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1

You have shifting, so there's always some multiplication support.


2

Prior to microprogrammed/PLA-programmed processors, it took an enormous amount of control logic to manage a simple multiply (and forget about even trying floating point). Especially with early single-chip designs there simply was not enough chip space for the control logic. With the invention of microprogrammed processors it became more practical to include ...


1

cost tradeoff vs time to compute faster that is why the 8086 was that way and they had the 8087 if you wanted faster math z80 was just a newer slightly better version of the 8080


5

From the beginning of electronic computation, this was a common design decision when building a computer using minimal circuitry. The Manchester Baby, operational in 1948, had no multiplication hardware. Later, low end minicomputers such as the PDP-8 lacked hardware multiplication. For some, like the PDP11/20, there was an add-on peripheral for it.


4

It seems to be purely arbitrary (or pragmatic) choice of the designers, one of the main factors being the size of microcode ROM or PLA. As an example, I'll take soviet K1801VM1 CPU. Its latest modification, VM1G, does support multiplication. The only change is microcode, not even the size of microcode ROM or PLA. For the reference, look at this reverse-...


11

Slow multiplication implementations made with conventional ALUs and microprograms had another problem. There are a lot of machine cycles to execute a command. So much so that it becomes noticeable with intensive interrupt work. And for 8-bit microprocessors, with the exception of the case with the Atari 2600, working with interrupts generated by the graphics ...


54

You don't need it Multiplying two arbitrary bytes together has limited practical value. (If you want to multiply by a constant you can hardcode the optimal sequence of instructions to do so.) Obviously it would be nice to have but the expense isn't worth it. In an arcade game... you basically never need to multiply a thing. To draw lines or circles, you can ...


59

Fast multiplier circuits as used today take enormous amounts of logic, far beyond what would have been cost-effective (or perhaps even possible) in the mid-70s for an inexpensive microprocessor. Even slow multiplier circuits (as would appear later on chips like the 6809, 68000 or 8086) use a fair bit of logic and would have very considerably added to the ...


3

As per the other answer, in your case the yellow wire is not needed - it's a tacho signal that shows the current fan speed. It is possible to physically plug the new fan into the old connector with only the red and black wires connecting to the board. However the pinout of the fans are not compatible at the moment - the red and black wires are reversed which ...


8

Just plug it in, making sure the red and black wires are the ones on the pins. The connector should be keyed to enforce this. The yellow wire is for monitoring the fan's speed, and isn't required for normal operation. You may need to swap the wires around if the keying doesn't match. This is simple enough: the connectors are held in place by small springs,...


1

Working from memory and in addition to what everybody else has said, the order of the memory access and SP increment/decrement in the push and pop opcodes changed relative to the 8086 and 8088. This was the standard way of checking whether a CPU was an 88/86 or a 188/186. You could distinguish between the 88/188 and 86/186 by using self-modifying code to ...


18

I'm one of the developers of the Rekursiv. Its biggest problem was its recursive nature. Basically if a page fault happened while executing a (microcode, recursive) instruction it wasn't possible to abort execution of the instruction, issue a memory fault and switch to a different thread while the fault was serviced. Instead, the entire processor halted ...


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