= Atari_8-bit_family =

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= Atari_8-bit_family =
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Introduction
======================================================================
The Atari 8-bit computers, formally launched as the Atari Home
Computer System, are a series of home computers introduced by Atari,
Inc., in 1979 with the Atari 400 and Atari 800. The architecture is
designed around the 8-bit MOS Technology 6502 CPU and three custom
coprocessors which provide support for sprites, smooth
multidirectional scrolling, four channels of audio, and other
features. The graphics and sound are more advanced than most of its
contemporaries, and video games are a key part of the software
library. The 1980 first-person space combat simulator 'Star Raiders'
is considered the platform's killer app.

The Atari 800 was positioned as a high-end model and the 400 as more
affordable. The 400 has a pressure-sensitive, spillproof membrane
keyboard and initially shipped with a non-upgradable of RAM. The 800
has a conventional keyboard, a second cartridge slot, and allows easy
RAM upgrades to 48K. Both use identical 6502 CPUs at ( for PAL
versions) and coprocessors ANTIC, POKEY, and CTIA/GTIA. The
plug-and-play peripherals use the Atari SIO serial bus, and one of the
SIO developers eventually went on to co-patent USB (Universal Serial
Bus). The core architecture of the Atari 8-bit computers was reused in
the 1982 Atari 5200 game console, but games for the two systems are
incompatible.

The 400 and 800 were replaced by multiple computers with the same
technology and different presentation. The 1200XL was released in
early 1983 to supplant the 800. It was discontinued months later, but
the industrial design carried over to the 600XL and 800XL released
later the same year. After the company was sold and reestablished,
Atari Corporation released the 65XE (sold as the 800XE in some
European markets) and 130XE in 1985. The XL and XE are lighter in
construction, have two joystick ports instead of four, and Atari BASIC
is built-in. The 130XE has 128 KB of bank-switched RAM. In 1987, after
the Nintendo Entertainment System reignited the console market, Atari
Corporation packaged the 65XE as a game console, with an optional
keyboard, as the Atari XEGS. It is compatible with 8-bit computer
software and peripherals.

The 8-bit computers were sold both in computer stores and department
stores such as Sears using a demo to attract customers. Two million
Atari 8-bit computers were sold during its major production run
between late 1979 and mid-1985. The primary global competition came
when the similarly equipped Commodore 64 was introduced in August
1982. In 1992, Atari Corporation officially dropped all remaining
support for the 8-bit line.

History
======================================================================
Design of the "Home Computer System" started at Atari as soon as the
Atari Video Computer System was released in late 1977. While designing
the VCS in 1976, the engineering team from Atari Grass Valley Research
Center (originally Cyan Engineering) said the system would have a
three-year lifespan before becoming obsolete. They started planning
for a console that would be ready to replace it around 1979.

They developed essentially a greatly updated version of the VCS,
fixing its major limitations but sharing a similar design philosophy.
The newer design has better speed, graphics, and sound. Work on the
chips for the new system continued throughout 1978 and focused on a
much-improved video coprocessor known as the CTIA (the VCS version was
the TIA).

During the early development period, the home computer era began in
earnest with the TRS-80, PET, and Apple II--what 'Byte' magazine
dubbed the "1977 Trinity". Nolan Bushnell sold Atari to Warner
Communications for in 1976 to fund the launch of the VCS. In 1978,
Warner hired Ray Kassar as CEO of Atari. Kassar wanted the chipset
used in a home computer to challenge Apple, so it needed character
graphics, some form of expansion for peripherals, and run the
then-universal BASIC programming language.

Atari engineer Jay Miner created a display architecture for the Atari
8-bit computer consisting of two chips. The CTIA chip handles sprites
and background graphics, but to reduce load on the main CPU, loading
video registers and buffers is delegated to a dedicated
microprocessor, the Alphanumeric Television Interface Controller or
ANTIC. CTIA and ANTIC work together to produce a complete display,
with ANTIC fetching scan line data from a framebuffer and sprite
memory in RAM, plus character set bitmaps for character modes, and
feeding these to the CTIA. CTIA processes the sprite and playfield
data via its own color, sprite, and graphics registers to produce the
final color video output.

The resulting system was far in advance of anything then available on
the market. Commodore was developing a video driver at the time, but
Chuck Peddle, lead designer of the MOS Technology 6502 CPU used in the
VCS and the new machines, saw the Atari work during a visit to Grass
Valley. He realized the Commodore design would not be competitive but
he was under a strict non-disclosure agreement with Atari, and was
unable to tell anyone at Commodore to give up on their own design.
Peddle later commented that "the thing that Jay did, just kicked
everybody's butt."

