Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!bloom-beacon!husc6!m2c!wpi!dseah
From: dseah@wpi.wpi.edu (David I Seah)
Newsgroups: comp.sys.apple
Subject: Re: GS specific programs
Message-ID: <1300@wpi.wpi.edu>
Date: 13 Mar 89 18:44:03 GMT
References: <8903111538.AA24748@crash.cts.com> <913@n8emr.UUCP>
Reply-To: dseah@wpi.wpi.edu (David I Seah)
Organization: Worcester Polytechnic Institute, Worcester, MA. USA
Lines: 48
Keywords:

>What I dont understand is if processing the minimal bitmap slows down this
>machine so much, then why in heaven's name are all those other machines which
>process bitmaps so fast?  Is it perhaps not so much the bitmap, but the
>code that is DOING the refresh / manipulation the thing that is slow?  Or
>is it indeed that the HARDWARE implementation of the bitmap subsystem that
>is designed to run so slowly?  I am just trying to understand.  I have
>seen a SE/30 and it SCREAMS!  Now of course, the CPU is faster - but
>everyone keeps telling me in voice talks that it isnt the GS's CPU that
>is slowing down the GS, its because its doing everything in graphics.

Larry, the Apple IIGS graphics screens reside in "slow RAM".  The memory
devices involved can read/write data at the old 1Mhz speed of the Apple II+. 
So, everytime you try to put something on the screen, the 65816 gets slowed
down from 2.8MHz (assumption) to 1Mhz during those write cycles to the video
buffer.  The IIGS super hires video buffer is also 32K in size, 4x the size of
the Apple II hires screen buffer.  On the 1Mhz Apple II+, we couldn't display
a clean screen transition using assembly language without using page flipping.
 The mind boggles at what is required to update a 32K SHR screen without the
use of an extra display page, thoughtfully left out of the IIGS memory map! 
urrghghgh! I feel another flame coming on! 

Those other machines (like the Amiga) not only run twice as fast as the GS,
they also (in the case of the Amiga) have specialized hardware that is
designed to move graphics bitmaps to the screen VERY fast.  Beats the pants
off of the Apple.  It is interesting to note that the Amiga text screen is
actually a graphics mode, using alphanumeric bitmapped graphics!  So, they
have us beat in speed AND resolution.  AND they can truly multitask with
enough memory.  With a hard disk drive, the Amiga's cruddy OS actually
functions well, despite its graphic inelegance.

About the Mac SE/X (or SE/30).  According to Byte, not only is the CPU faster,
the video memory is implemented using dual-port video RAM.  Applying what
scrawny knowledge I have gleaned from this school, I think this releases
restrictions on the machine about synchronously refreshing the memory with the
video hardware, AND the video display hardware can access this memory without
any bus contention (because there are two "ports", two separate masters can
access this memory). 

I am interested too in why the GS graphics hardware is so...limited.  I have
been told that, "Oh, the slowdown is requires to maintain compatibility with
mumble mumble", but no-one tells me why.  My guess is that the Mega II was
incapable of running at higher speeds.  Why use 1MHZ DRAMs anyway unless the
Mega II couldn't handle anything faster? 

Gee, no flames!  I'm maturing!  Yay yay yay whee whee whee whoop!

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