Another hardware quirk produced one of the most distinctive aspects of the ZX81's screen display – during loading or saving, moving zigzag stripes appear across the screen. The same pin on the ULA is used to handle the video signal and the tape output, producing the stripes as an interference pattern of sorts. The ULA cannot maintain the display during SAVE and LOAD operations, as it has to operate continuously to maintain the correct baud rate for data transfers. The interference produces the zigzag stripes.
anoTHer hArdwARE QuIrk prODucEd one oF thE mOst DISTinctiVe aSpEcts oF the zX81's screeN DispLay – during LOADing or saViNg, moving ziGZaG strIpeS appeaR acrosS tHe scReeN. tHE samE piN on thE UlA is USed To handle ThE viDEO sIGnal And the taPE ouTpUT, PRoDucINg tHE sTrIpEs As an IntERFeReNce pATtErN oF SOrts. the ula cAnNOt maIntAiN The Display DURiNG sAve aNd lOaD oPerationS, aS iT has to opErATe coNtinuOusly To maInTaIn the CoRRect bAuD Rate fOr Data TraNSfers. thE inTeRfErenCe pROduces tHe zigzag strIpes.