Development
=============
Management identified two sweet spots for the new computers: a low-end
version known internally as "Candy", and a higher-end machine known as
"Colleen" (named after two Atari secretaries). Atari would market
Colleen as a computer and Candy as a game machine or hybrid game
console. Colleen includes user-accessible expansion slots for RAM and
ROM, two 8 KB ROM cartridge slots, RF and monitor output (including
two pins for separate luma and chroma suitable for superior S-Video
output) and a full keyboard. Candy was initially designed as a game
console, lacking a keyboard and input/output ports, although an
external keyboard was planned for joystick ports 3 and 4. At the time,
plans called for both to have a separate audio port supporting
cassette tapes as a storage medium.

A goal for the new systems was user-friendliness. One executive
stated, "Does the end user care about the architecture of the machine?
The answer is no. 'What will it do for me?' That's his major concern.
... why try to scare the consumer off by making it so he or she has to
have a double E or be a computer programmer to utilize the full
capabilities of a personal computer?" For example, cartridges were
expected to make the computers easier to use. To minimize handling of
bare circuit boards or chips, as is common with other systems of that
period, the computers were designed with enclosed modules for memory,
ROM cartridges, with keyed connectors to prevent them being plugged
into the wrong slot. The operating system boots automatically, loading
drivers from devices on the serial bus (SIO). The disk operating
system for managing floppy storage was menu-driven. When no software
is loaded, rather than leaving the user at a blank screen or machine
language monitor, the OS goes to the "Memo Pad" which is a built-in
full-screen editor without file storage support.

As the design process for the new machines continued, there were
questions about what the Candy should be. There was a running argument
about whether the keyboard would be external or built-in. By the
summer of 1978, education had become a focus for the new systems. The
Colleen design was largely complete by May 1978, but in early 1979 the
decision was made that Candy would also be a complete computer, but
intended for children. As such, it would feature a new keyboard
designed to be resistant to liquid spills.

Atari intended to port Microsoft BASIC to the machine as an 8 KB ROM
cartridge. However, the existing 6502 version from Microsoft was
around 7,900 bytes, leaving no room for extensions for graphics and
sound. The company contracted with local consulting firm Shepardson
Microsystems to complete the port. They recommended writing a new
version from scratch, resulting in Atari BASIC.

FCC issues
============
Televisions of the time normally had only one signal input, which was
the antenna connection on the back. For devices like a computer, the
video is generated and then sent to an RF modulator to convert it to
antenna-like output. The introduction of many game consoles during
this era had led to situations where poorly designed modulators would
generate so much signal as to cause interference with other nearby
televisions, even in neighboring houses. In response to complaints,
the Federal Communications Commission (FCC) introduced new testing
standards which are extremely exacting and difficult to meet.

Other systems avoided the problem by using built-in composite
monitors, such as the PET and TRS-80. The TRS-80 has a slightly
modified black and white television as a monitor. It was notorious for
causing interference, and production was canceled when the more
stringent FCC requirements came into effect on January 1, 1981. Apple
Computer left off the modulator and sold them under a third party
company as the Sup'R'Mod so they did not have to be tested.

In a July 1977 visit with the engineering staff, a Texas Instruments
salesman presented a new possibility in the form of an inexpensive
fiber-optic cable with built-in transceivers. During the meeting, Joe
Decuir proposed placing an RF modulator on one end, thereby completely
isolating any electrical signals so that the computer would have no RF
components. This would mean the computer would not have to meet the
FCC requirements, yet users could still attach a television simply by
plugging it in. His manager, Wade Tuma, later refused the idea saying
"The FCC would never let us get away with that stunt." Unknown to
Atari, TI used Decuir's idea. As Tuma had predicted, the FCC rejected
the design, delaying that machine's release. Texas Instruments shipped
early machines with a custom television as the testing process dragged
on.

To meet the off-the-shelf requirement while including internal TV
circuitry, both new machines were built around cast aluminum shields
forming a partial Faraday cage, with the various components screwed
down onto this internal framework. This resulted in a sturdy computer,
at the disadvantage of added manufacturing expense and complexity.

The FCC ruling also made it difficult to have any sizable holes in the
case, which would allow RF leakage. This eliminated expansion slots or
cards that communicated with the outside world via their own
connectors. Instead, Atari designed the Serial Input/Output (SIO)
computer bus, a system for daisy-chaining multiple, auto-configuring
devices to the computer through a single shielded connector. The
internal slots were reserved for ROM and RAM modules; they did not
have the control lines necessary for a fully functional expansion
card, nor room to route a cable outside the case to communicate with
external devices.

400 and 800 release
=====================
After Atari announced its intent to enter the home computer market in
December 1978, the Atari 400 and Atari 800 were presented at the
Winter CES in January 1979 and shipped in November 1979.

The names originally referred to the amount of memory: 4 KB RAM in the
400 and 8 KB in the 800. By the time they were released, RAM prices
had started to fall, so the machines were both released with 8 KB,
using 4kx1 DRAMs. The user-installable RAM modules in the 800
initially had plastic casings but this caused overheating issues, so
the casings were removed. Later, the expansion cover was held down
with screws instead of the easier-to-open plastic latches. The
computers eventually shipped with maxed-out RAM: 16k and 48k,
respectively, using 16kx1 DRAMs.

