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Today’s stupid question if Motorola didn’t make 5mhz chips why...

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rmay635703

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Just curious all cpu photos I can find list the Motorola 68k as coming in 4, 6, and 8 MHz clockings

Why then was the Lisa 5mhz?

Video, ram or ???
 
Video probably. DOTCK (the primary clock signal) is 20.375 MHz and used as is for video and divided by 4 to give the CPU clock. Why Apple tried to save a few dollars on a $10,000 workstation by not having video and CPU on unrelated clocks is a mystery to me?
 
Just because a CPU is rated for a given speed, doesn't mean that it must run it at that speed.

There's definitely a design reason for the CPU running at 5 MHz, but I don't know what that is.
 
krebizfan said:
Video probably. DOTCK (the primary clock signal) is 20.375 MHz and used as is for video and divided by 4 to give the CPU clock. Why Apple tried to save a few dollars on a $10,000 workstation by not having video and CPU on unrelated clocks is a mystery to me?
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Probably this, but RAM also seems like a good guess; if they could get a better deal on slower memory components, that might've seemed like reason enough. But yes, one has to wonder why exactly they would cut corners to such an extent on a machine they were charging so much for, especially given that they were able to bring out the Mac running at a full 8MHz just a year later.
 
2icebitn said:
Never knew this. Wasn't the original Mac 7.16? Or was that the Atari, and Mac was 8mhz? Or the Amiga was one or the other. I'm so confused.
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If Wikipedia is to be believed, the Mac 128k ran at 7.8336 MHz - so not quite 8 MHz, but pretty damn close. The Amiga was 7.16-ish in NTSC territories, IIRC.
 
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