Questions tagged [cpu]
For questions relating to CPU - central processing unit
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Why is the processor instruction called "move", not "copy"?
Many processors have an instruction called "move" (sometimes spelled MOV) which copies data from one location (the "source") to another (the "destination") in registers and/or memory. It does not do ...
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Why didn't early single-chip CPUs support multiplication instructions
Early single-chip silicon CPUs like the Zilog Z80 or MOS 6502 did not have a multiply instruction at all. Was this because the technology did not exist at the time to implement it, was it too ...
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Z80 CPU address lines not stable
I just got a Z84C0020PEC and wired it up to test it, using this circuit:
Except that I've added LEDs to A0 through A9. It appears that A0 through A6 operate correctly, but A7 though A9 (I've not ...
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What motivated stack being invented originally?
In the very early days (the earlier the better! Babbage maybe?) when something like a stack was developed, what motivated it originally?
I am aware that these days it makes many features possible, ...
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Can an x86 CPU running in real mode be considered to be basically an 8086 CPU?
When an x86 CPU is running in real mode, can it be considered to be basically an 8086 CPU (or maybe 8088)? Or are there differences between the two?
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Does the industry continue to produce outdated architecture CPUs with leading-edge process?
Intel has named the i7-8086K in honor of the 8086 processor, though itself it is a 64-bit processor. And we still see in embedded systems or MIL-SPEC platforms there are old CPUs like the 80386 ...
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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 ...
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How much did IBM save by limiting the PC to 4.77 MHz?
My understanding is the CPU clock speed on the Intel 8088 in the IBM PC was selected as 4.77 MHz to simplify the design of the system. This despite the 8088 coming in two versions - 5 MHz and 8 MHz. ...
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How did people program for Consoles with multiple CPUs?
I'm specifically interested in the Sega Mega Drive/Genesis, which used a 68000 CPU, but also a Z80, mainly used to control the sound hardware and provide backward compatibility with the Master System.
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Why was manual branch suggestion abandoned?
Once pipelined CPUs became common, a common issue arrived as a result of taking the wrong branch of a conditional jump, and thus needing to flush the pipeline. As a result branch prediction mechanisms ...
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Intel CPU bug in the 90s
My teacher who teaches "Logic" at the university told us a story about Intel processors, which goes: "In the 90s, Intel had a bug in the calculation of mathematical functions like sine ...
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Why did post-8008 CPUs not keep the on-chip stack idea?
Ken Shirriff writes in his blog entry about the 8008:
The 8008's seven registers are in the upper right. In the lower right is the address stack, which consists of eight 14-bit address words. ...
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Why did Intel abandon unified CPU cache?
When Intel introduced the 80486 in 1989, they included their first on-chip cache, ostensibly to compete better with Motorola, who had been including on-chip caches for 5 years (MC68020, 1984).
Unlike ...
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Why was desktop CPU frequency so low in the late 1990s?
I think even in the 1990s it wouldn't have been a problem to build a 4GHz clock generator.
Increase a transistor here and a resistor there and the clock rate will go up.
(I know there was DECT in the ...
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Did underclocking the early Z80 chips improve yield?
The Z80, one of the most successful and well-known of the 8-bit microprocessors, was released in July 1976 at an initial clock speed of 2.5 MHz.
The TRS-80 Model I, released the following year, is ...
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Do instruction exercisers exist for 8086 and 68K (and other) CPUs?
For some of retroCPUs there exist exhaustive instruction exercisers, i.e. programs that are capable of catching the implementation errors when run on the emulator under development or on the newly ...
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What was the last non-monolithic CPU to come to market?
This answer to the question "What was the rationale behind 36 bit computer architectures?" makes the point that early computers were assembled by hand, rather than having central processing ...
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How was the 80186 incompatible with the IBM PC?
According to https://en.wikipedia.org/wiki/Intel_80186
The 80186 would have been a natural successor to the 8086 in personal computers. However, because its integrated hardware was incompatible with ...
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MOS 8502, just a 6510B?
I'm looking over what little I can find on the 8502, and from what I can see it appears to be a 2 MHz version of the 6510 with an extra I/O pin.
Much ado about the speed, but the Atari's 6502B's were ...
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What was the last x86 CPU that did not have the x87 floating-point unit built in?
This Wikipedia page says the following:
Most x86 processors since the Intel 80486 have had these x87
instructions implemented in the main CPU
So the above quote implies that some CPUs that were ...
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Will PC-DOS run faster on 4 or 8 core modern machines?
When I run PC-DOS on my 4 core AMD Phenom chip, does it take advantage of the extra parallel CPU's? If not, is there a way to coax DOS to use all available CPU's or does this require specific ...
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How could the Intel 4004 address 640 bytes if it was only 4-bit?
I am reading Computer Organization and Architecture, 10th ed. by William Stallings and I found this on page 26.
where it says the addressable memory of 4004 is 640 bytes.
But it appears that the ...
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What does the "x" in "x86" represent?
I have read the following in the x86 Wikipedia page:
The term "x86" came into being because the names of several successors to Intel's 8086 processor end in "86", including the 80186, 80286, 80386 ...
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Does any computer resemble the model taught in UK secondary education?
In UK secondary education, there's a model called the fetch-execute cycle, which describes how computers work. (See: Isaac CS; Bitesize GCSE, Higher; Teach CS.) As I understand it:
The processor has ...
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Were there any 8-bit CPUs with 24-bit addressing?
