79 votes
Accepted

Why did 1950s-60s computers have such wide words?

And if you go back further, e.g. to the ENIAC, you'll see a word size of 40 bits. And if you go back even further, to mechanical calculators, you'll see word sizes determined by the number of decimal ...
dirkt's user avatar
  • 27.3k
77 votes

Why does the 80486 take longer to execute simple instructions than complex ones?

TL;DR: It's the pipeline. The 80486 contains parallel operating stages for decoding, operand fetch, execution and write back. So while an ADD reg,reg does take 3 clocks to perform, as it did in the ...
Raffzahn's user avatar
  • 223k
74 votes

What was the rationale behind 36 bit computer architectures?

Was there some particular design theory or constraint that made a 36 bit word size attractive for early computers? Beside integer arithmetic, 36 bit words work quite fine with two different byte ...
Raffzahn's user avatar
  • 223k
57 votes

Does the industry continue to produce outdated architecture CPUs with leading-edge process?

Manufacturing simple processors on newer semiconductor processes is done. But not quite to that extreme. Let's consider your proposed 8086 done in a 14 nm process. Let's say we do it in CMOS, and ...
RETRAC's user avatar
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49 votes

What motivated stack being invented originally?

The Stack, as we know it today, was developed by Friedrich Bauer and Klaus Samelson as part of their work on the Munich PERM and ALGOL. ALGOL-58 was in turn the first language to use a stack. They ...
Raffzahn's user avatar
  • 223k
48 votes
Accepted

On what computer did "JUMP" mean "don't jump?"

PDP-10. It had a very orthogonal instruction set based around mnemonics with suffixes, and depending on the operation, sometimes no suffix meant a NOP. http://pdp10.nocrew.org/docs/instruction-set/...
RETRAC's user avatar
  • 13.7k
48 votes

Does the industry continue to produce outdated architecture CPUs with leading-edge process?

TL;DR: Older CPUs have been shrunk to smaller sizes but not in the same way as modern design, simply as there is no gain in doing so. Details: Does the industry continue to produce outdated ...
Raffzahn's user avatar
  • 223k
46 votes

Why did ones' complement decline in popularity?

I imagine representations other than two’s complement (ones’ complement, sign/magnitude...) declined in popularity because two’s complement is simpler to implement; in particular: addition, ...
Stephen Kitt's user avatar
42 votes
Accepted

What is the purpose of mirrored memory regions in NES's CPU memory map?

It is not intentionally mirrored, it is just a side effect of making the address decoding hardware for RAM as simple and cheap as possible with a single common 74LS139 chip used for the task, when an ...
Justme's user avatar
  • 31.9k
42 votes

Does any computer resemble the model taught in UK secondary education?

Is there a computer that works like this? Erm, next to all? FETCH-DECODE-EXECUTE is the basic execution cycle for each and every digital CPU. No matter if a Turing Machine or a Pentium. I suspect the ...
Raffzahn's user avatar
  • 223k
40 votes
Accepted

Distinction between scientific and business computing

In practice, "scientific computing" meant floating-point number-crunching like physics simulations, and "business" computing meant I/O-oriented record processing, such as doing the ...
RETRAC's user avatar
  • 13.7k
38 votes

Why did DEC develop Alpha instead of continuing with MIPS?

The main thrust of the marketing behind the DEC Alpha was its 64-bit microprocessor architecture. They got there years before potential competitors, including MIPS. At the time DEC was shipping the 64-...
Brian H's user avatar
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37 votes
Accepted

What was the rationale behind 32-bit computer architectures?

there some particular design theory or constraint that made a 32-bit word size attractive for IBM to migrate to? It all comes down to the most basic data type, addressing constrains and, less ...
Raffzahn's user avatar
  • 223k
34 votes

How could early computers perform data operations before John von Neumann proposed the concept of ALU?

What von Neumann proposed was the idea of the ALU as a subsystem of an electronic computer, conceptually separate from the memory and input/output subsystems. The concept of hardware for doing ...
John Dallman's user avatar
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32 votes
Accepted

Why was there a need for separate I/O address space in addition to a memory address space already?

do not mention why or why not a single memory address space could be used from the beginning. Simply because a dedicated I/O space simplifies system design. It may be assumed that you're asking ...
Raffzahn's user avatar
  • 223k
29 votes
Accepted

Did the 68000 separate A/D registers save circuitry?

