What is it?

This little PCB is an internal upgrade to 16KB for the ZX81 from Sinclair. The ZX81 was for many of us an entry in the world of computing, it was a cheap computer for it's time. However, it has one major flaw, it only has 1KB (2KB for Timex Sinclair 1000) of internal memory. More RAM could be added with an optional 16K RAMpack, which connected to the expansion port on the back of the machine.

Why did you make it?

Although the RAMpack gave the ZX81 16KB of memory. it was notorious for the infamous 'RAMpack Wobble'. The RAMpack didn't have a good connection on the expansion connector and certain movement of the computer could cause a crash, resulting in losing work, etc. Upgrading the memory internally to 16KB solves this problem and it also frees up the expansion port.

What makes it special?

It makes the ZX81 more usable and the modification can be easily reverted to 1KB or 2KB, should that be necessary. It is also compatible with HighRes modes on the ZX81. It should be able to run WRX mode, but is also capable of running HRG8 mode, it has a 10K Ohm resistor between +5 volt (pin28) and Write Enable (pin27).

What do I get?

The 'ZX81 Internal 16K 'No Wobbly Expansion' comes as a fully assembled PCB. A 28 pin turned pin socket is included. Printed fitting instructions are also included.