Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!samsung!olivea!tardis!jms
From: jms@tardis.Tymnet.COM (Joe Smith)
Newsgroups: comp.sys.amiga.introduction
Subject: Re: MONTHLY POSTING: Frequently Asked Questions and Answers V1.2 (April 1991)
Summary: More "RAM" definitions.
Message-ID: <1682@tardis.Tymnet.COM>
Date: 31 Mar 91 09:44:20 GMT
References: <8990@chorus.fr>
Reply-To: jms@tardis.Tymnet.COM (Joe Smith)
Organization: BT Tymnet, San Jose, CA
Lines: 58

In article <8990@chorus.fr> ferry@chorus.fr writes:
>     1.7.    What is the difference between al these kinds of memory?

Here's how I would describe the various type of memory.
			--------------
Chip RAM = Memory that can be accessed by the Amiga's custom chips.  All
graphics images (screens, windows, sprites, etc) must be in Chip RAM to be
displayed.  Likewise, all audio samples must be in Chip RAM to be played.
On the original Amiga, only the first 512K bytes of memory could be accessed
by the custom chips.  Newer A500 and A2000 systems come with 1 meg of Chip
RAM, and the A3000 can be upgraded to 2 meg of Chip RAM.

Slow RAM = Alias for Chip RAM.  Anytime the custom chips need to access
Chip RAM, they have priority over the CPU's access to that memory.  In
particular, displaying a hi-res screen of 640x400x16-colors will lock out
the CPU about 80% of the time.

Fast RAM = Anything that is not Slow RAM.  This includes both Autoconfig
RAM and 32-bit RAM.  Programs run faster when the executable code is loaded
into Fast RAM, since the 68000 CPU is not competing with the custom chips.

Slow-Fast RAM (aka C00000 RAM) = An unfortunate side effect in the original
A500 and A2000 implementations.  They came out with a "Fat Agnus" that only
knew how to talk to 512K, even when 1 meg of memory was installed.  This 2nd
512K was like Fast RAM in that it could not be used for graphics and sound,
however, it was just as slow as Chip RAM.  The A501 RAM/Clock card for the
A500 is Slow-Fast RAM on a machine without the "1-meg Agnus".

Expansion RAM = Additional memory, either AutoConfig RAM or AddMem RAM.

AutoConfig RAM = Expansion RAM that automatically identifies itself when
the Amiga is booted.  It is designed to fit into the 8-meg address space
between 200000 and 9FFFFF, and usually comes in 2-meg, 4-meg, or 8-meg
sizes.  Memory boards for the A2000 are AutoConfig RAM.

AddMem RAM = Expansion RAM that is not known to the Amiga until the AddMem
(or similar) program is run.  Most memory boards for the A1000 are AddMem
RAM, since the AutoConfig process was not defined when the A1000 came out.

NoFastMem = A program that optimizes things on an Amiga with a combination
of Chip RAM, AutoConfig RAM, and Slow-Fast RAM.  It rearranges a system list
such that when a program tries to allocate memory (and does not specify that
it needs Chip RAM or Fast RAM), the memory will be allocated from Expansion
RAM in preference to Slow-Fast RAM.  It keeps things running faster longer.

32-bit RAM = High speed memory mounted on a 68020 or 68030 processor upgrade
board.  It also applies to the Fast RAM on the A3000 motherboard, and memory
boards conforming to the Zorro-3 specification.  It allows the 32-bit CPU to
access 32-bit quantities in a single memory cycle, instead of as two 16-bit
cycles.  Since one cycle is faster than two, the 68020 or 68030 CPU runs
faster if it has 32-bit RAM available.  In most cases, 32-bit RAM cannot be
accessed by A2000-compatible DMA devices (such as disk controllers) because
Zorro-2 boards are limited to 24 address bits.
-- 
Joe Smith (408)922-6220 | SMTP: jms@tardis.tymnet.com or jms@gemini.tymnet.com
BT Tymnet Tech Services | UUCP: ...!{ames,pyramid}!oliveb!tymix!tardis!jms
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San Jose, CA 95161-9019 | humorous dislaimer: "My Amiga 3000 speaks for me."