The 1K RAM on the ZX81 was not a lot to work with. A number of programs were written to fit in the restricted space but the real solution was more memory. In addition to the Sinclair and Timex/Sinclair RAM packs, many solutions were available, up to 64K RAM.
- 16-32-48K expanda RAM (Dancer) - Fits inside case.
- 16K or 32K RAM Plans (T. W. Cook) - Plans to expand 1K model to 16K or ZX81 with 16K to 32K for under $30. Fits inside ZX81.
- 16K RAM (Sinclair Place) - Gold-plated connectors and power LED. Manufactured by Indescomp.
- 16K RAM (Sinclair Research Ltd.) -
- 16K RAM (internal) (DK'tronics) - Internal RAM expansion for keyboard.
- 16K RAM Pack (JRS Software) -
- 16K RAM Pack (Suntronics) -
- 16K RAM Pack (Gladstone Electronics) -
- 16K RAM Pack (Compu-Pak) - Expansion for the Compu-board system.
- 16K RAM Pack (Audio Vision) -
- 16K RAM Pack (Dolphin Computer) -
- 16K RAM Pack (DK'tronics) - Available with or without a case.
- 16K RAM Pack (Namal Associates) - No enclosure RAM pack.
- 16K RAM Pack (KB Enterprises) -
- 16K RAM Pack (Kayde Electronic Systems Ltd.) - Works on Sinclair power supply.
- 16K RAM Pack (Laserscan Electronics Corp.) - Highly crash resistant RAM pack that can be mounted inside the computer under the keyboard or plugged into the rear connector. Requires no extra power supply; comes with a special high pressure edge connector.
- 16K RAM Pack (Ground Control) - Injection molded plastic case; overcomes wobble and disconnection problems characteristic of other units; optional extra is a keyboard sounder giving audible feedback when a key is pressed.
- 16K RAM Pack (Computer Add-Ons) - RAM pack physically similar to TS 1016. Claims not to suffer from wobble.
- 16K RAM Pack (RKL Systems) - Expandable to 32K.
- 2K Memory Upgrade (Cosmonics) - Kit to increase the ZX81 to 2K.
- 2K RAM Pack (DK'tronics) - Static RAM expansion; works with built-in RAM.
- 2K RAM Upgrade (Micro Logic Corp) - Upgrade for 1K ZX81. Includes 2K RAM chip, socket, jumper and instructions.
- 2K RAM Upgrade (Powertronix Electronics) - Internal upgrade; replaces existing RAM chips.
- 2K to 24K Memory Expansion (JST Enterprises) - Plans to expand memory up to 24K, using 2K RAM chips, placed anywhere from 8192 to 32768.
- 32K RAM (Sinclair Place) - Gold-plated connectors and power LED. Manufactured by Indescomp.
- 32K RAM Pack (RKL Systems) - Expandable to 64K. RKL joystick systems can be added to this unit.
- 32K RAM Piggy-Back (Gladstone Electronics) - Can be used standalone or with a 16K RAM for a total of 48K.
- 3K RAM Board (Quicksilva) - Static RAM; expands internal memory to 4K.
- 48K Memory Extension (Memotech) - Allows ZX81 to run 48K Basic programs including up to 16K of assembly code. ZX81 sits on custom built case containing the Memotech.
- 48K RAM Pack (RKL Systems) -
- 4K RAM Pack (DK'tronics) - Static RAM expansion; works with built-in RAM.
- 64K Dynamic RAM (John Oliger Co.) - 64K DRAM board for the TS1000, TS1500 or ZX81. Special features of this memory include: 8-12K on/off switch 12-16K on/off switch two banks of 8K ram available mapped 8-16K (Bank A/B switch) and 48-64K on/off switch
- 64K RAM (Sinclair Place) - Gold-plated connectors and power LED. Manufactured by Indescomp.
- 64K RAM (internal) (DK'tronics) - Internal RAM expansion for keyboard.
- 64K RAM Pack (CompuTech & Software Industries, Inc.) -
- 64K RAM Pack (Suntronics) -
- 64K RAM Pack (BARLOG Software) -
- 64K RAM Pack (JRS Software) -
- 64K RAM Pack (Sunflower Systems) - Self-contained memory expander, housed in metal.
- 64K RAM Pack (Computer Add-Ons) - RAM pack similar in shape to the TS 1016. Claims not to suffer from wobble.
- 64K RAM Pack (Compu-Pak) - Expansion for the Compu-board system.
- 64K RAM Pack (Gladstone Electronics) - Metal case, snug fit for no wobble.