Or was that something that didn't appear until later CPUs (around the time of the 286 maybe)?
Also, how would I go about researching this on my own? It's not exactly something I can look up on ...
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Why did Socket 3 have more pins than needed for the 486?
Intel's Socket 3, used for 486 processors, was a 19×19 pin grid array socket. However, all compatible processors, to my knowledge, used 17×17 PGA packages. What was the point of the extra pins around ...
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How much space did the 68000 registers take up?
The Motorola 68000 has 16 (somewhat) general-purpose registers of 32 bits each, a generous complement by the standards of its day. I would expect these to take a significant fraction of the die area. (...
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What are the screws for on the UltraSPARC?
I fail to grasp what can be screwed on them, can you explain what are these for?
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What was the first CPU with exposed pipeline?
Quoting from Programming for Performance exercise:
early versions of the MIPS processor had an "exposed pipeline" (that is, the assembly language programmer needed to know the latencies of ...
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Has there ever been a instruction set architecture that did not require instruction decoding at all?
I am studying basic principles of instruction set architectures and am considering what it would take to not have any instruction decoding at all. I.e., all the control lines of the computer would be ...
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DEC Alpha: why no 8/16-bit load/stores?
The first version of the DEC Alpha had no load/store instructions for 8 or 16-bit values; if you wanted to deal with data of such sizes, you had to do it by shifting and masking values in registers as ...
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When did the 386 overtake the 286?
The Intel 80386 was released in 1985, but was initially expensive, and took a long time to fully displace the earlier 80286 from the market; subjectively, I remember significant numbers of 286 ...
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Why would installing a 486DX2 make the system freeze for minutes on boot?
In the mid-1990s, a friend of mine had one of those Compaq Presario desktop PCs that had an integrated CRT SVGA display built in the same cabinet as the CPU, in a similar fashion as the early iMacs. ...
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Why did they create PC games relying on a fixed CPU frequency instead of a clock function?
I know there have been computer games which rely on a fixed CPU frequency. Instead of a clock function they rely on the fact that the CPU needs some time to execute the code.
But why did they do it? ...
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Does the Intel 8086 CPU have user mode and kernel mode?
Does the Intel 8086 CPU have user mode and kernel mode as modern CPUs do? and if it doesn't have user mode and kernel mode, does that mean that any user program written for the Intel 8086 CPU could do ...
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Why did some CPUs use two Read/Write lines, and others just one?
Many 8-bit processors, such as Motorola's 6800 and MOS Technology's 6502 make use of a single pin to indicate to the rest of the system whether the CPU wishes to read from or write to a memory ...
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What was the release date of the MOS 8502?
I have been unable to find when the MOS 8502 was first released to customers. The process it was made on was available from 1979, but MOS don't appear to have used it for their own parts at that time.
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How do accelerators and CPU cards work on the Apple II?
An Amiga 1200 exposes the entire CPU bus on the expansion port, so that an accelerator only needs to assert BR which causes the onboard CPU to stop all computation and electrically disconnect from the ...
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What was the last x86 processor that didn't have a microcode layer?
In the earlier days of microprocessors instructions were hard-wired, i.e. a particular instruction triggered circuitry that was mostly (if not completely) implemented for that instruction. I believe ...
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How could early computers perform data operations before John von Neumann proposed the concept of ALU?
According to Wikipedia, John von Neumann proposed the Arithmetic and Logic Unit concept in 1945.
Mathematician John von Neumann proposed the ALU concept in 1945 in a report on the foundations for a ...
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Does the Intel 8085 CPU use real memory addresses?
The Intel 8086 CPU uses memory segmentation, which means that when, for example, you write the value 123 to the memory address 1001, the memory address 1001 will actually get converted first into ...
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When was the 6502 second sourced?
According to https://en.wikipedia.org/wiki/Second_source
MOS Technology licensed Rockwell and Synertek to second-source the 6502 microprocessor and its support components.
This makes sense; the 6502 ...
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Resources about 1980s GPCPU video controller designs
Reading about the Fujitsu Micro 7, I found out that it used a pair of 6809 microprocessors: one as main CPU and one as graphics processor.
That made me remember that when running old arcade games with ...
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Did any RISC CPU ever take more than one clock cycle per instruction?
Classic RISC CPUs like ARM and MIPS basically offer the trade-off: simple instruction set, but instructions execute in one cycle for good overall performance. (It gets more complicated in later times, ...
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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 ...
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How did 2-chip CPUs work?
The 1970s saw a big transition from CPUs built from thousands of discrete components, to CPUs implemented on a single chip, with the occasional use of bit-slice components along the way.
There were, ...
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When did the natural number of branch delay slots become greater than 1?
Some early RISC CPUs had branch delay slots, the theory being that this would make the CPU both cheaper and faster; you could omit some interlock circuitry, and at the same time, in some cases, ...
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How did the CP1600 CPU supposedly make looping faster?
I came across an Intellivision in a box of stuff. When I looked it up on Wikipedia, it said that it uses a CP1600 that is based off a PDP-11. There's a weird entry on the wiki page:
CP1600 did not ...
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What was the first microprocessor to support full virtualization?
Virtual memory, which allows an operating system to run several machine code programs isolated from each other, came to the desktop during the eighties. But full virtualization, which lets the ...
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Performance of the Rekursiv
I happened to find out about the Rekursiv today. Rekursiv is a processor that attempted to implement OOP concepts directly at the hardware level.
Since it never got fully developed, I wonder what ...
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