amiga
<computer> A range of home computers first released by
Commodore Business Machines in early 1985 (though they did
not design the original - see below). Amigas were popular for
games, video processing, and multimedia. One notable
feature is a hardware blitter for speeding up graphics
operations on whole areas of the screen.
The Amiga was originally called the Lorraine, and was
developed by a company named "Amiga" or "Amiga, Inc.", funded
by some doctors to produce a killer game machine. After the
US game machine market collapsed, the Amiga company sold some
joysticks but no Lorraines or any other computer. They
eventually floundered and looked for a buyer.
Commodore at that time bought the (mostly complete) Amiga
machine, infused some money, and pushed it through the final
stages of development in a hurry. Commodore released it
sometime[?] in 1985.
Most components within the machine were known by nicknames.
The coprocessor commonly called the "Copper" is in fact the
"Video Timing Coprocessor" and is split between two chips:
the instruction fetch and execute units are in the "Agnus"
chip, and the pixel timing circuits are in the "Denise" chip
(A for address, D for data).
"Agnus" and "Denise" were responsible for effects timed to the
real-time position of the video scan, such as midscreen
palette changes, sprite multiplying, and resolution
changes. Different versions (in order) were: "Agnus" (could
only address 512K of video RAM), "Fat Agnus" (in a PLCC
package, could access 1MB of video RAM), "Super Agnus"
(slightly upgraded "Fat Agnus"). "Agnus" and "Fat Agnus" came
in PAL and NTSC versions, "Super Agnus" came in one
version, jumper selectable for PAL or NTSC. "Agnus" was
replaced by "Alice" in the A4000 and A1200, which allowed for
more DMA channels and higher bus bandwidth.
"Denise" outputs binary video data (3*4 bits) to the "Vidiot".
The "Vidiot" is a hybrid that combines and amplifies the
12-bit video data from "Denise" into RGB to the monitor.
Other chips were "Amber" (a "flicker fixer", used in the A3000
and Commodore display enhancer for the A2000), "Gary" (I/O,
addressing, G for glue logic), "Buster" (the bus
controller, which replaced "Gary" in the A2000), "Buster II"
(for handling the Zorro II/III cards in the A3000, which meant
that "Gary" was back again), "Ramsey" (The RAM controller),
"DMAC" (The DMA controller chip for the WD33C93 SCSI adaptor
used in the A3000 and on the A2091/A2092 SCSI adaptor card for
the A2000; and to control the CD-ROM in the CDTV), and
"Paula" (Peripheral, Audio, UART, interrupt Lines, and
bus Arbiter).
There were several Amiga chipsets: the "Old Chipset" (OCS),
the "Enhanced Chipset" (ECS), and AGA. OCS included
"Paula", "Gary", "Denise", and "Agnus".
ECS had the same "Paula", "Gary", "Agnus" (could address 2MB
of Chip RAM), "Super Denise" (upgraded to support "Agnus" so
that a few new screen modes were available). With the
introduction of the Amiga A600 "Gary" was replaced with
"Gayle" (though the chipset was still called ECS). "Gayle"
provided a number of improvments but the main one was support
for the A600's PCMCIA port.
The AGA chipset had "Agnus" with twice the speed and a 24-bit
palette, maximum displayable: 8 bits (256 colours), although
the famous "HAM" (Hold And Modify) trick allows pictures of
256,000 colours to be displayed. AGA's "Paula" and "Gayle"
were unchanged but AGA "Denise" supported AGA "Agnus"'s new
screen modes. Unfortunately, even AGA "Paula" did not support
High Density floppy disk drives. (The Amiga 4000, though,
did support high density drives.) In order to use a high
density disk drive Amiga HD floppy drives spin at half the
rotational speed thus halving the data rate to "Paula".
Commodore Business Machines went bankrupt on 1994-04-29,
the German company Escom AG bought the rights to the Amiga
on 1995-04-21 and the Commodore Amiga became the Escom
Amiga. In April 1996 Escom were reported to be making the
Amiga range again but they too fell on hard times and
Gateway 2000 (now called Gateway) bought the Amiga brand
on 1997-05-15.
Gateway licensed the Amiga operating system to a German
hardware company called Phase 5 on 1998-03-09. The
following day, Phase 5 announced the introduction of a
four-processor PowerPC based Amiga clone called the
"pre\box". Since then, it has been announced that the
new operating system will be a version of QNX.
On 1998-06-25, a company called Access Innovations Ltd
announced plans (
http://www.micktinker.co.uk/aaplus.html) to
build a new Amiga chip set, the AA+, based partly on the AGA
chips but with new fully 32-bit functional core and 16-bit AGA
hardware register emulation for backward compatibility.
The new core promised improved memory access and video display
DMA.
By the end of 2000, Amiga development was under the control of
a [new?] company called Amiga, Inc.. As well as continuing
development of AmigaOS (version 3.9 released in December
2000), their "Digital Environment" is a virtual machine for
multiple platforms conforming to the ZICO specification.
As of 2000, it ran on MIPS, ARM, PPC, and x86
processors.
