Questions tagged [microprocessor]

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50 votes
5 answers

Why did CPU designers in the 70s prioritize reducing pin count?

A lot of 70s era microprocessors were packaged in DIP packages with 40 pins. This was a reasonably good fit for 8-bit processors: 16 address lines, 8 data lines, 2 power and clock are all absolutely ...
  • 12.6k
99 votes
6 answers

Were there 8086 coprocessors other than the 8087?

The 8087 math coprocessor for the 8086 (and descendants) nominally added floating point and transcendental (trigonometric and logarithmic) instructions to the 8086. Contrary to naive expectations, the ...
  • 2,390
84 votes
9 answers

How much better was DEC Alpha than contemporaneous x86?

The DEC Alpha, released in 1992, seems like an early implementation of a fully 64-bit microprocessor architecture. Its release led to quite a bit of both marketing hype and genuine vendor support in ...
  • 58.9k
9 votes
3 answers

How does Game Boy / Sharp LR35902 HRAM work?

The Nintendo Game Boy has RAM called "HRAM" (meaning "high ram") decoded at locations $ff80 through $fffe. (All other decoded locations in the $ffxx page appear to be I/O device and system control ...
  • 22.9k
6 votes
3 answers

What is the MOS 6502 doing on each cycle of an instruction?

So, first off, I am kind of a noob with emulators and the 6502. Summarise the problem If we for example take the instruction ADC Immediate ($69) which adds the accumulator to an immediate value and ...
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37 votes
12 answers

Were there ever 12-, 24-, 48-, etc bit processors?

After seeing this question, I was struck with an intense curiosity to know: Were there ever processors with word sizes that aren't powers of two, specifically after the 8-bit byte became the industry ...
  • 685
34 votes
2 answers

Can the two CPUs in a Commodore 128 run at the same time?

The Commodore 128 has two CPUs. One is some variant of the 6502, and the other is a Z80. One CPU is there for compatibility with the Commodore 64 and the other is there presumably to give basic ...
30 votes
5 answers

How was microcode implemented in retro processors?

How was microcode implemented in retro processors such as the Z80 or 8080? Was the microcode standard (for example a manual for the processor outlining all possible micro-instructions and the ...
  • 1,965
21 votes
3 answers

What happened to the 65832?

In his June 1985 foreword to Programming the 65816 by David Eyes and Ron Lichty, Bill Mensch expresses his hopes for a 6502-derived 32-bit microprocessor: the 65832. WDC is still thriving, but the ‘...
  • 2,110
13 votes
1 answer

Intel processor transistor type evolution

The Intel 4004 used MOS (metal–oxide–semiconductor) transistors. What has been the transistor types used in Intel processors onwards from the 4004 to 8085 to the x86 family of instruction set ...
  • 1,767
6 votes
1 answer

Tannenbaum paper on constants in ISAs?

I see many references to a paper by Andrew Tanenbaum that demonstrated the vast majority of constants would fit into 13-bits, and I seem to recall it being in my university text on CPU design. However,...
3 votes
2 answers

How exactly do all control signals in 6502 work?

I'm trying to make a 6502 replica in Logisim. I want to know what exactly each control signal in 6502, how the clock cycles work and additionally I would like to see an example of these control ...
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