Both models have four joystick ports, permitting four simultaneous
players, but only a few games (such as 'M.U.L.E.') use them all.
Paddle controllers are wired in pairs, and 'Super Breakout' supports
eight players. The Atari 400, with a membrane keyboard and single
internal ROM slot, outsold the Atari 800 by a 2-to-1 margin. Only one
cartridge for the 800's right slot was produced by March 1983, and
later machines in the series have only one slot.

'Creative Computing' mentioned the Atari machines in an April 1979
overview of the CES show. Calling Atari "the videogame people", it
stated they came with "some fantastic educational, entertainment and
home applications software". In an August 1979 interview Atari's Peter
Rosenthal suggested that demand might be low until the 1980-81 time
frame, when he predicted about one million home computers being sold.
The April 1980 issue compared the machines with the Commodore PET,
focused mostly on the BASIC dialects. Ted Nelson reviewed the computer
in the magazine in June 1980, calling it "an extraordinary graphics
box". Describing his and a friend's "shouting and cheering and
clapping" during a demo of 'Star Raiders', Nelson wrote that he was so
impressed that "I've been in computer graphics for twenty years, and I
lay awake night after night trying to understand how the Atari machine
did what it did". He described the machine as "something else" but
criticized the company for a lack of developer documentation. He
concluded by stating "The Atari is like the human body - a terrific
machine, but (a) they won't give you access to the documentation, and
(b) I'd sure like to meet the guy that designed it". 'Kilobaud
Microcomputing' wrote in September 1980 that the Atari 800 "looks
deceptively like a video game machine, [but had] the strongest and
tightest chassis I have seen since Raquel Welch. It weighs about ten
pounds ... The large amount of engineering and design in the physical
part of the system is evident". The reviewer praised the documentation
as "show[ing] the way manuals should be done", and the "excellent
'feel of the keyboard. 'InfoWorld' favorably reviewed the 800's
performance, graphics, and ROM cartridges, but disliked the
documentation and cautioned that the unusual right Shift key location
might make the computer "unsuitable for serious word processing".
There is an "Atari key" between the and shift, whereas a typical
keyboard would extend the shift key into this area. Noting that the
amount of software and hardware available for the computer "is no
match for that of the Apple II or the TRS-80", the magazine concluded
that the 800 "is an impressive machine that has not yet reached its
full computing potential".

400/800 evolution
===================
In October-November 1981, Atari began shipping the 400 and 800 with
the GTIA chip instead of the CTIA chip used since launch. Existing
computers could be upgraded. GTIA adds three graphics modes with more
colors, but at a low horizontal resolution (). Some later software
relies on GTIA modes such as 'Koronis Rift' and 'Space Lobsters'.

Circa 1982, the base memory in both models increased: from 8K to 16K
for the Atari 400 and from 16K to 48K for the Atari 800.

Sweet/Liz project
===================
Though planning an extensive advertising campaign for 1980, Atari
found difficult competition from Commodore, Apple, and Tandy. By
mid-1981, it had reportedly lost $10 million on sales of $10-13
million from more than 50,000 computers.

In 1982, Atari started the Sweet 8 (also called Liz NY) and Sweet 16
projects to create new machines that were easier to build and less
costly to produce. Atari ordered a custom 6502 with logic to disable
the clock signal, called HALT, which ANTIC uses to shut off the CPU to
access the data/address bus. This "SALLY" CPU was incorporated into
late-production 400 and 800 models, all XL/XE models, and the Atari
5200 and Atari 7800 consoles.

Mirroring the 400/800, two systems were planned, the 1000 with 16 KB
and the 1000X with 64 KB, each expandable via a Parallel Bus Interface
slot on the back of the machine.

1200XL
========
The original Sweet 8/16 plans were dropped and only one machine using
the new design was released. Announced at a New York City press
conference on December 13, 1982, the 1200XL was presented at the
Winter CES on January 6-9, 1983. It shipped in March 1983 with 64 KB
of RAM, built-in self test, a redesigned keyboard (with four function
keys and a HELP key), and redesigned cable port layout. The number of
joystick ports was reduced from 4 to 2. There is no PAL version of the
1200XL.

Announced at a retail price of $1000, the 1200XL was released at .
This is $100 less than the announced price of the Atari 800 at its
release in 1979, but by this time the 800 was priced much lower.

The system uses the SIO port again instead of the Parallel Bus
Interface. The +12V pin in the SIO port is not connected, which
prevents a few devices from working. The +12V was typically used to
power RS-232 devices, which now required an external power source. An
improved video circuit provides more chroma for a more colorful image,
but the chroma line is not connected to the monitor port, the only
place that could make use of it. The operating system has
compatibility problems with some older software.

