That's not quite true.  Both the original Mac and
> the Lisa shared memory 
> access with the video hardware.  The video hardware
> was actually much 
> simpler than what most computers used a dedicated
> display chip for.  It 
> was basically a nothing more than a shift register
> that walked memory 
> and spat out video signals. 
> 
> Half the time the CPU had access to the memory bus,
> the other half the 
> video system.
> 
> Other contemporaries of the time may have used a
> dedicated IC to do the 
> video, *BUT* in most cases, these also shared access
> to memory with the 
> CPU.  So it was no better.  Infact, they were more
> complex because they 
> were text mode (40x25 or 80x25) and needed a
> character generator ROM.  
> The video IC would read a byte from main memory,
> then turn around an 
> read the bitmaps for that character from a ROM and
> display that.
> 
> I remember there were various tricks done to get
> various styles 
> displayed too.  For the Commodore line, there were
> several bitmaps (aka 
> fonts today) that implemented primitive graphics. 
> The high bit (128) 
> was used to invert the bitmap, so the scheme to
> display the cursor was 
> to use XOR 128 on and off every second to flash the
> character.  There 
> was a patent for this simple scheme.  Other displays
> used another chunk 
> of memory that mapped along with the text to
> implement attributes such 
> as underline, flash, inverse, and another set for
> color.
> 
> Things like the VIC20 and Commodore 64 had some
> dedicated hardware to do 
> sprites and such, it's true, but for normal
> operations, it wasn't too 
> much better what the Mac/Lisa had.  There were of
> course vector systems 
> out there, but these were mostly for games and
> worked in a totally 
> different way than raster displays like om the Mac,
> Lisa, Commodore's, 
> and PC's. 
> 
> Even so, they generally had to share the memory with
> the CPU, so there 
> was a slowdown due to that.  This can be exposed on
> the Commodore 128 by 
> going into FAST mode which ran at 2Mhz instead of
> the usual 1Mhz.  The 
> 40column display would be shut off.  (The 80 column
> one which ran off a 
> chip similar to the CGA controller still worked.) 
> Even the lowly 
> TS/1000 had a fast mode that disabled the video
> because it too shared 
> it's small memory with the video system.
> 
> 
> I don't recall whether you had to do special stuff
> to access IBM PC's 
> video memory on the CGA cards, perhaps it was
> accessible in memory 
> though the video ram as it lived on the ISA card,
> but I do recall it 
> displaying snow if you directly wrote to the video
> memory and didn't use 
> the INT21 routines in the BIOS.  Lots of program
> wrote directly to the 
> screen for speed, but had to do so in the vertical
> retrace.  (The BIOS 
> routines were very slow.)
> 
> 
> The Lisa ran at 5MHz even though the 68000 was an
> 8MHz cpu due to the 
> video circuitry needing access to memory.  I'm not
> sure how they fixed 
> this for the original Mac.  Perhaps faster RAM, or
> more likely the 
> smaller screen real estate did the trick.  In some
> ways, if you look at 
> the Mac and the Lisa, the Lisa actually had
> something like 5 CPU's 
> (68000, 6504, COPS, COPS in keyboard, and an
> optional AMD/TI FPU for the 
> early I/O boards, and a Z8 in the Profile/Widget).  
>  The Mac had to 
> rely entirely on the 68000.
> 
> They could have added one more CPU just to do
> graphics, but, that would 
> have added a lot more expense and complexity. 
> Besides, in that sort of 
> system, whenever the main CPU would need to transfer
> a big chunk of data 
> to the graphics controller instead of just
> instructions that say, draw a 
> line from this point to that point in this color,
> there would be a 
> bottle neck there.
> 
> Also, back then having a dedicated video processor
> didn't mean you could 
> do graphics primitives with it.  i.e. the chips did
> not have the silicon 
> to draw lines, boxes, in "hires" bit mapped display
> modes.  Rather the 
> CPU had to do that work and there were various
> algorithms for it.  
> QuickDraw just happened to be a better
> implementation that all of those. :-)
> 
> I'm not sure many computers had video chips that
> could offload graphics 
> work from the main CPU at that stage (i.e. hardware
> accelerated 
> graphics), except maybe perhaps for the Amiga, but
> that came later on.  
> Most were just good old fashioned frame buffers in
> bit mapped mode, and 
> character generator based displays.
> 
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Moving from Maclaunch to Google Groups

[Dan Knight]

We've already moved half of our email lists to Google groups. Today 
we're starting the transition for our three non-Mac Apple-related email 
lists: Apple2list, LisaList, and Newtonlist.

If you wish to remain in the group, you must subscribe to the new 
Google Groups list. We have no way of exporting addresses from 
Maclaunch and doing this for you. I'll be updating the list FAQs, but 
you can go to one of the following pages to join:

http://groups.google.com/group/apple2list
http://groups.google.com/group/lisalist
http://groups.google.com/group/newtonlist

There are several benefits of moving to Google Groups. Although you can 
continue to treat this like a regular email list, you now gain the 
ability to read threaded postings online and, once you've logged in, 
even post replies online. You can also use Google's search engine to 
search the list archive.

On top of that, you have total control of your subscription once you've 
registered with Google. You can set your account to digest mode - or to 
"no email" mode when you go on vacation.

Best of all, we'll never have that "out of server space" problem that 
we've had so often with Maclaunch due to spam filling our mailboxes.

I think the many advantages outweigh the few drawbacks, and I hope to 
see all of you sign up in the next few days.

Dan the listmom

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