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151 votes

Why did some early CPUs use external math chips?

Simple: Complexity. A 8088 had about 29,000 transistor functions, while an 8087 with 45,000 is almost double that. Integrating the FPU within the CPU would have made it three times as big, putting ...
Raffzahn's user avatar
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66 votes

Why did some early CPUs use external math chips?

So these math chips (I assume you're talking about floating point units, such as the 8087 and other coprocessors) were not always/usually included in the CPU because they were not required by most ...
Omar and Lorraine's user avatar
53 votes
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Why did some early CPUs use external math chips?

Another point not addressed in the existing answers relates to the latency associated with accessing an external coprocessor. The first math coprocessors, while much faster than doing the same work ...
Dave Tweed's user avatar
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39 votes
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What modification is required from a PC floppy for use in Amiga?

The differences between PC floppy drives and Amiga floppy drives are as follows: PC floppy drives normally answer to drive select 1 (DS1), internal Amiga drives answer to DS0 pin 34 on the connector ...
Stephen Kitt's user avatar
39 votes

Why did some early CPUs use external math chips?

It seems to me there are a number of factors involved, some of which have been addressed in other answers: design complexity cost (which largely results from the complexity) feature necessity time-to-...
Stephen Kitt's user avatar
36 votes
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Replacing 80286 with 68000

No, there is no simple one-to-one mapping for the pins. (Bolded signal names will be active-low.) For example, while the 286 has two physical pins for interrupts (INTR and NMI), 68000 has three (IPL0,...
telcoM's user avatar
  • 754
31 votes

What prevents faster versions of old architectures from being created?

If you look into real hardware (like a Motorola/Freescale/Rochester 68060, which is long out of mass production): Modern CPUs (mainly Intel) boosted to several GHz clock frequency have one main ...
tofro's user avatar
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24 votes
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Can a 16K computer be upgraded to 64K?

It all depends on the computer to be modified and its RAM system. For now, let's focus on the pure RAM expansion issue and drop the part about bank switching; as this is completely machine-dependent, ...
Raffzahn's user avatar
  • 226k
23 votes

What prevents faster versions of old architectures from being created?

Nothing stops anyone from creating faster accelerator cards (assuming Amiga or Atari ST - the only two platforms allowing for proper expansion cards), but there would be at least 3 major things to ...
Kuba Tyszko's user avatar
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20 votes

Replacing 80286 with 68000

Most obvious question first: why not puting itn on a ISA Card and take over the bus instead? Given, there would be still some work to be done after asking for DMA and pulling /MASTER, but way less ...
Raffzahn's user avatar
  • 226k
19 votes

What prevents faster versions of old architectures from being created?

Nothing actually prevents anybody of creating 2GHz 68060-like CPU. Or even highly-speculative out-of-order 68k-compatible one. All you need is tens (if not hundreds or more) of millions dollars to be ...
lvd's user avatar
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13 votes

Why did some early CPUs use external math chips?

This simple answer is not enough room on a chip for the total transistor count given the limitations of the process technology of the day. As per Wikipedia on the Intel 8087: The 8087 was an ...
Erik Eidt's user avatar
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12 votes

How does the 4MB mod for 8-bit Atari work?

Memory beyond 48 KB on 8-bit Ataris is all based on bank-switching, since the 6502 processor only has 16 address lines. The CPU can address 64 KB total, and that has to include ROM and memory-mapped I/...
Stephen Kitt's user avatar
12 votes
Accepted

Is there a way to trick my 386SX laptop into thinking there's a floppy drive installed?

The standard algorithm to probe for floppy drives (and tell 1.2MB drives from 360KB drives) is patented by IBM and yet cloned by most BIOS manufacturers. There were litigation lawsuits against Award ...
Michael Karcher's user avatar
11 votes

Can a 16K computer be upgraded to 64K?

The 4116 and 4164 have different pin allocations for the reason you'd expect: the 4164 has an additional address line (for two more bits of address in total because row and column are multiplexed). So ...
Tommy's user avatar
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11 votes

Why did some early CPUs use external math chips?

