rmay635703
Veteran Member
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 ???
Why then was the Lisa 5mhz?
Video, ram or ???
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Today’s stupid question if Motorola didn’t make 5mhz chips why...
- Thread starter rmay635703
- Start date
krebizfan
Veteran Member
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?
GiGaBiTe
Veteran Member
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.
There's definitely a design reason for the CPU running at 5 MHz, but I don't know what that is.
commodorejohn
Veteran Member
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.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?
2icebitn
Banned
The micro is specced at 5mhz? Or is it a 6 or 8, just clocked at 5?
krebizfan
Veteran Member
The micro is specced at 5mhz? Or is it a 6 or 8, just clocked at 5?
The Lisa CPU boards I have seen pictures of have either a MC68000G8 (the 8 MHz variant) or MC68000L6 (6 MHz). Yes, Apple left a lot of performance on the table.
2icebitn
Banned
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.
commodorejohn
Veteran Member
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.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.