The 1200XL was discontinued in June 1983.

'Compute!' stated in an early 1983 editorial that the 1200XL was too
expensive; John J. Anderson of 'Creative Computing' agreed. Bill
Wilkinson, author of Atari BASIC, co-founder of Optimized Systems
Software, and columnist for 'Compute!', criticized the computer's
features and price. He wrote that the 1200XL was a "terrific bargain"
if sold for less than $450, but that if it cost more than the 800,
"buy an 800 quick!"

600XL and 800XL
=================
In May 1981, the Atari 800's price was , but by mid-1983, because of
price wars in the industry, it was and the 400 was under , down from
under in 1982. The 1200XL was a flop, and the earlier machines were
too expensive to produce to be able to compete at the rapidly falling
price points.

A new lineup was announced at the 1983 Summer Consumer Electronics
Show, closely following the original Sweet concepts. The 600XL is
essentially the Liz NY model and the spiritual successor of the 400,
and the 800XL would replace both the 800 and 1200XL. The machines
follow the styling of the 1200XL but are smaller from back to front,
and the 600XL is more so.

Atari had difficulty in transitioning manufacturing to Asia after
closing its US factory in 1983. Originally intended to replace the
1200XL in mid-1983, the new models did not arrive until late that
year. Although the 600XL/800XL were well positioned in terms of price
and features, during the critical Christmas season they were available
only in small numbers while the Commodore 64 was widely available.
Brian Moriarty stated in 'ANALOG Computing' that Atari "fail[ed] to
keep up with Christmas orders for the 600 and 800XLs", reporting that
as of late November 1983 the 800XL had not appeared in Massachusetts
stores while 600XL "quantities are so limited that it's almost
impossible to obtain".

After losing in the first nine months of the year, Atari that month
announced that prices would rise in January, stating that it "has no
intention of participating in these suicidal price wars." The 600XL
and 800XL's prices in early 1984 were $50 higher than for the VIC-20
and Commodore 64.

'ANALOG Computing', writing about the 600XL in January 1984, stated
that "the Commodore 64 and Tandy CoCo look like toys by comparison."
The magazine approved of its not using the 1200XL's keyboard layout,
and predicted that the XL's parallel bus "actually makes the 600
'more' expandable than a 400 or 800." While disapproving of the use of
an operating system closer to the 1200XL's than the 400 and 800's, and
the "inadequate and frankly disappointing" documentation, 'ANALOG'
concluded that "our first impression ... is mixed but mostly
optimistic." The magazine warned, however, that because of "Atari's
sluggish marketing", unless existing customers persuaded others to buy
the XL models, "we'll all end up marching to the beat of a drummer
whose initials are IBM." By March 1984, all of Atari's computer models
were produced in Hong Kong by the Atari-Wong joint venture.

Unreleased XL models
======================
The high-end 1400XL and 1450XLD were announced alongside the 600XL and
800XL. They added a built-in 300 baud modem and a voice synthesizer,
and the 1450XLD has a built-in double-sided floppy disk drive in an
enlarged case, with a slot for a second drive. Atari BASIC is built
into the ROM and the PBI at the back for external expansion.

The 1400XL and the 1450XLD had their delivery dates pushed back, and
in the end, the 1400XL was canceled outright, and the 1450XLD so
delayed that it would never ship. Other prototypes which never reached
market include the 1600XL, 1650XLD, and 1850XLD. The 1600XL was to
have been a dual-processor model capable of running 6502 and 80186
code, and the 1650XLD is a similar machine in the 1450XLD case. These
were canceled when James J. Morgan became CEO and wanted Atari to
return to its video game roots. The 1850XLD was to have been based on
the Lorraine chipset which became the Amiga.

Tramiel takeover, declining market
====================================
Commodore founder Jack Tramiel resigned in January 1984 and in July,
he purchased the Atari consumer division from Warner for an extremely
low price. No cash was required, and instead Warner had the right to
purchase in long-term notes and warrants, and Tramiel had an option
to buy up to in Warner stock. When Tramiel took over, the high-end XL
models were canceled and the low-end XLs were redesigned into the XE
series. Nearly all research, design, and prototype projects were
canceled, including the Amiga-based 1850XLD. Tramiel focused on
developing the 68000-based Atari ST computer line and recruiting
former Commodore engineers to work on it.

Atari sold about 700,000 computers in 1984 compared to Commodore's two
million. As his new company prepared to ship the Atari ST in 1985,
Tramiel stated that sales of Atari 8-bit computers were "very, very
slow". They were never an important part of Atari's business compared
to video games, and it is possible that the 8-bit line was never
profitable for the company though almost 1.5 million computers had
been sold by early 1986.