Like anything else, in the end, it was "ease of use" for some value of "ease" and "use". The primary motivator was performance, the specialized processors are just an extension of the maturity of ...
Will Hartung's user avatar
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11 votes
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How to build an ATA controller for the AT bus?

A proper ISA IDE interface is quite simple, but not as easy as it might sound. There are some strange corner cases you should consider for full AT compatibility. You can find schematics for ISA IDE ...
Michael Karcher's user avatar
11 votes
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Extending C128D Keyboard cable

You can absolutely do this, I've used a 6 foot extension like this before on my 128DCR with no signaling issues. You are correct that you need all 25 pins wired straight through which a normal DB25m/...
mnem's user avatar
  • 4,555
10 votes

Why did some early CPUs use external math chips?

We're so used to hugely complex and dense chips these days it's easy to forget that there was a time when the 8086, with "only" 29,000 transistors (no on-chip cache of any kind), was at the edge of ...
Anthony X's user avatar
  • 441
9 votes

What prevents faster versions of old architectures from being created?

Many older architectures were designed so that the speed of internal operations would be well-balanced with the speed of memory technologies that were available at the time. They were also designed ...
supercat's user avatar
  • 37.2k
9 votes

Why did some early CPUs use external math chips?

Many small CPUs available and used today for embedded designs do not have an onboard floating point unit - most of the AVR and PIC series, MCS51, some ARM ... 8 bit single-chip microprocessors were ...
rackandboneman's user avatar
8 votes

What prevents faster versions of old architectures from being created?

I haven't looked at the architectures, but I suspect that one factor will be that the architecture sometimes will have implicit assumptions about the micro-architectural implementation. To achieve a ...
Sean Houlihane's user avatar
8 votes
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Upgrades for the TRS-80 Model 100 portable

As you mentioned, you could upgrade TRS-80 Model 100's RAM to 32k. You can also get a REX chip, which uses the ROM expansion slot to provide additional flash memory. The TRS-80 Model 100 had several ...
Aaron's user avatar
  • 2,384
8 votes

How can I connect a PIA or VIA chip to the Apple IIc?

Ian Kim's Mockingboard 4C shows how it is done. This card includes a 6522 VIA chip (actually a 65C22 since those are still in production) as part of the daughterboard. It connects via the CPU socket. ...
Ian Brumby's user avatar
8 votes
Accepted

What is the purpose of ROM switcher mods in CDTV

I've seen a lot of information on CDTV ROM switchers, but it is still unclear to me what is the actual purpose of it. The CDTV is essentially an Amiga 500 sans keyboard and floppy but with CD and ...
Raffzahn's user avatar
  • 226k
7 votes
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Is it safe to provide 5V to CMOS RAM from PSU instead of CR2032 battery?

The datasheet for that part can be found here, it lists the maximum for VBAT as 4.0 V, so yes you do need to regulate down from 5 V.
Colin's user avatar
  • 224
7 votes

What prevents faster versions of old architectures from being created?

Many would agree that Motorola was in a much better position to develop their 68k into something fast and modern than Intel with their crufty x86 ;) But Motorola stopped and abandoned the 68k in ...
Rico Pajarola's user avatar
7 votes

Extending C128D Keyboard cable

I think it may be as easy as connecting male pins from one side to corresponding female pins on the other side, Exactly that. but need reassurance please. Would be shame to blow something up. For ...
Raffzahn's user avatar
  • 226k
6 votes

Can a 16K computer be upgraded to 64K?

In general on old computers, the whole address space will be used in some way or other, even with less than 64 KB RAM (for ROM or I/O). So you'll have to do bank switching of some kind, or you loose ...
dirkt's user avatar
  • 28.2k
6 votes

What modification is required from a PC floppy for use in Amiga?

Here (archive.org copy) is a site with specific instructions for converting PC drives from several manufacturers to Amiga replacement drives. Note that getting the disk ready signal to work is ...
v-joe's user avatar
  • 1,268

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