Changes

* [https://pdfcoffee.com/the-zx-spectrum-ula-how-to-design-a-micro-chris-smith-pdf-free.html The ZX Spectrum ULA ebook]

* [https://worldofspectrum.net/documentation/ ZX Spectrum documentation]

* [https://sinclair.wiki.zxnet.co.uk Sinclair Wiki]

* [https://worldofspectrum.net/pub/sinclair/ World of Spectrum file server]