By that year, the Atari software market was decreasing in size.
'Antic' magazine stated in May 1985 that it had received many letters
complaining that software companies were ignoring the Atari market,
and urged readers to contact the companies' leaders. "The Atari 800
computer has been in existence since 1979. Six years is a pretty long
time for a computer to last. Unfortunately, its age is starting to
show", 'ANALOG Computing' wrote in February 1986. The magazine stated
that while its software library was comparable in size to that of
other computers, "now--and even more so in the future--there is going
to be less software being made for the Atari 8-bit computers", warning
that 1985 only saw a "trickle" of major new titles and that 1986 "will
be even leaner".

'Computer Gaming World' that month stated "games don't come out for
the Atari first anymore". In April, the magazine published a survey of
ten game publishers which found that they planned to release 19 Atari
games in 1986, compared to 43 for Commodore 64, 48 for Apple II, 31
for IBM PC, 20 for Atari ST, and 24 for Amiga. Companies stated that
one reason for not publishing for Atari was the unusually high amount
of software piracy on the computer, partly caused by the Happy Drive.
The magazine warned later that year, "Is this the end for Atari 800
games? It certainly looks like it might be from where I write". In
1987, MicroProse confirmed that it would not release 'Gunship' for the
Atari 8-bits, stating that the market was too small.

XE series
===========
The 65XE and 130XE (XE stands for XL-Compatible Eight-bit) were
announced in 1985 at the same time as the Atari 520ST, and they
visually resemble the ST. The 65XE has 64 KB of RAM and is
functionally equivalent to the 800XL minus the PBI connection. The
130XE has 128 KB of memory, accessible through bank switching. The
additional 64K can be used as a RAM drive.

The 130XE includes the Enhanced Cartridge Interface (ECI), which is
almost compatible with the Parallel Bus Interface, but physically
smaller and located next to the standard 400 and 800 compatible
cartridge slot. It provides only those signals that do not exist in
the latter. ECI peripherals were expected to plug into both the
standard Cartridge Interface and the ECI port. Later revisions of the
65XE contain the ECI port.

The 65XE was sold as the 800XE in Germany and Czechoslovakia to ride
on the popularity of the 800XL in those markets. All 800XE units
contain the ECI port.

XE Game System
================
The Atari XEGS (XE Game System) was launched in 1987. A repackaged
65XE with a removable keyboard, it boots to the 1981 port of 'Missile
Command' instead of BASIC if the keyboard is disconnected.

Design
======================================================================
The Atari machines consist of a 6502 as the main processor, a
combination of ANTIC and GTIA chips to provide graphics, and the POKEY
chip to handle sound and serial input/output. These support chips are
controlled via a series of registers that can be user-controlled via
memory load/store instructions running on the 6502. For example, the
GTIA uses a series of registers to select colors for the screen; these
colors can be changed by inserting the correct values into its
registers, which are mapped into the address space that is visible to
the 6502. Some of the coprocessors use data stored in RAM, such as
ANTIC's display buffer and display list, and GTIA's Player/Missile
(sprite) information.

The custom hardware features enable the computers to perform many
functions directly in hardware, such as smooth background scrolling,
that would need to be done in software in most other computers.
Graphics and sound demos were part of Atari's earliest developer
information and used as marketing materials with computers running
in-store demos.

ANTIC
=======
ANTIC is a microprocessor which processes a sequence of instructions
known as a display list. An instruction adds one row of the specified
graphics mode to the display. Each mode varies based on whether it
represents text or a bitmap, the resolution and number of colors, and
its vertical height in scan lines. An instruction also indicates if it
contains an interrupt, if fine scrolling is enabled, and optionally
where to fetch the display data from memory.

Since each row can be specified individually, the programmer can
create displays containing different text or bitmapped graphics modes
on one screen, where the data can be fetched from arbitrary,
non-sequential memory addresses.

ANTIC reads this display list and the display data using DMA (Direct
Memory Access), then translates the result into a pixel data stream
representing the playfield text and graphics. This stream then passes
to GTIA which applies the playfield colors and incorporates
Player/Missile graphics (sprites) for final output to a TV or
composite monitor. Once the display list is set up, the display is
generated without any CPU intervention.

There are 15 character and bitmap modes. In low-resolution modes, 2 or
4 colors per display line can be set. In high-resolution mode, one
color can be set per line, but the luminance values of the foreground
and background can be adjusted. High resolution bitmap mode (320x192
graphics) produces NTSC composite artifact colors; these colors do not
occur on PAL machines.

For text modes, the character set data is pointed to by a register. It
defaults to an address in ROM, but if pointed to RAM then a programmer
can create custom characters. Depending on the text mode, this data
can be on any 1K or 512 byte boundary. Additional registers flip all
characters upside down and toggle inverse video.

The ANTIC chip allows a variety of Playfield modes and widths, and the
original Atari Operating System included with the Atari 800/400
computers provides easy access to a subset of these graphics modes.
These are exposed to users through Atari BASIC via the "GRAPHICS"
command and to some other languages via similar system calls. The
later version of the OS used in the XL/XE computers added support for
most of these "missing" graphics modes.

