Vortex Expansions RAM card

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BOS ROM exists at rom slot 6 and is decoded exactly (no repeat).

DFxx is decoded by the Vortex RAM Expansion (for BOS) and uses xx0xxxxx xxxxxxxx xxxxxxxx xxxxxxxx (same as other ROM expansions).

The FBBD port is decoded as: xxxxx0xxx0xxxx0x

This means just 3 bits are decoded for it.

Data written to the vortex RAM doesn't write through to main RAM.

On Reset the BOS rom is activated.

Bits 7 and 6 written to FBBD are ignored. Bit 5 is for enabling the ram expansion. Bit 2,1,0 set the bank.

Bit 3 is documented as enabling and disabling the ROM, but I found it didn't work exactly like that.

If bit 3 is set to 1, and upper ROM is enabled with port 7fxx, then ROM on the Vortex RAM Expansion is enabled in the range &c000-&7fff.

If bit 3 is set to 1, and lower ROM is enabled with port 7fxx, then ROM on the Vortex RAM expansion is enabled in the range &c000-&7fff.

If bit 3 is 0, then normal operation happens. ROM is visible in the range &c000-&7fff only if ROM slot 6 is selected and the upper rom is enabled with port 7fxx. When bit 3 is 0, the rom is not visible in the range &0000-&3fff at any time.

It is possible this part of my (arnoldemu) vortex ram expansion is broken, but all other operation works perfectly and the BOS rom is active at reset time and can be used as normal.

On my (arnoldemu) vortex ram expansion, the bus has the value 0. It seems the vortex is forcing the value on the bus.


RAM expansions card from Vortex, mounted between CPC464 mainboard and CPU/Gate Array. It won't fit on CPC664, CPC6128, or CPC+ boards. The card is not compatible with the standard dk'tronics-sytle Standard Memory Expansions.

Sold in different sizes of RAM as SP 64, SP 128, SP 256, SP 320 and SP 512. Resulting in a maximum RAM size of 576K (64K internal, plus 512K external). The smaller SP64-SP320 versions can be upgraded to SP512 by mounting additional RAM chips in the spare sockets. There is also a cut-down version, SP 64/M, which contains only 64K RAM, no BOS ROM, and which isn't upgradable.

The expansion was available directly from Vortex (germany) and also from Screens Microcomputers (uk).

Usable under BASIC and CP/M:


BOS (Banked Operating System) RSX drivers are included on EPROM (mapped to ROM bank 6). Providing following features under BASIC:

  • Banked BASIC programs (using |GOTO, |GOSUB, |RETURN commands, for example: |GOTO,bank,line)
  • Pseudo Floppy (unlike a RAMDISK, this "floppy" can be accessed only via special RSX commands)
  • Debugger (aka Z80 Monitor) activated via |MON (v1.0) or |XM (v2.1)
  • Printer Spooler
  • Plus some extras like |FAST and |SLOW

Note: Some of the RSX commands are always available, some only after typing |BOS.


PATCH.COM is included on cassette. After copying the file from cassette to disk, it can be used to upgrade normal CP/M to support the expansion RAM. Providing following CP/M features:

  • 62K TPA
  • RAMDISK (unlike the BASIC Pseudo Floppy, this acts like a regular disk drive)
  • Printer Spooler

Note: There is a bug/problem with COPY.COM no longer working after installing PATCH.COM. A bugfix is listed in the appendix of the manual.



See Installing Vortex Expansion RAM.



  • BOS (Vortex Banked Operating System) (RSX commands on built-in EPROM, mapped to ROM bank 6) (under BASIC, the RAM is used as program/data region, BASIC programs can |GOTO and |GOSUB to expansion banks)
  • Driver Cassette (includes PATCH.COM for upgrading CP/M to support the expansion RAM) (62K TPA, plus RAMDISK and printer SPOOLer)
  • Further patches - the manual contains additional patches for some BASIC and CP/M programs
  • Discology
  • RCPM (RAM CP/M, 1989-1990 by Günter Radestock) (RCPM is an alternative to the PATCH.COM from Vortex)
  • G-Paint 2.0 (by Günter Radestock)