This is likely to be the most difficult to find piece of Philips Videopac hardware (together with the G7200 console). Very few are known to exist.

The C7420 is a hardware add-on that expands the C7420 into a full-fledged home computer. The C7420 adds a Z80 microprocessor running at 3.574 MHz, 16K RAM (two 4416 16K*4DRAMs in the add-on) and 18K ROM (one 2564 8K*8 EPROM and one windowless 2564 8K*8 PROM in the add-on and one 2516 2K*8 EPROM in the cartridge). 8K ROM is being taken up by the Microsoft Z80 BASIC. Next to the two RAM chips are two additional places with the same connectors - maybe there was a 32K RAM version planned. The rest of the board is filled with various logic chips, resistors etc. which are also used for the cassette port. Of the 16K RAM a little over 14K are user-accessible.

The C7420 can save programs to standard cassettes via its cassette port consisting of two standard 3.5mm plugs that connect to the headphone and microphone port and a 2.8mm plug (use is optional) that connects to a remote control port.

The C7420 has a graphics resolution of 320 * 240 pixels in graphics mode and 40 * 24 characters (consisting of 8 * 10 pixels) in text mode, up to 8 colors can be displayed at once. Up to 96 characters each are user definable in text mode and in graphics mode for a total of 192 user definable symbols. The BASIC also gives control over the sound generator.

In early ads the C7420 label merely stated 'BASIC', obviously the decision which Basic dialect to use hadn't been made at this point. Microsoft was known back then for its popular BASIC Interpreter for the 8080/8085 and Z80 microprocessors and the CP/M-80 operating system. After Philips had decided in favor of Microsoft, the BASIC was adapted to the unique features of the C7420 and the C7420 manual contains sections straight from the MS BASIC Interpreter User's Guide for the Z80. Also included (at least in the French version) are an errata correcting about 20 errors (interestingly enough the errata I have refers to C7420/19, see below), a warranty information card and a sheet recommending the use of certain Philips or Schneider tape recorders for program storage.

The label on the back states 'TYPE C 7420/XX', I've seen XX either being '00' or '20'. Maybe this is the revision or version - please let me know if you have seen other revisions. The accompanying errata refers to C7420/19.

I'm not sure about the original price of the C7420, it must have been higher than that of the Chess add-on C7010 which was between DM 300 - 400.