ANTIC text modes support soft, redefineable character sets. ANTIC has
four different methods of glyph rendering related to the text modes:
Normal, Descenders, Single color character matrix, and Multiple colors
per character matrix.

The ANTIC chip uses a display list and other settings to create these
modes. Any graphics mode in the default CTIA/GTIA color interpretation
can be freely mixed without CPU intervention by changing instructions
in the display list.

The actual ANTIC screen geometry is not fixed. The hardware can be
directed to display a narrow Playfield (128 color clocks/256 hi-res
pixels wide), the normal width Playfield (160 color clocks/320 hi-res
pixels wide), and a wide, overscan Playfield (192 color clocks/384
hi-res pixels wide) by setting a register value. The operating
system's default height for creating graphics modes is 192 scan lines,
and ANTIC can display vertical overscan up to 240 TV scan lines tall
by creating a custom display list.

The display list capabilities provide horizontal and vertical coarse
scrolling requiring minimal CPU direction. Furthermore, the ANTIC
hardware supports horizontal and vertical fine scrolling--shifting the
display of screen data incrementally by single pixels (color clocks)
horizontally and single scan lines vertically.

The system CPU clock and video hardware are synchronized to one-half
the NTSC clock frequency. Consequently, the pixel output of all
display modes is based on the size of the NTSC color clock which is
the minimum size needed to guarantee correct and consistent color
regardless of the pixel location on the screen. The fundamental
accuracy of the pixel color output allows horizontal fine scrolling
without color "strobing"--unsightly hue changes in pixels based on
horizontal position caused when signal timing does not provide the
TV/monitor hardware adequate time to reach the correct color.

CTIA/GTIA
===========
The Color Television Interface Adaptor (CTIA) is the graphics chip
originally used in the Atari 400 and 800. It is the successor to the
TIA chip of the 1977 Atari VCS. According to Joe Decuir, George McLeod
designed the CTIA in 1977. It was replaced with the Graphic Television
Interface Adaptor (GTIA) in later revisions of the 400 and 800 and all
later 8-bit models. GTIA, also designed by McLeod, adds three new
playfield graphics modes to ANTIC which enable more colors.

The CTIA/GTIA receives Playfield graphics information from ANTIC and
applies colors to the pixels from a 128 or 256 color palette depending
on the color interpretation mode in effect. CTIA/GTIA controls
Player/Missile Graphics (sprites) including collision detection
between players, missiles, and the playfield; display priority for
objects; and color/luminance control of all displayed objects.
CTIA/GTIA outputs separate digital luminance and chroma signals, which
are mixed to form an analog composite video signal.

CTIA/GTIA reads the joystick triggers and the Option, Select and Start
keys, and controls the keyboard speaker in the Atari 400 and 800. In
later computer models the audio output for the keyboard speaker is
mixed with the audio out for transmission to the TV/video monitor.

POKEY
=======
POKEY is a custom chip used for reading the keyboard, generating sound
and serial communications (in conjunction with the Peripheral
Interface Adapter chip) commands and IRQs, plus controlling the 4
joystick movements on the 400 and 800 models, and later RAM banks or
ROM (OS/BASIC/Self-test) enables for XL/XE lines. It provides timers,
a random number generator for generating acoustic noise and random
numbers, and maskable interrupts. POKEY has four semi-independent
audio channels, each with its own frequency, noise and volume control.
Each 8-bit channel has its own audio control register which select the
noise content and volume. For higher sound frequency resolution
(quality), two of the audio channels can be combined for more accurate
sound (frequency can be defined with 16-bit value instead of usual
8-bit). The name POKEY comes from the words "POtentiometer" and
"KEYboard", which are two of the I/O devices that POKEY interfaces
with (the potentiometer is the mechanism used by the paddle). The
POKEY chip--and its dual- and quad-core versions--was used in many
Atari coin-op arcade machines of the 1980s, including 'Centipede' and
'Millipede', 'Missile Command', 'Asteroids Deluxe', 'Major Havoc', and
'Return of the Jedi'.

Models
========
Atari, Inc. shipped three updated versions of the 400/800 using the
same chipset and with a different case aesthetic: the short-lived
1200XL, then the 600XL and 800XL. Numerous other, wide-ranging
projects to develop successors to the 8-bit line were cancelled. After
the re-establishment of Atari as Atari Corporation, three more systems
were released using largely the same technology as earlier machines:
the 65XE and 128 KB 130XE in 1985, and finally the game console
inspired Atari XEGS in 1987.