- 64K RAM Pack (DK'tronics) - Available with or without a case. 8-16K area available.
- 64K RAM Pack (Audio Vision) -
- 64K RAM Pack (Dolphin Computer) -
- 64K RAM Pack (Namal Associates) - No enclosure RAM pack. 4K pages can be switched off.
- 64KT/64KZ (Independence Research) - 64K RAM upgrades which mount inside the TS 1000 or ZX81. Installs in a minute with no soldering, and easy to follow instructions. Disable the 10-12K, 8-12K, or 8-16K areas of memory with a switch. Models specific to the ZX81 and TS 1000.
- 6K memory (internal) (Zodex) - Add 4K or 6K RAM internally.
- 8K RAM pack (DK'tronics) -
- Complete Memory Plans (Spectra Computer Products) - Documentation packet that covers memory pack troubleshooting. Includes plans for constructing your own memory pack, EPROM reader and extending the memory of the 16K RAM pack up to 64K.
- CRAMIC-81 (Cambridge Microelectronics) - 16K RAM pack using CMOS 6116 static RAM chips for permanent data retention. Data can be stored almost indefinitely and loaded almost instantly with virtually zero chance of error. A long life (10 years) lithium battery supplies power in standby mode. In the active mode, power is taken from the ZX81. Used on its own,
- Decoder (John Oliger Co.) - Fits inside the ZX80/ZX81 and remaps internal RAM to 8-9K or 9-10K. For use with external RAM pack.
- Delta Device (Weymil Corporation) - Non-volatile memory designed by Wilf Rigter. 32K RAM with Rigter Operating System (ROS). File-handling system in less than 600 bytes. Includes: DIRECTORY: displays all programs stored in memory by name and length in bytes. 44 entries per directory. SAVE: transfers BASIC programs, variables, and machine code to storage. Works in conjunction with the NAME/RENAME features.
- Downsway 16K RAM Pack (Downsway Electronic Ltd) - Fully cased and compatible RAM pack.
- Downsway 64K Memory (Downsway Electronic Ltd) -
- Econo Tech 16K RAM Pack (EconoTech) - Budget model 16K RAM supplied without case, gold-plated contacts. Designed to prevent wobble.
- FD16K RAM (Fuller Micro Systems) - Memory expansion that fits inside the Fuller keyboard and requires the Fuller motherboard.
- FD64K RAM (Fuller Micro Systems) - Memory expansion that fits inside the Fuller keyboard and requires the Fuller motherboard.
- Hardwire RAM Pack (Indiana Software Group Inc.) - Kit and instructions to permanently connect RAM pack to computer.
- Hunter 8K Nonvolatile CMOS RAM/EPROM (Hunter Electronics) - Up to 8K RAM or EPROM; works with 16K RAM packs. Store your own system utilities or build a library of machine language routines. Can be used with any ROM or RAM.
- Internal 16K RAM Expansion (Independence Research) - PC board and instructions. Instructions, $7.95.
- Jigsaw 16K RAM (Gladstone Electronics) - Can be used with Jigsaw 32K Plus to upgrade to 48K. LED power indicator.
- Jigsaw 32K RAM (Gladstone Electronics) - 32K RAM operates in tandem with a 16K to provide up to 48K RAM. Compatible with the Data-Assette ZX99. LED power indicator.
- Jigsaw 64K RAM (Gladstone Electronics) - 64K RAM extends usable memory to 56K. LED power indicator.
- M-16 Memory Module (Byte-Back Co) - Stackable with Sinclair RAM or other M-16 modules to 48K.
- M-48 Memory Module (Byte-Back Co) - 48K RAM module.
- M-64 Memory Module (Byte-Back Co) - Low power, no extra power supply required. Area from 8-16K can be switched out in 2K increments to accommodate memory-mapped peripherals, EPROMs, etc.
- MEMIC-81 (Cambridge Microelectronics) - Contains one or two 2K (6116) CMOS RAM chips. Memory is addressed into the ROM area from 8K-16K in the ZX-81 memory map. The address at which each chip appears can be adjusted to any 2K section within that area. Lithium battery in the unit provides a back-up power while the computer is switched off.
- Memopak 16K (Memotech) - 16K RAM unit expansion capabilities through its piggy back connection and is fully compatible with Timex or Memotech 16Ks to give 32K RAM.
- Memopak 32K (Memotech) - The 32K Memopak could be combined with a 16K RAM for 48K RAM. It was initially incompatible with the 2040 printer.
