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Questions tagged [cpu]

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13 votes
2 answers
3k views

Did the NES CPU save die area by omitting BCD?

The NES CPU was a copy of the 6502 with the BCD circuitry removed. As I understand it, this modification was motivated by a theory that BCD was the only part of the 6502 that was actually patented, so ...
12 votes
7 answers
5k views

Why didn't CPUs multiplex address pins like DRAM?

An important innovation for dynamic RAM was multiplexing address lines, so a 2^N-bit chip only needs N/2 address pins, which helps keep cost down. Why didn't CPUs match this? Setting aside e.g. the ...
10 votes
1 answer
3k views

Is there any DOS game before Quake era (1996) that makes heavy use of the FPU?

Quake was one of the earliest DOS games to show most gamers the importance of having a fast FPU to play with. Were there any other games (probably 3D) before Quake that started using the FPU? For ...
8 votes
3 answers
2k views

Test emulated 8080 CPU without an OS?

I've found a few 8080 CPU test suites available, but they all assume CP/M or a similar OS is already present and running - they call BDOS for I/O, etc. I'm working towards being able to run CP/M on my ...
0 votes
2 answers
769 views

What is the most performant "32-bit only" x86 CPU? [closed]

I am thinking of building an era appropriate early/mid-2000s gaming PC. One requirement is that the CPU should not support x86-64 instruction set, only the 32-bit instructions can be used. My guess is ...
18 votes
3 answers
2k views

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 ...
12 votes
5 answers
6k views

Did any CPUs have a special instruction for multiplying or dividing by ten?

I recall reading about a CPU from the 90s which had, in addition to normal integer multiply and divide instructions, also had a special set of instructions for multiplying and dividing by ten. Does ...
13 votes
11 answers
5k views

Did any 8-bit device ever merge a CPU core?

Looking at https://upload.wikimedia.org/wikipedia/commons/c/c1/Commodore-64-1541-Floppy-Drive-04.jpg I started thinking the following: There are too many chips in that drive. It is crying out for a ...
3 votes
0 answers
182 views

What aspects of microprocessor ISAs have been patented?

A key objective of RISC-V was that every aspect of the ISA must be based on an expired patent. It was felt that this is the only truly reliable defense against patent lawsuits. It is surprising that ...
14 votes
7 answers
5k views

Which CPUs have implemented trap on signed integer overflow?

All mainstream microprocessors from the 4004 on, have implemented signed integer arithmetic with twos complement and silent wraparound on overflow (by which I mean that the CPU itself will not trap, ...
3 votes
1 answer
698 views

What do the pins D0-D7 on the Intel 8080 exactly signify?

I am currently trying to create a FPGA styled simulator of the 8080 in C. I have a couple of questions regarding the D0-D7 pins. As far as I can see the D0-D7 lines are used in order to store data (a ...
9 votes
6 answers
823 views

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 ...
14 votes
2 answers
1k views

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 ...
15 votes
4 answers
6k views

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 ...
88 votes
9 answers
16k views

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 ...
19 votes
3 answers
3k views

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. (...
22 votes
3 answers
7k views

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 ...
6 votes
3 answers
2k views

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 ...
5 votes
0 answers
294 views

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-...
2 votes
1 answer
285 views

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?
16 votes
1 answer
1k views

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. ...
25 votes
1 answer
2k views

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 ...
5 votes
2 answers
397 views

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 ...
4 votes
0 answers
395 views

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....
5 votes
1 answer
380 views

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 ...
7 votes
0 answers
180 views

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 ...
36 votes
8 answers
9k views

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 ...
17 votes
8 answers
8k views

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? ...
28 votes
8 answers
13k views

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 ...
16 votes
4 answers
6k views

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 ...
4 votes
0 answers
566 views

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 ...
0 votes
1 answer
154 views

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 ...
27 votes
5 answers
5k views

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 ...
33 votes
4 answers
10k views

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 ...
4 votes
1 answer
247 views

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 ...
3 votes
1 answer
273 views

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 ...
18 votes
4 answers
4k views

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 ...
6 votes
1 answer
663 views

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 ...
38 votes
4 answers
8k views

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, ...
8 votes
3 answers
2k views

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 ...
-5 votes
2 answers
386 views

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 ...
13 votes
2 answers
1k views

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, ...
17 votes
2 answers
2k views

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. ...
11 votes
5 answers
3k views

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 ...
7 votes
1 answer
548 views

Did any computer actually use the KR580VM1?

The KR580VM1 (or КР580ВМ1) is a CPU from Soviet Ukraine that is not directly equivalent to any Western ones. It's basically an Intel 8080 with another register pair, H1L1, and another address space ...
6 votes
2 answers
1k views

What’s the last x86 CPU that didn’t place a limit on the size of a single instruction?

Although useless, it’s widely known the first Intel and derivative CPUs like the Z80 didn’t set a limit on the instruction size. This means that it was possible to fill the whole RAM/ROM with a single ...
-4 votes
1 answer
264 views

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" ...
0 votes
2 answers
1k views

Get himem.sys working on an AMI 1.06.09 bios (not on VM)

I tried many 98SE boot disks online, they all boot successfully on my mobile workstation from USB (C:\>), but all can't run the Windows 98SE Installer because of XMS Memory, giving an error like: ...
20 votes
4 answers
6k views

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 ...
-5 votes
1 answer
461 views

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 ...