* 400 and 800 (1979) - original machines in beige cases. Both have 4
joystick ports below the keyboard and a cartridge slot covered by a
door on the top of the machine. The 400 has a membrane keyboard. The
800 has full-travel keys, a second, rarely used, cartridge slot, and
monitor output. Both have expandable memory (up to 48 KB); the RAM
slots are easily accessible in the 800. Later PAL versions have the
6502C processor.
* 1200XL (1983) - new aluminum and smoked plastic case. Includes 64 KB
of RAM, two joystick ports, a Help key, and four function keys. Some
older software was incompatible with the new OS. Starting with the
1200XL, the single cartridge slot is on the side of the case, and
there are only 2 joystick ports.
* 600XL and 800XL (1983) - the 600XL has 16 KB of memory and PAL
versions have a monitor port. The 800XL has 64 KB and monitor output.
Both have built-in BASIC and a Parallel Bus Interface (PBI) expansion
port. The last produced PAL units contain the Atari FREDDIE chip and
Atari BASIC revision C.
* 65XE and 130XE (1985) - the 65XE has 64 KB of RAM. The 130XE has 128
KB of bank-switched RAM and an Enhanced Cartridge Interface (ECI)
instead of a PBI. The first revisions of the 65XE have no ECI or PBI,
and the later ones contain the ECI. The 65XE was relabelled as 800XE
due to the local popularity of the 800XL, and was mostly sold in
Central Europe.
* XE Game System (1987) - a 65XE styled as a game console. The basic
version of the system shipped without the detachable keyboard. With
the keyboard it operates just like other Atari 8-bit computer models.
The cartridge slot is on the top, like other consoles.

Production timeline
=====================
ImageSize = width:800 height:auto barincrement:25
PlotArea = left:115 bottom:110 top:20 right:10
Alignbars = justify
DateFormat= mm/dd/yyyy
Period = from:01/01/1979 till:06/30/1992
TimeAxis = orientation:horizontal format:yyyy
Legend = orientation:vertical position:bottom columns:4
ScaleMajor= increment:1 start:1979
ScaleMinor= increment:2 start:1979

Colors =
id:400_Line value:green legend:400_&_800_Line
id:XE_Line value:blue legend:XE_Line
id:XL_Line value:orange legend:XL_Line
id:Lines value:black
legend:Vertical_lines_are_Product_Announcements
id:XEGS value:lavender legend:XEGS

LineData =
at:01/05/1979 color:green layer:back
at:12/13/1982 color:orange layer:back
at:06/10/1983 color:orange layer:back
at:01/05/1985 color:blue layer:back
at:01/05/1987 color:lavender layer:back
at:01/01/1992 color:black layer:back

BarData =
bar:400 text:"400 & 800"
bar:5200 text:"5200"
bar:1200XL text:"1200XL"
bar:600XL text:"600XL"
bar:800XL text:"800XL"
bar:65XE text:"65XE"
bar:130XE text:"130XE"
bar:800XE text:"800XE"
bar:XEGS text:"XEGS"

PlotData =
width:10 textcolor:black align:left anchor:from shift:(10,-4)
bar:400 from:06/05/1979 till:05/01/1983 color:400_Line
bar:5200 from:11/01/1982 till:05/21/1984 color:400_Line
bar:1200XL from:03/01/1983 till:07/01/1983 color:XL_Line
bar:600XL from:07/01/1983 till:07/15/1984 color:XL_Line
bar:800XL from:07/01/1983 till:02/14/1985 color:XL_Line
bar:65XE from:05/05/1985 till:06/02/1991 color:XE_Line
bar:130XE from:01/05/1985 till:02/02/1991 color:XE_Line
bar:800XE from:05/05/1987 till:01/01/1992 color:XE_Line
bar:XEGS from:08/05/1987 till:02/14/1991 color:XEGS

width:3 textcolor:black align:left anchor:from shift:(10,-4)

The production timeline is from 1979 to 1987.

Prototypes and vaporware
==========================
* 1400XL: similar to the 1200XL but with a PBI, FREDDIE chip, built-in
modem and a Votrax SC-01 speech synthesis chip. Cancelled.
* 1450XLD: a 1400XL with built-in ″ disk drive and expansion bay for a
second ″ disk drive. Code named 'Dynasty'. Made it to pre-production,
but was abandoned by Tramiel.
* 1600XL: codenamed 'Shakti', this was dual-processor system with 6502
and 80186 processors and two built-in ″ floppy disk drives.
* 1850XL: codenamed 'Mickey', this was to use the "Lorraine" (aka
"Amiga") custom graphics chips
* 65XEM: 65XE with AMY sound synthesis chip. Cancelled.
* 65XEP: "portable" 65XE with " disk drive, 5" green CRT and battery
pack.

Peripherals
======================================================================
During the lifetime of the 8-bit series, Atari released a large number
of peripherals including cassette tape drives, 5.25-inch floppy
drives, printers, modems, a touch tablet, and an 80-column display
module.

