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My take is a bit different: the early microprocessors were a big step backward in functionality. The 7090 was a 36-bit machine, while the Z-80 and 6502 were 8 b

by kens 5y ago

My take is a bit different: the early microprocessors were a big step backward in functionality. The 7090 was a 36-bit machine, while the Z-80 and 6502 were 8 bit. These microprocessors didn't support multiplication or division. The 7090 supported not only integer multiplication and division, but floating point. Even the 8086 didn't have floating point (without the 8087). The 7090 also had channels, basically a built-in DMA engine for I/O. But overall I agree with you that the assembly code is fairly similar as far as the basic structure. Some of the early computers have pretty strange assembly code that requires a big mental shift. For example the Honeywell 1800 with two program counters that can go forward or backward, or the IBM 1401 with its word marks and arbitrary-length words. For a lot of old IBM 7090 manuals, see: http://bitsavers.org/pdf/ibm/7090 http://bitsavers.org/pdf/ibm/7090

facorreia 5y ago
Thanks for sharing. This collection of manuals is very interesting.
msla 5y ago
The microprocessors owed more to the minicomputers like the PDP-11 than the mainframes.
- zozbot234 5y ago
  Early microprocessors like the Z80 and the 6502 were a lot weaker than even minicomputer CPU's, they were more like glorified calculator chips. The Intel 80386 and Motorola 68020 were notable for being among the first really popular micros to reach true parity with the minicomputer featureset.
TedDoesntTalk 5y ago
> the Honeywell 1800 with two program counters that can go forward or backward Wow! What is the point of that? How is it used?
- kens 5y ago
  The two program counters were first introduced in the National Bureau of Standards' SWAC computer. The idea was that you would use the second program counter for a subroutine call, and then switch back to the first program counter to return to your original code. I don't think anyone really used the backward counting on the program counter; as far as I can tell, that was a side-effect of all the registers being able to auto-increment or auto-decrement.

by kens 5y ago

facorreia 5y ago

Thanks for sharing. This collection of manuals is very interesting.

msla 5y ago

The microprocessors owed more to the minicomputers like the PDP-11 than the mainframes.

zozbot234 5y ago
Early microprocessors like the Z80 and the 6502 were a lot weaker than even minicomputer CPU's, they were more like glorified calculator chips. The Intel 80386 and Motorola 68020 were notable for being among the first really popular micros to reach true parity with the minicomputer featureset.

TedDoesntTalk 5y ago

> the Honeywell 1800 with two program counters that can go forward or backward Wow! What is the point of that? How is it used?

kens 5y ago
The two program counters were first introduced in the National Bureau of Standards' SWAC computer. The idea was that you would use the second program counter for a subroutine call, and then switch back to the first program counter to return to your original code. I don't think anyone really used the backward counting on the program counter; as far as I can tell, that was a side-effect of all the registers being able to auto-increment or auto-decrement.