72

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 original 8086, its execution overlaps with the previous/next operation, so the CPU can crank out one ADD reg,reg per clock. The Long Read (Caveat, there's a whole ...


61

Having the display vertical reduces the width of the cabinet. This means that a game machine can be fitted into a smaller space in a pub/bar, or in an amusement arcade where machines are in rows you can get more machines (potentially a third more) into the same space. One-third more machines means one-third more revenue. The orientation may also have been ...


57

Because it used to be necessary. While a battery-powered real-time clock is standard today, this wasn’t always the case. The very first IBM 5150 did not include an RTC chip; the system clock was maintained by the PIT interrupt running on the CPU, which in particular meant that disabling interrupts halted the system clock. When the computer was turned off, ...


49

For the simple reason that until relatively recently, it was very difficult to make a rewritable optical medium, but it was easy to make a rewritable magnetic medium. Magnetic tape as a recording medium has been a practical technology since the late 1930s, predating the digital computer. For comparison, CD-RW was introduced only in 1997, more than a decade ...


42

I researched this question online fairly thoroughly a while back. I could not find any reference to an AGP device that wasn't a graphics card. It wasn't exhaustive, and absence of proof is not proof of absence, but I strongly suspect no such cards were made. I also think there are technical and economic reasons that make it unlikely. It would have been a ...


38

The PDP-10 had 'byte instructions' that could process a sequence of bytes of size 1 to 36 bits. The byte pointer was a word containing an 18-bit word address (and the usual index/indirect indications) plus position and size of the byte within the word. It was common to use 7-bit byte sequences for ASCII text, which gave 5 characters per word and one (...


36

Yes, huge safety concerns as I remember engineers sitting inside the cabinets of large mainframes while it was running, fully powered, large currents in each cabinet powering fans. Cooling water being pumped through the frames. Huge wiring looms hanging across the floor to great logic analysers on wheeled trolleys; trip hazards. One person regularly smoked ...


34

Classic IBM 224 Dictating Unit using a magnabelt, often called a Dictaphone, although that wasa trademark of a different company. Introduced in 1966 and sold in high volume and worldwide, way into the 1970s. Seen here in action. So while being from IBM, it's in no way computer related. They are still a common find. Only complete setups, including the ...


33

The main issue with the 80186 isn’t with the CPU core itself, but with its integrated peripherals: they aren’t compatible with those used in the IBM PC, and they aren’t integrated in the same way either. The IBM PC uses an 8237 DMA controller at offset 0x00 in the I/O address space, an 8259 PIC at offset 0x20, and an 8253 PIT at offset 0x40. The 80186’s ...


32

Yes, it's possible to effectively change the volume if you're using Pulse Width Modulation (PWM), although the timbre of the note is also affected depending on playback hardware and psycho-acoustics. Dr. Blake Troise, who makes chiptunes under the moniker Protodome, describes how in a recent paper: The 1-Bit Instrument: The Fundamentals of 1-Bit Synthesis, ...


32

But why was the 8087 designed such that it needed a special socket? Because the 8087 is a processor EXTENSION, not another CPU. The 8087 has, except for a few lines, exactly the same signals and pinout as the 8086/88. The socket is, except for 4(?) lines, a one-on-one duplicate of the CPU socket. This includes signals that need to be connected between both ...


29

Your premise that the point of the Turbo button was originally to slow down the computer to be timing compatible to an IBM PC/XT is correct. There was demand for that function, because a some of software, mostly games, were not synchronized to any timing source, but just scaled with the CPU frequency. some examples I encountered at that time are: Bugs, 1982 ...


28

PIC: 7 bit address space The Microchip PIC family of CPUs specifically the 10, 12 and 16 series have 7 bits of address space. While 7 bits is not exactly 8 bits this shows that there are commercial CPUs still on sale and still widely used that have less than 8 bit address space (they are used for example for power management on some Macs and are the most ...


26

Write speed and endurance. Optical drive technology has been much slower to write to than magnetic Hard Disk Drives (HDDs). The erasable optical technologies that made it to mass market were much slower in write time than HDDs and in erase time. Their life before failure was in the 100's of erases. Optical drive use declined with the advent of USB flash ...


