Search Posts:

Atari 400 With 32/48K RAM Expansion

SHARE

Return to Threads

  Atari 400 With 32/48K RAM Expansion by Bill Degnan - 05/16/2022 11:38
Atari 400 homebrew RAM expansion front. Click image for larger view.


Unlike modern RAM upgrades, this one is an actual vintage wire-wrapped 48K upgrade constructed in 1981 or so.

Atari 400 homebrew RAM expansion obverse. Note the wirewrap connections and pin 4 has been cut. Click image for larger view.


The wire jumpers added to the motherboard to allow for the RAM expansion to be made available to the system. Click image for larger view.



Here is the RAM expansion as it would appear installed within the Faraday cage (removed) within the Atair 400. Click image for larger view.



So how much RAM is available? Click image for larger view.


When I test the RAM in basic using the command ?FRE(0) the system reports 29690. In theory this RAM card has chips enough for 64K. I tracked down the original notes and schematic for this RAM daughterboard to see what was going on.

Apparently the board was originally wired for 48K. In 1984 pin 4 was cut to step down the board to supply RAM from 00-32K only. With the advent of the 16K game cartridge (such as Pole Position) RAM space 32K-48K was needed for the larger carts. Essentially without a switch (electronic or software) RAM expansion for a 400 maxes out at 32K, if you want to use 16K carts.

Download schematic and hand-written project notes and view photos

This particular Atari 400 was owned by Roy Brader. He won the computer prize drawing held by Avantec.

Reply

Resources:


Buy a Commodore Computer Poster

Popular Topics and FAQs


  • Commodore B Series Tips and Tricks
  • Aerocomp TRS 80 M 1 Expansion Unit DDC
  • Items Wanted
  • Lobo Max 80
  • Zenith Z-19-CN
  • Prototype PET 2001 photo
  • Using Toggle Switches to Analyze Memory
  • Commodore Disk Archive Project
  • PET 2001 Prototype at Gametronics 1977
  • Jim Butterfield Photo
  • IMSAI 8080 With Processor Tech. Cutter
  • Secrecy is the keystone of all tyranny
  • Cromemco System Three
  • Northstar Horizon - Boot Problem
  • Computer History and Restoration Links
  • Commodore BX-256-80 - 8088 Co-processor
  • S-100 board testing with Z-80 ICE
  • Donner 3500 - an early portable computer
  • Digital (DEC) PDP 11/05 NC Assembly
  • Univac 1219 rescue
  • IMSAI 1.4 BASIC vs. MITS 8K BASIC
  • Fido BBS listing node list 6-13-1986
  • PDP 8e
  • MITS 88-2 SIO (2SIO) for BASIC
  • Visual Technology Inc Model 1050
  • Amiga 2500 Restoration
  • The Evolution Of IBM Computers
  • Replacement teletype print hammer head
  • Archiving and Copying Software 101
  • Computers Built 1940 - 1950
  • CBM B-520 (a.k.a B256-80 or B500 256)
  • RCA COSMAC Microkit
  • Commodore 64K C-116 Mods
  • MITS 8800b Turnmon 9600 baud
  • Catweasel, 8in and 5 1/4
  • Raspberry Pi as Gateway to Internet
  • Digital PDP11 late 1969 early 1970
  • PDP 11/40 72 inch cabinet model
  • PDP 11/40 Industrial 11 model
  • Digitial MicroVAX 3100 30 System
  • Digital VAX 4000-200
  • Commodore 64 / 1541 DRIVEKNOCK
  • Booting the System Using RL02 drive
  • PACS: Reflections by Kathleen Mauchly
  • Tele-Graphic Computer Systems Inc.
  • Commodore B Series SID Jukebox?
  • Installing Core into PDP 11/40
  • Setting Up OpenVMS 7.1 DNS CLERK
  • Felt-Tarrant Comptometer Model J
  • NextStation Color
  • Digital Rainbow (PC100-B2)
  • 1970 Compusad Compulogical Tutor
  • Archiving Papertapes Using DSI NC 2400
  • 1976 P.C.C. Features the MAI JOLT 6502
  • 1961 Beckman DEXTIR Computer
  • UNIVAC 1 and UNIVAC File Computer 1
  • Past Issues:


    Hx16 backcover

    This image was selected at random from the archive. Click image for more photos and files from this set.