Atari 400 upgrades

Upgrades an Atari 1050 disk drive for divisor-6 high speed, 180 KB per side, and flashable firmware slots.

For this system (bus/interface): This modifies an external Atari 1050 SIO drive rather than the computer. Confirm normal drive and SIO operation before installation and use host software that supports the selected high-speed and density modes.

Lotharek marks 1050E discontinued. The seller calls installation solderless, but it still requires opening the drive, removing three chips, moving the 6507 CPU, and preserving socket orientation. Confirm that a used kit is complete, that all original chips and sockets are healthy, and that suitable 1050E firmware and host software are available.

Replaces the Atari 400's internal RAM board with either 48 KB or 1056 KB of modern memory.

For this system (exact model): Both variants are designed specifically for the Atari 400. Choose 48 KB for a conventional base-memory upgrade or 1056 KB for 48 KB of base RAM plus 1008 KB of Axlon-compatible banked RAM; both require the four documented motherboard jumpers.

Both product pages reported five boards in stock on 2026-07-27. Either installation requires disassembling the computer and soldering four jumper wires beneath the main board. A machine previously fitted with Atari's 48K RAM Expansion Kit may already have those jumpers. The 1056K board does not require the plastic-housing modification described in the older Atari kit instructions.

Retains the original POKEY while adding FPGA stereo POKEYs, Covox channels, digital mixing, and a high-rate stereo DAC.

For this system (stated family): The seller states that ACID STEREO supports all Atari 8-bit systems. The public page illustrates an 800XL full-install path rather than a 400-specific route, so confirm socket clearance, address signals, and audio pickup points for this motherboard.

The product exposed a login-or-register-to-buy path on 2026-07-27. It requires a working original POKEY and can be installed in stages: basic stereo output, a second POKEY through an A4 connection, Covox through D6xx or D7xx decoding, and full internal-audio mixing. The approximately 1 mm PCB intentionally leaves pin 31 unconnected; verify that it remains isolated from the motherboard. Only the basic stage uses a single address jumper, while the expanded functions require additional signal and audio wiring.

Period SIO floppy drive adds double-sided, double-density 5.25-inch storage and faster double-density transfers to Atari 8-bit computers.

For this system (exact model): Atari's XF551 manual explicitly covers DOS use on the Atari 400. It requires a BASIC cartridge when BASIC is wanted, plus the drive's power adapter and an SIO cable.

Find a complete used drive with the correct AC adapter and SIO cable. The bundled DOS 2.5 supports single and enhanced density but not the XF551's full double-sided, double-density capacity; use DOS XE or compatible third-party software for that mode. Most drives use a Mitsumi mechanism with a rectangular activity LED, while later Chinon examples have a round LED and stricter flippy-disk limitations. The 300 RPM mechanism can also conflict with a small amount of speed-sensitive copy protection.

Provides blank flash cartridges and a USB programmer for building reusable Atari 8-bit multicarts.

For this system (stated family): Atarimax explicitly describes the Maxflash system for Atari 400, 800, XL, and XE computers. The cartridge is used in the Atari while the separate USB programmer and Maxflash Studio prepare its contents on a modern computer.

The official page showed the cartridges and USB programmer in stock on 2026-07-25. These are blank programmable products and do not include commercial ROM images. Unplug the programmer before attaching a cartridge, verify label-side-up orientation, and connect directly to the PC rather than through a USB hub for first-time use. Backwards insertion can damage both the cartridge and programmer.

Connects Atari 8-bit SIO computers and disk drives to a modern host for peripheral emulation and disk transfer.

For this system (bus/interface): Atarimax describes the interface for all Atari 8-bit computers, and it connects through SIO. USB versions are intended for Atarimax APE on Windows, while the RS-232 version can use SIO2PC software on several host operating systems. Confirm the required SIO cable and chain position.

