We tried to measure Sprinter's speed and the result was, that it is approximately 3.5x faster than Spectrum, it means 12.5 MHz, not 21 MHz. Why? Is Sprinter so much slowed down by ULA or something?

CPU have 21MHz frequency.
When CPU use RAM its frequency is 10MHz-12MHz. Because RAM have 7MHz frequency and CPU waites data from RAM.
But Sprinter has 64K Fast RAM also. When CPU use Fast RAM its frequency is
21MHz.
You should set one of four pages (16K in one time) of Fast RAM to the PAGE 0
of CPU.

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PETERS PLUS LTD

and using ram more fast in simms ? :?

Not in SIMM. Mainboard Sp2000 use one chip W24515AK-15 for Fast RAM (this chip located under Flash ROM chip).

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PETERS PLUS LTD