Atari's peripherals use the proprietary Atari SIO port, which allows
them to be daisy chained together. A primary goal of the Atari
computer design was user-friendliness which was assisted by the SIO
bus. Since only one kind of connector plug is used for all devices the
Atari computer was easy for novice users to expand. Atari SIO devices
use an early form of plug-n-play. Peripherals on the bus have their
own IDs, and can deliver downloadable drivers to the Atari computer
during the boot process. The additional electronics in these
peripherals made them cost more than the equivalent "dumb" devices
used by other systems of the era.

Software
======================================================================
Atari did not initially disclose technical information for its
computers, except to software developers who agreed to keep it secret,
possibly to increase its own software sales. Cartridge software was so
rare at first that 'InfoWorld' joked in 1980 that Atari owners might
have considered turning the slot "into a fancy ashtray". The magazine
advised them to "clear out those cobwebs" for Atari's 'Star Raiders',
which became the platform's killer app, akin to VisiCalc for the Apple
II in its ability to persuade customers to buy the computer.

Chris Crawford and others at Atari published detailed technical
information in 'De Re Atari'. In 1982, Atari published both the 'Atari
Home Computer System Hardware Manual' and an annotated source listing
of the operating system. These resources resulted in many books and
articles about programming the computer's custom hardware.

Because of graphics superior to those of the Apple II and Atari's
home-oriented marketing, games dominated its software library. A 1984
compendium of reviews used 198 pages for games compared to 167 for all
others.

Built-in operating system
===========================
The Atari 8-bit computers have an operating system built into the ROM.
The Atari 400 and 800 have two versions:
*OS Rev. A - 10 KB ROM (3 chips) early machines
*OS Rev. B - 10 KB ROM (3 chips) most common

The XL/XE all have OS revisions, which created compatibility issues
with certain software. Atari responded with the Translator Disk, a
floppy disk which loads the older 400 and 800 Rev. 'B' or Rev. 'A' OS
into the XL/XE computers.
*OS Rev. 10 - 16 KB ROM (2 chips) for 1200XL Rev A
*OS Rev. 11 - 16 KB ROM (2 chips) for 1200XL Rev B (bug fixes)
*OS Rev. 1 - 16 KB ROM for 600XL
*OS Rev. 2 - 16 KB ROM for 800XL
*OS Rev. 3 - 16 KB ROM for 800XE/130XE
*OS Rev. 4 - 32 KB ROM (16 KB OS + 8 KB BASIC + 8 KB Missile Command)
for XEGS

The XL/XE models that followed the 1200XL also have the Atari BASIC
ROM built-in, which can be disabled at startup by holding down the
silver OPTION key. Originally this was revision B, which has some
serious bugs. Later models have revision C.

Disk Operating System
=======================
The standard Atari OS only contains low-level routines for accessing
floppy disk drives. An extra layer, a disk operating system, is
required to assist in organizing file system-level disk access. Atari
DOS has to be booted from floppy disk at every power-on or reset.
Atari DOS is entirely menu-driven.

*DOS 1.0
*DOS 2.0S - Improved over DOS 1.0; became the standard for the 810
disk drive.
*DOS 3.0 - Came with 1050 drive. Uses a different disk format which is
incompatible with DOS 2.0, making it unpopular.
*DOS 2.5 - Replaced DOS 3.0 with later 1050s. Functionally identical
to DOS 2.0S, but able to read and write enhanced density disks.
*DOS XE - Designed for the Atari XF551 double-density drive.

Third-party replacement DOSes were also available.

Legacy
======================================================================
At the beginning of 1992, Atari Corporation officially dropped all
remaining support for all the 8-bit computers. In 2006, Curt Vendel,
who designed the Atari Flashback, claimed that Atari released the
8-bit chipset into the public domain. There is agreement in the
community that Atari authorized the distribution of the Atari 800's
ROM with the Xformer 2.5 emulator, which makes the ROM legally
available today as freeware.

On March 29, 2024, Atari SA and Retro Games Ltd, via the distributor
Plaion, released the Atari 400 Mini, at a cost of £99.99 (€119.99 /
$119.99). It is a half-sized scale-model microconsole emulation of the
Atari 400, preloaded with 25 games. It comes with an updated Atari
CX40 joystick with additional buttons.

External links
======================================================================
*
[http://www.atarimuseum.com/computers/8BITS/400800/peripherals/index.html
Atari 400/800 Peripherals]
*
[https://www.gamedeveloper.com/game-platforms/a-history-of-gaming-platforms-atari-8-bit-computers
"A History of Gaming Platforms: Atari 8-bit Computers"] at Gamasutra
*
[http://www.atarimuseum.com/computers/8BITS/XL/XL-Pages/xl-range-main.htm
Atari XL Series Systems & Prototypes]
* [http://www.xmission.com/~trevin/atari/atari.html Technical chipset
information]

License
=========
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License URL: http://creativecommons.org/licenses/by-sa/3.0/
Original Article: http://en.wikipedia.org/wiki/Atari_8-bit_family