The MK14

MK14 Photo


Not an Acorn product but an important stepping stone to the creation of Acorn Computers.  Chris Curry worked with Clive Sinclair on the development of the MK14 as well as other Science of Cambridge/Sinclair products but eventually went his own way setting up Acorn Computers, the Acorn System 1 of course being the first Acorn product.

There are a number of theories as to why it was named the MK14:

Personally I go for the third option ! 

The MK14 was made by Science of Cambridge (later becoming Sinclair Computers and finally Sinclair Research), it was based on the National Semiconductors SC/MP (INS8060) processor and was sold as as a kit:

MK14 Kit Photo

As well as the basic machine a number of add-on boards became available as shown in this advert from Wireless World January 1980: 

Wireless World MK14 Advert January 1980

National Semiconductors Introkit

The starting point for the MK14 appears to have come from an earlier National Semiconductors product The Introkit:

National Semiconductors Introkit Photo

This was a much simpler computer that only came as a kit, the PCB also providing prototyping space for adding your own peripheral circuits.

The first versions required a Teletype for the 'user interface' which was not an option for the hobbyist so National Semiconductor produced an add-on kit which included a modified National Semiconductor's Novus calculator, you then just had to wire up the circuit on the breadboard area ! (as in the photo).

I have found a manual for the keyboard interface, again it has a resemblance to the MK14:

Here is a copy of the National Semiconductor SC/MP Kit Users Manual.

There were two versions of the OS depending on the 'user interface', the Teletype version was called KITBUG whilst the later keyboard version SCMPKB:

Interestingly the early version MK14 OS, SCIOS, still has SCMPKB as the title in the assembler listing in the manual !  I had access to an Introkit with SCMPKB fitted and can confirm this is exactly the same as the early version of MK14 SCIOS.

National Semiconductor produced quite a lot of other documentation for the SC/MP processor which will be of interest to MK14 owners:


There were a number of versions of the MK14 but details of the changes between versions are sketchy at best.  The 'early version' schematic is most likely the first version, the 'later version' schematic refers to a version 5 so I guess the 'early version' is version 4.  The 'later version' states that unused gates are used on version 5 so I'm guessing that version 5 includes the updated address decoding required for the VDU.

The modifications are described in this document, Address Decoder Mods (component references and pin numbers refer to the 'early version' schematic as they were changed in the 'later version').



The MK14 was initially supplied with National Semiconductors SCMPKB firmware, dubbed SCIOS this was then upgraded to a Version 2 which incorporated tape interface routines.  We now have (an unofficial) Version 3 which replaces the tape interface routines with a Fast Loader.  Follow this link to see full details of all the versions of SCIOS.

MK14 Add-ons

There were a number of upgrades for the MK14:

Sinclair had plans to develop the MK14 further including a QWERTY keyboard and eventually BASIC (NIBL) but these never saw the light of day probably because of the take off of the ZX80 ?  Interestingly these developments were discussed in a letter from Chris Curry MK14 Developments Letter.pdf.

Memory Map

Expansion Connector


I am compiling libraries of interesting articles, documents and software related to the MK14 and SC/MP Processor:


I have made a replica of an original MK14 and also have an enhanced MK14E system details for both can be found here:


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