26

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 more directly wired to the D registers than the A registers. It thus became a performance enhancement, allowing the main ALU and the addressing logic to operate ...


25

Classic RISC CPUs like ARM ... instructions execute in one cycle ... This assumption is not correct. The ARM-2 CPU (VL86C010, one of the first ARM CPUs) took: Only one cycle for most operations (as you expected it) Typically two cycles if a jump/branch was done Up to 4 cycles for shift/rotate operations Up to 16 cycles for multiply operations Up to 17 (or ...


24

I believe that your presumption is incorrect: The vendor, having no way of knowing whose fault this is, has to take the machine back and try to debug it. The vendors did not have to take the machine back and if they did offer a repair service it was not free. I don't recall that MITS (vendor for Altair) offered a repair service but I know that Heathkit ...


24

Back in the 80s, it was an industry and market very different from today's PC world. The audience were mainly do-it-yourself people who wanted to create things, and to understand how they worked. So, of your suggestions, "Tradition" best captures that aspect. You'll also find that, in line with that mindset, writing individual programs was a main ...


23

The KENBAK-1 has 256 bytes of memory. I'm not certain whether it had an 8-bit PC. https://en.wikipedia.org/wiki/Kenbak-1


22

Short answer: If you are content with beeps, no. If you want arbitrary sound, yes. There's three ways to get sound out of the PC Speaker: Put the timer chip into square wave mode and send frequencies (actually countdowns) to the timer chip. This is cheap and what's used for most PC Speaker sound effects in games. 140Hz is a popular rate to do it at. Set up ...


20

(From the perspective of the electronics, that means the displays were drawn sideways.) Not necessary. There is no inherent reason for drawing sideways. A video circuit can easy be made for either, as line width and number of lines can be defined either way. This is especially true for early games, where electronics were rather special to type and so was ...


19

The purpose of the switch is to support CPUs that can work at different clock frequencies. However, the presence of a turbo switch and a frequency display on a case, do not necessarily imply that the CPU can actually work at different clock frequencies, because the case is a generic case which has not been designed for one specific CPU. Background I ...


19

I think the best you could do in some cases was alter the pulse width of the basic square wave the hardware could produce. That wouldn't really change the volume, but you could make the tone "thinner" or "fatter" at the same frequency. One advanced technique used by some composers and sound drivers was "dithering", in which high-frequency random noise was ...


19

That paragraph should be understood in the context of the preceding paragraph: The PC speaker was often used in very innovative ways to create the impression of polyphonic music or sound effects within computer games of its era Effects such as those used in Pinball Fantasies in particular involve very rapid changes to the sound output by the PC speaker, ...


18

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 preceding instruction has started. The pipeline length of an 80486 is 5 stages (IF → ID1 → ID2 → EX → WB). This means that an instruction ...


18

I'm one of the developers of the Rekursiv. Its biggest problem was its recursive nature. Basically if a page fault happened while executing a (microcode, recursive) instruction it wasn't possible to abort execution of the instruction, issue a memory fault and switch to a different thread while the fault was serviced. Instead, the entire processor halted ...


18

The Datassette has a digital interface, and since it is not meant to process audio signals at all, it allows directly writing sharp digital magnetic transitions to the tape, using a single monophonic read/write head. The written pulses are always written at same amplitude, so there is no variation between equipment. Also when reading the transitions off the ...


18

It starts with discussion about computers overheating, That discussion seams to include some quite vague memory, so I wouldn't put to much into here. Still, such buttons were available and even installed after market, depending on company or state regulations. A CRAY Y-MP EL used at TU München is a great example, with its big power off: (Picture taken from ...


17

Full disclosure: I worked on the x87 FPU of a 486-class CPU at a math-coprocessor company in the early 1990s and thereafter worked at AMD, where I was on the 3DNow! design team and the design team for the FPU of the AMD Athlon processor (also known as K7). The x87 FPU never acquired a flush-to-zero mode. In fact, denormal support was one of the major ...


17

The ABC 80 computer used a 5×9 character matrix, each interspersed with one row and one column giving 6×10 pixels per character. The followup ABC 800 models followed teletext specifications and thus also had 10 pixels per text row.


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