The official page showed USB and RS-232 ordering options on 2026-07-25. Select the interface and connector arrangement for the intended host software and SIO chain. An Atari SIO cable and the computer or disk-drive hardware needed by the chosen workflow are not included. The USB setup documentation is dated and lists Windows 95 through Windows 7, so confirm current host support rather than assuming modern Windows compatibility.

Adds Wi-Fi networking and platform-specific peripheral emulation to several vintage computer families.

For this system (stated family): The official project publishes a current 400/800 owner's guide and presents 400/800-style Atari SIO hardware. Use an Atari SIO version, then confirm its enclosure, cable, power path, and firmware rather than assuming another platform's FujiNet hardware applies.

JCM showed 16 Apple II base units in stock on 2026-07-24. On 2026-07-27 Lotharek offered its assembled Atari Professional version both alone and with a dedicated SIO cable. It normally takes operating power from Atari SIO and uses USB-C for firmware flashing, although the page separately calls USB-C an optional power source for the 1200XL. The project also lists other small-batch vendors and open design files. Stock, enclosure, connection, power, and required interface hardware vary by computer.

Upgrades an Atari 1050 disk drive with true double density, faster backup operations, and protected-disk support.

For this system (bus/interface): This upgrades an external Atari 1050 SIO disk drive rather than the computer itself. The guide covers all Atari 1050 drives and explicitly excludes other drive models; verify that the 1050 and the rest of the SIO chain work normally before installation.

The 5cfab stand-alone Happy Warp 1050 v7.1 reproduction reported two boards in stock on 2026-07-27; Atarimax still provided a conditional add-on route on 2026-07-25. The 5cfab board includes its CPU and needs no soldering, but installation still requires opening the drive and carefully replacing internal hardware. Align the board's crystal with its clearance hole. The Atarimax guide also warns about static, alignment, and orientation.

Adds an SIO-connected General MIDI file synthesizer with external stereo output and Atari audio mixing.

For this system (bus/interface): The seller describes an Atari 8-bit SIO connection but does not provide a model list. Confirm the required Atari software and whether monitor-audio mixing works on the 400 before purchase; external stereo output is separately available.

The product exposed a login-or-register-to-buy path on 2026-07-27. It is a MIDI-file synthesizer, not the MyTek MIDI input/output interface already in the catalog. The public page and human review provide no written player-software, file-workflow, or model-specific SIO-audio instructions. Treat the external stereo output as the documented playback path and confirm software availability before purchase.

Replaces a failed or missing Atari POKEY with an updateable FPGA module in the original DIP-40 socket.

For this system (exact model): The seller explicitly names the Atari 400. Confirm that its POKEY is in a standard DIP-40 socket, orient the replacement correctly, and retain the compatibility warning for software that relies on undocumented analog or electrical behavior.

The product exposed a login-or-register-to-buy path on 2026-07-27. Installation is solderless only when the computer already has a compatible DIP-40 POKEY socket. This is a functional FPGA replacement, not a transistor-level NMOS clone; the seller warns that software depending on undocumented analog behavior or exact electrical characteristics may behave differently. The built-in USB port allows future firmware updates.

Connects Atari SIO computers to a modern USB host, with 10502PC variants that can also image disks through a physical Atari drive.

For this system (bus/interface): The seller requires any Atari 8-bit computer with a free SIO port, and the SIO2PC manual explicitly distinguishes the 400/800 BASIC-cartridge workflow. Select DSR or CTS handshaking for the exact adapter, and use a 10502PC variant when imaging disks through a physical Atari drive.

The basic SIO2PC USB, 10502PC Revision 2, and USB-C Revision 3 pages all exposed login-or-register-to-buy paths on 2026-07-27. Host emulation requires a modern computer, FTDI serial drivers where needed, and software such as RespeQt or AspeQt. The basic interface's manual uses DSR handshaking, while the 10502PC pages specify CTS for SIO2PC mode. Physical-drive imaging requires a 10502PC variant, ALibPC, and the documented FTDI setup; launching ALibPC changes the adapter to 10502PC mode, and unplugging and reconnecting USB restores its default SIO2PC mode.