Each of the 68K series CPUs had dedicated address-generation hardware which was wired more directly to the A registers and had only limited access to the D registers. Conversely, the main ALU was ...
Chromatix's user avatar
  • 16.8k
29 votes
Accepted

Which computers did Donald Knuth "mix" together to get MIX?

Section 1.3.1 of The Art of Computer Programming says the following: MIX is the world's first polyunsaturated computer. Like most machines, it has an identifying number—the 1009. This number was ...
28 votes

What was the rationale behind 36 bit computer architectures?

36 bit word size attractive Many sizes have been tried, but fundamentally, this results in a certain precision; from Wikpedia on 36-bit Early binary computers aimed at the same market ...
Erik Eidt's user avatar
  • 3,357
27 votes

Why did DEC develop Alpha instead of continuing with MIPS?

and would have improved the chances of a single RISC architecture having wide enough industry support to achieve critical mass rather than being outcompeted by x86. It's important to remember that in ...
wrosecrans's user avatar
  • 2,264
26 votes

Does the industry continue to produce outdated architecture CPUs with leading-edge process?

They're not quite cutting-edge process sizes, but there are current 8051-core micro-controllers that do much better than the 1981 original's 12 MHz on 3.5-μm process silicon. For example, the Cast ...
scruss's user avatar
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24 votes
Accepted

Were there any 8-bit CPUs with 24-bit addressing?

Were there any 8-bit CPUs with 24-bit addressing? Not many. Most prominent and best fitting examples would be WDC 65816 of 1983 Hitachi 64180 of 1985 / Zilog Z180 of 1985 (only 19/20 bit) eZ80 of ...
Raffzahn's user avatar
  • 223k
24 votes
Accepted

Why the change in layout of single and double precision in floating-point registers?

When you have a small transistor budget, it is considerably easier to design your circuitry around a single representation format - the most capable one - and treat converting other formats to and ...
Chromatix's user avatar
  • 16.8k
23 votes

What was the rationale behind 36 bit computer architectures?

The key point made by Wikipedia seems to be: Prior to the introduction of computers, the state of the art in precision scientific and engineering calculation was the ten-digit, electrically powered,...
cjs's user avatar
  • 25.9k
23 votes
Accepted

What was the rationale behind 36 bit computer architectures?

I'm going to address the power of 2 part of the question. Keep in mind that before microprocessors, computers were assembled by hand. Increasing the number of bits in a computer was really a big ...
DrSheldon's user avatar
  • 16k
22 votes

Was the IBM 5100 ever used for codebreaking?

The 5100 had programmable microcode which could be used to implement crypto-specific opcodes1,2,3. Then there's the whole John Titor4,5 thing... 1 Such as population count 2 I'm unaware of anyone ...
Alex Hajnal's user avatar
  • 9,350
22 votes

Why did old consoles have special RAM dedicated for a specific task?

It's not limited to just consoles. Average PC in similar era than PS1 made the same distinction with several specialized memory areas for same reason. For example in a PC the CPU has memory it can use ...
Justme's user avatar
  • 31.9k
22 votes

Why did old consoles have special RAM dedicated for a specific task?

The most peculiar example of RAM dedicated to a single task was the Spanish version of the Amstrad CPC464, the CPC 472. This machine an extra 64kx1 DRAM chip which was not connected to anything. Its ...
Bruce Abbott's user avatar
  • 6,673
22 votes

What motivated stack being invented originally?

Given your reference to function pointers and function call patterns, I imagine you’re interested in call stacks. As far as I’m aware, these were first documented in Edsger W. Dijkstra’s 1960 paper, ...
Stephen Kitt's user avatar
21 votes
Accepted

Why does the 80486 take longer to execute simple instructions than complex ones?

First, it is not true that the 486 executes instructions in a single cycle. The 80486 is a pipelined architecture, so it's more accurate to say that most instructions can start one cycle after the ...
mcleod_ideafix's user avatar
21 votes

Any ways to have an architecture with a different base than base16?

Computers do not in general have "a base 16 architecture". They are binary, i.e., base 2. The base derives from the number of states a storage element can have. Almost exclusively, we use ...
dave's user avatar
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