- Memopak 64K (Memotech) -
- Memory board with I/O (Wisconsinc Electronics) - 16K or 32K and two 8-bit LS TTL input ports and two 8-bit latching output ports.
- Minimap (BASICare Microsystems, Inc.) - Memory mapping device to expand address space from 64K bytes to 1 megabyte. Organized into vertical 64K pages. Up to 16 pages can be supported. All memory can be dynamically defined from within a program, allowing (for example) a program in one segment to manipulate the contents of various data segments. A module in the
- MX-16 16K RAM (INSIGHT) - Expansion plus power supply.
- MX-16 RAM (PM Enterprises) - Expansion RAM pack.
- MX-48 RAM (PM Enterprises) - 48K expansion memory; with power supply.
- QS 16K RAM (Quicksilva) - Cased dynamic RAM expansion.
- RAM 08 (BASICare Microsystems, Inc.) - Low cost memory expandable from 2K to 8K. Located in an address space not used by BASIC. Ideal for data or machine coded routine shared by second program. A module in the BASICare Modular Expansion System.
- RAM 16 (BASICare Microsystems, Inc.) - 16K memory module. On-board address decoding permits simultaneous use of many RAM 16 modules in conjunction with Minimap. A module in the BASICare Modular Expansion System.
- RAM 64 (BASICare Microsystems, Inc.) - Arranged in 4 blocks of 16K; all can be used under MINIMAP control. On board address decoding allows simultaneous use of many modules with MINIMAP. A module in the BASICare Modular Expansion System.
- RAM Adaptor Board (Fuller Micro Systems) - Adapts Sinclair RAM pack to fit inside Fuller case.
- RAMPAK 16 (Micro Systems Development) - Flat RAM module. 16K.
- RAMPORT (Componedex Ltd.) - Integrated expansion system. Analog, digital I/O ports and 16K RAM expansion on one card.
- SCRAM Board (Silicon Mountain Computers) - Improved version of Hunter board. Comes with battery-backup to make memory non-volatile. Developed with Larken Electronics to support Silicon Mountain’s WRX-16-based high-resolution software. Mapped in the 8K from 8-16K block. Can be re-mapped to 16-24K or 24-32K. Three SCRAM boards can provide 24K RAM for the ZX81 or 40K for the TS 1500. BOARD ENABLE
- SCRAM-Wich (Silicon Mountain Computers) - SCRAM board with two 8K static RAM chips, mapped to the normal 16-32K RAM region. Top 8K can be switched out in 2K blocks, allowing you to keep machine-code above RAMTOP.
- SIN 16 (Apropos Technology) - Efficient design, uses less power. Gold-plated, heavy-duty connector prevents glitches.
- Strip down (Commonwealth Agency, The) - Prevent RAM wobble.
- SUPER SIN64 64K RAM (Apropos Technology) - 8-16K range can switch in/out.
- The Incremental 1.1 (East London Robotics) - Fits inside computer; plugs in, no soldering; up to 16K in increments of 2K. Uses 6116 static RAM.
- The Lip 16K RAM (Sinclair Place) - “The LIP” locks on to prevent the wobbles.
- TS 1016 RAM pack (Timex Computer Corporation) - Timex’s version of the Sinclair ZX81 16K RAM pack for the Timex/Sinclair 1000. This, and the Sinclair unit, were famous for “wobble,” a condition that resulted in resetting the computer and loss of memory contents. Users overcame this problem with a variety of solutions, including Velcro between the computer and RAM pack, oversized rubber bands,
- UM-16 16K RAM Pack (Byte-Back Co) - “Ultimate memory” RAM pack. Battery backup, reset switch, PROM/ROM socket.
- UM-64 64K RAM Pack (Byte-Back Co) - 64K RAM pack with additional features. 8-16K area selectable in 2K increments. EPROM socket for 2K/4K. Battery backup (6 AA batteries) powers RAM pack and computer for up to 30 minutes. ROM-RAM transfer: copy Timex ROM into the 0-8K area of RAM, flip a switch and operate out of RAM. Switch that only resets 16-32K
- ZX-Panda (Data-assette) - Contoured case fits snugly against the rear of the computer. LED power indicator. Expandable to 32K with plug-in module that fits inside the existing case.
- ZX-Panda Expansion Module (Data-assette) - Plug-in module for 16K Panda, extending the memory to 32K.
- ZX81 2K upgrade (Micro Basics) - Kit including instructions and IC socket.
- ZX81 2K Upgrade Kit (J. Balogh) - Double on-board memory to 2K.
