Questions tagged [cpu]
For questions relating to CPU - central processing unit
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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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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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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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Who designed the ALi M1386SX core?
The ALi M1386SX is a 386 compatible microprocessor. I believe it was released around 1995, rather late for a 386 but since it was targeted at the embedded market (e.g. word processors and point-of-...
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Is it possible to raise the frequency of command input to the processor in this way?
In the 70's and 80's RAM chips worked at a lower frequency than the CPU.
That is, the processor worked at a frequency higher than the RAM.
We have that the CPU cannot receive one instruction from the ...
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When were the RCA CDP1804, CDP1805, and CDP1806 introduced?
RCA produced follow ups to its 1802 CPU, the CDP1804, CDP1805, and CDP1806. What years did they become available to purchase in?
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Timeline for PowerPC CPUs from various manufacturers
I am trying to assemble a timeline of PowerPC series processors. It is complicated by the fact that there were multiple manufacturers.
So far I have:
IBM POWER
1990 POWER1
1992 RSC
1993 POWER2
1998 ...
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How did Z8000 implement mul/div in few transistors with no microcode?
The Z8000 was Zilog's entry in the 16-bit microprocessor market; it was unsuccessful in large part, as I understand it, because it took too long to debug. According to https://thechipletter.substack....
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What were the release dates for the NEC V series CPUs?
I am trying to determine when the NEC V series CPUs became available. So far I have:
1982 µPD8088
1984 V20
???? V40
???? V41
1981 µPD8086
1984 V30
1988 V33
???? V50
???? V51
???? V53
1986 V60
1987 ...
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Who designed and manufactured the SA1 (RF5A123)?
The SA1 (also labelled RF5A123) is an enhancement chip for the Super Famicom/Super Nintendo.
It is based on the 65C816, which the Super Famicom's main CPU (the Ricoh 5A22) is also based on. It seems ...
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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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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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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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Was the Game Boy CPU a completely new layout?
As explained on the Wikipedia Game Boy article and Is the Game Boy Sharp LR35902 object-compatible with the 8080/Z-80?, the Game Boy used a custom CPU that was fairly close to being a superset of the ...
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What if ATX 12v P4 power connector was introduced 4 years earlier? [closed]
AT power supply handled +5 and +12 volts, +5 for ISA and processors, +12 for motors in disk drives.
In 1995 486DX2 was introduced with 3.3V core, so it derived that from a simple but inefficient ...
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Was the S-83 Personal CP/M CPU used in commercial computers?
The June 1984 edition of Practical Computing magazine (page 43) refers to the American Microsystems Incorporated S-83 CPU as a Z80 compatible CPU with an 8K mask ROM capable of holding Digital ...
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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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Did using a PAL display mode for Amiga Workbench slow down an NTSC machine?
Inspired by this question about the CPU frequency when booting the Amiga in PAL vs NTSC, I'm curious if the CPU frequency was affected by using the other display mode.
In other words, I used an ECS ...
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How does POST memory test work on a relatively modern (2000s) PC? Does it still test every single byte like on older ones?
I have an Asus eee 4G (AMI BIOS), I want to ask if this product actually overwrites the entire RAM during cold boot. I have the "Quick boot" feature turned off and I can see the memory being ...
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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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What are common instructions used to put the CPU into idle mode in the past? [closed]
I once did some tutorials on osdev.org and one interesting point was how the CPU is set into idle mode.
Because when no task has work to do you want to put the CPU into idle mode and not consume any ...
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Would compare-and-branch have added an extra cycle on ARM-1?
The ARM-1 was an early RISC CPU, designed in 1986 (and even more typical of early RISC design constraints than the year would suggest, since Acorn didn't have the budget to pay for the latest process ...
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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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Why was the size of the 1989 Intel i860 (aka 80860) memory bus 64bit?
On Wikipedia I have read the i860 from 1989 memory bus was at least 64bits wide.
(It is the first CPU the Windows NT kernel was running on.)
I think even 10 years later (1999) most desktop CPUs 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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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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Why does MOS 6502 require an external clock if it has an internal oscillator?
I have a trouble understanding how the MOS 6502 clock works. Possibly due to my extremely low knowledge regarding electronics in general.
According to the Wikipedia:
MOS would introduce two ...
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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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Can someone clear up principles of CPU caching and pipelining simply and precisely? [closed]
I am asking this here because from the history the principles might become much clearer than looking at the latest and greatest CPUs. Of course I know that "cache speeds up memory access" ...
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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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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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If I build a new CPU architecture, how would an OS like Linux know how to run it? [closed]
I am trying to build a CPU from scratch (from NOR gates) in an emulator first, then on breadboard. (Inspired by nand2tetris and Ben Eater)
Just trying to understand how things work.
Now, as my CPU ...
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How does the VIC-II/CPU memory access work on the C64?
As a programmer I knew that on the C64 the CPU got the bus in the high phase of PHI2 and the VIC-II got it in the low phase and also stole extra high phases when required.
However, it wasn't until ...
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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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Why 8086/8088 has OF in a high Flags byte?
In 8086, OF is put not into low Flags byte as other flags but separated in the second (high) byte. This is followed then in all the x86 line.
Beside the possible historical reasons, this looks highly ...
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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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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 CPU architecture was first to implement 'inverted borrow' carry flag during subtractions?
Background
In two's complement arithmetics, if one wants to calculate a subtraction having only an adder that calculates
{cout,result}=full_adder(arg1,arg2,cin),
where cin and cout are incoming and ...
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What is the relation between external clock and internal states in the 68000?
(I'm assuming a memory cycle of 500 ns, without wait states.)
According to the 68000 bus diagram, there are 4 CPU cycles for a memory cycle, so an external frequency of 8 MHz. However, things are ...
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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 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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Z80 - "LD (nn), dd" command cycle [closed]
For a university assignment, I have to describe and draw the command cycle of the LD (nn), dd command. To be exact, I was given this command:
LD (0x1000), BC
which I interpret as putting the low ...
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8088 CPU A16-A19 address lines go crazy with nop test after 0FFFF address
I'm building a minimal, minimum mode 8088 computer. I started with an 80C88-2 (CMOS, static variant) CPU. My configuration is really simple. One CPU, one 74HCT245 (DTR->DT/R) for the data lines, ...
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How were the popular CPUs of the eighties implemented? [closed]
With the ubiquity of FPGAs, I find it relatively easy to design an eighties-like CPU. But it's maybe too simple now, with so many ways to implement any given CPU unit.
What were the hardware ...
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Z80, do I need a resistor for pins to Vcc?
Building a Z80 computer after completing one with 65c02.
Z80 on my project needs some pins to be tied high (INT, NMI, WAIT, BUSRQ), these are the ones that I don't need for the time being. There are ...
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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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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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What's the heritage of 80286? [closed]
80186 introduced some instructions for HLL features.
80286 introduced some instructions for protected mode, and provided some multitasking ability with external MMU which was never intended for PCs ...
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Would there be any practical use of two or more VDPs or sound chips in a retro computer build?
Would that allow for better sound samples or double/triple the number of sprites & colours on screen or would that put too much pressure on the CPU or cause bottlenecks, maybe requiring 2 CPUs for ...
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CPU slaves on a PCI card to retrofit single processor to multiple processors. Any ideas how? [closed]
My desktop computer is no longer manufactured and no longer supported since more than 18 years ago. It was a very expensive top of the line business computer back in the day. I like it and wish to ...
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