Connects a PS/2 mouse to Commodore, Amiga, Atari ST, and Atari 8-bit computers with host-specific mouse, joystick, paddle, and tablet modes.

For this system (stated family): The Atari 8-bit mode defaults to the Atari ST mouse protocol and also offers CX22 trackball, Amiga mouse, joystick, paddle, and Koala Pad modes. Software must support the selected protocol.

The official shop listed immediate delivery from EUR 34.07 on 2026-07-30. Protovision listed five units from EUR 38, with the slim connector costing EUR 3 more. The slim version fits every supported computer; the wider screw-in version has documented clearance exclusions including the Amiga 600 and Atari 1200XL. A USB mouse works only if the mouse itself supports the PS/2 protocol through a passive adapter.

Converts a PS/2 mouse into Atari 8-bit or Atari ST quadrature mouse signals.

For this system (exact model): The project explicitly names the Atari 400. An external build can use a joystick-port plug; an internal build requires protected wiring behind the motherboard's in-line resistors.

The maker publishes beta firmware, source, a pinout, and programming files but not a finished adapter PCB on this page. A build requires a programmed PIC16F1847 and suitable wiring or an enclosure. For an internal installation, connect behind the computer's in-line joystick resistors so a plugged-in joystick cannot directly short the PIC outputs. USB mice work only when they also implement the PS/2 protocol.

Connects MIDI instruments or an optional DreamBlaster wavetable module to an Atari 8-bit computer through SIO.

For this system (exact model): The seller page explicitly names the Atari 400. Use the SIO2MIDI or SIO2MIDI-S2 variant, not the 1088XEL-only MIDI-XEL boards, and provide the required SIO cable and compatible MIDI hardware or software.

The storefront family was sold out on 2026-07-24, but MyTek publishes schematics, Gerbers, firmware, and bare-PCB order links for SIO2MIDI and SIO2MIDI-S2. SIO2MIDI-S2 does not route its synthesized sound through the Atari; use its headphone or speaker jack. The maker page also includes 1088XEL-only MIDI-XEL variants, which are not attached to factory-computer entries.

Provides open internal and currently assembled external SD-based SIO disk-emulator variants for Atari 8-bit computers.

For this system (stated family): The assembled SD Drive Mini is sold for Atari 8-bit computers and plugs directly into SIO. Use a FAT32 microSD card with SDRIVE.ATR; software that needs BASIC should use the Atari 400's cartridge rather than the XL/XE Option-key instruction.

Lotharek exposed a login-or-register-to-buy path for SD Drive Mini on 2026-07-27, and Retro Lemon also listed it with pricing. It plugs directly into SIO, uses a FAT32 microSD card and SDRIVE.ATR, and provides two buttons plus LEDs for selecting four drive slots. The separate open SDrive-Simple-II build still requires PCB assembly, ATmega328P programming, and an internal SIO connection. Its documented firmware supports cards up to 32 GB and ATR and XEX files, but not CAR, ROM, ATX, XFD, or CAS files, and it has no control for swapping disks in a multi-disk title. The former SDriveXEL assembled source and exact public build package remain unavailable.

Expands one Atari SIO connection into four peripheral ports with optional external power and bus-activity indicators.

For this system (bus/interface): The seller specifies Atari 8-bit computers and a standard SIO input. Supply the separate computer-to-hub SIO cable and avoid exceeding the available SIO power budget when attaching several peripherals.

Retro Lemon marked the assembled hub in stock and Lotharek exposed a login-or-register-to-buy path on 2026-07-27. Both pages describe the same one-input, four-output design with command, read, and write activity LEDs and a 4 mm acrylic top cover. An Atari SIO cable is required but not included. External power is normally unnecessary; when needed, use a 5 V center-positive supply for the 2.1/5 mm DC jack, which is also not included.

Emulates Atari 8-bit disk drives from SD or MMC cards through the SIO port.

