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Another big mistake was to make the paragraph size 4 bits. Should have been at least 8 -- that would have given the 8086 a 24-bit address space, which would hav

by kabdib 4y ago

Another big mistake was to make the paragraph size 4 bits. Should have been at least 8 -- that would have given the 8086 a 24-bit address space, which would have made things verrry interesting in the MSDOS / early Windows world. (I know, they didn't have address pins on the 40-pin package. Still, an architecturally guaranteed 16MB of room to play in would have changed the face of the software industry in the 1980s).

manholio 4y ago
> an architecturally guaranteed 16MB of room to play in would have changed the face of the software industry in the 1980s I don't think it would have, because such amounts of RAM were prohibitively expensive into the late 80s. It would have changed the way software accessed the available RAM, made life easier for developers and improved compatibility be removing various kludges, but largely computers would have looked and behaved similarly, having largely similar specs.
- kabdib 4y ago
  VisiCorp was developing their VisiOn platform in the 1984-ish timeframe. They were bending heaven and earth to fit into 640K. Telling their corporate customers, "Buy another 512K of RAM" would probably have saved their company and let them ship a number of world-class productivity products, and given Windows some interesting competition. It's easy to second guess this stuff, on the other hand 512K of RAM was about $120 in 1985. We shipped the Atari ST with that much, when having that amount of memory on a Mac was pretty rare.
Gibbon1 4y ago
The way you'd deal with the lack of pins on a 40 pin package would have been to just no connect AD20-23.
- kabdib 4y ago
  Right, this is exactly what chips like the 68000 did.
dspillett 4y ago
> I know, they didn't have address pins on the 40-pin package. You are right that doesn't have to be a limitation on internal architecture: The 386SX internally had the 386's 32-bit data bus only 24 bits were carried out to the external pins. This, along with squeezing the 32-bit data lines through a 16-bit data bus by doubling up requests, made it able to be used on cheaper motherboards based on 286 designs. I'm not sure that this would have made enough difference to be worth the cost of the extra silicon at that time of the 8086's design though. While a flatter and more roomy address space would have been convenient to developers there would be little or no benefit for end users. The 386SX was a success because it could run software intended for the original 386 (then renamed 386DX) on cheaper hardware (and had the same MMU allowing virtual memory so could run larger software then it's 16Mb physical RAM limit made possible, at a further performance cost). Also the extra silicon requirements were not as expensive at the time the 386SX was being designed as when the 8086 was. In fact there was a chip that did similar for the 8086: the 8088. It had an 8-but external address bus and broke up 16-bit requests to make them over it. Though unlike the 386SX it maintained the same address bus of its relative.

by kabdib 4y ago

manholio 4y ago

> an architecturally guaranteed 16MB of room to play in would have changed the face of the software industry in the 1980s I don't think it would have, because such amounts of RAM were prohibitively expensive into the late 80s. It would have changed the way software accessed the available RAM, made life easier for developers and improved compatibility be removing various kludges, but largely computers would have looked and behaved similarly, having largely similar specs.

kabdib 4y ago
VisiCorp was developing their VisiOn platform in the 1984-ish timeframe. They were bending heaven and earth to fit into 640K. Telling their corporate customers, "Buy another 512K of RAM" would probably have saved their company and let them ship a number of world-class productivity products, and given Windows some interesting competition. It's easy to second guess this stuff, on the other hand 512K of RAM was about $120 in 1985. We shipped the Atari ST with that much, when having that amount of memory on a Mac was pretty rare.

Gibbon1 4y ago

The way you'd deal with the lack of pins on a 40 pin package would have been to just no connect AD20-23.

kabdib 4y ago
Right, this is exactly what chips like the 68000 did.

dspillett 4y ago

> I know, they didn't have address pins on the 40-pin package. You are right that doesn't have to be a limitation on internal architecture: The 386SX internally had the 386's 32-bit data bus only 24 bits were carried out to the external pins. This, along with squeezing the 32-bit data lines through a 16-bit data bus by doubling up requests, made it able to be used on cheaper motherboards based on 286 designs. I'm not sure that this would have made enough difference to be worth the cost of the extra silicon at that time of the 8086's design though. While a flatter and more roomy address space would have been convenient to developers there would be little or no benefit for end users. The 386SX was a success because it could run software intended for the original 386 (then renamed 386DX) on cheaper hardware (and had the same MMU allowing virtual memory so could run larger software then it's 16Mb physical RAM limit made possible, at a further performance cost). Also the extra silicon requirements were not as expensive at the time the 386SX was being designed as when the 8086 was. In fact there was a chip that did similar for the 8086: the 8088. It had an 8-but external address bus and broke up 16-bit requests to make them over it. Though unlike the 386SX it maintained the same address bus of its relative.