For this system (bus/interface): The assembled seller says its SIO cable works with all Atari 8-bit computers and provides a fixed loader specifically for 400/800 machines. Use that loader rather than the XL/XE Option-key startup instructions, and confirm the installed firmware before relying on version-specific features.

Lotharek offered the Biggus Dickus, metal-cased XL and XE, and color variants through login-to-buy paths on 2026-07-27. The metal-cased versions include an SIO cable, while the base Biggus Dickus listing includes neither cable nor SD card; other listings bundle those accessories with the same hardware. The official project also publishes Eagle schematics and boards plus firmware, making a DIY path possible. Upstream firmware reached 3.3 in 2023, while Lotharek says its assembled versions use customized 3.1 RC2 firmware, so do not assume identical features without checking the installed version.

Replaces the 4050 video buffer and routes configurable conditioned video signals to the Atari's output connector.

For this system (exact model): The seller explicitly lists the Atari 400. Follow a model-specific signal and output-routing plan; the page's illustrated installation example is for an XE rather than the original 400 motherboard.

The product exposed a login-or-register-to-buy path on 2026-07-27. Installation replaces the 4050, connects GTIA pin 21 to the board's color input, and rewires output signals at the computer's video connector. A non-socketed 4050 and the output modification require desoldering and model-specific board work.

Connects a PS/2-compatible mouse to an Atari 8-bit or Atari ST-family computer.

For this system (exact model): The Atari 8-bit adapter page explicitly names the Atari 400. It is an external mouse adapter for compatible graphical software. A USB mouse works only if it implements the PS/2 protocol and is used with a passive adapter.

Both storefront collections marked their matching adapter sold out on 2026-07-24. A USB mouse works only if it also supports the PS/2 protocol and is used with a suitable passive USB-to-PS/2 adapter.

Connects an Atari 8-bit computer to a modern Mac or Windows computer for disk, cassette, modem, printer, and file-transfer emulation.

For this system (exact model): The product page explicitly names the Atari 400. Use a modern Mac or Windows computer, a suitable Micro-USB cable, and compatible host software configured for the adapter's DSR connection. A single-SIO version must be last in the chain or used with a splitter.

The Atari 8-bit collection marked all versions sold out on 2026-07-24. Dual-SIO versions can sit within an SIO chain; single-SIO versions must be at the end or on a splitter. All listed versions include a printed case and an 8 GB microSD card, but need a separate Micro-USB host cable and a Mac or Windows computer. Windows may also need a UART driver.

Adds clean composite and S-Video output circuitry to supported Atari 8-bit computers.

For this system (exact model): The product page explicitly names the Atari 400 and offers a model-specific all-in-one route with a plug-in UAV, internal audio board, and BOBby breakout. Use that matching configuration and the 400 installation instructions rather than assuming the generic CD4050 path.

The Atari 8-bit Rev. D page said Now shipping on 2026-07-24 and offered plug-in, basic, kit, and 1088 variants. Installation still requires soldering, output jacks, and the ability to follow a schematic. The vendor calls its large manual a starting collection and warns that not every machine has explicit or fully current instructions. The separate 600XL monitor port and BOBby audio/video breakout are installation accessories, not standalone upgrades.

Documents period DIY memory conversions that give an Atari 400 48 KB plus a banked 16 KB or an Atari 800 a 288 KB SuperRam configuration.

For this system (exact model): The exact Atari 400 procedure modifies its original RAM board and motherboard. It yields a conventional 48 KB system plus an optional bank-switched 16 KB, not a flat 64 KB address space.

These are historical, invasive board-level modifications rather than current kits. Both require extensive disassembly, trace cuts, soldering, stacked or perfboard logic, and staged electrical testing. The authors release the instructions for public use with attribution. The Atari 800 text lists six 41256 DRAMs, while human review found only one 41256 in its rough circuit sketch. The contradiction remains unresolved: do not treat the Atari 800 parts list or sketch as an authoritative build package without reconstructing and checking the circuit.