microprocessor archeticture

Thread Starter

hamran

Joined Aug 21, 2006
10
hi everybody
i dont understand that the 8086 i said to be 16 bit microprocessor but its ram is 20 bit long for addressing and the registers is 8 bit long.....could u plz help me understand the archeticture
 

beenthere

Joined Apr 20, 2004
15,819
Hi,

The 8086 was a horrible kludge, as was the IBM 5051 computer, and MS DOS.

Your best bet for data on the 8086 is to go to Intel and get the huge spec sheet on the device. They built it, so they are the best source of information.

This must be a purely academic interest - right? Surely you are not planning to actually use one? I have a leftover 386 plus math coprocessor I'd happily donate to spare you that agony.
 

Papabravo

Joined Feb 24, 2006
12,767
hi everybody
i dont understand that the 8086 i said to be 16 bit microprocessor but its ram is 20 bit long for addressing and the registers is 8 bit long.....could u plz help me understand the archeticture
The 8086 architecture can process data in byte size(8 bits) or word size(16 bit chunks). The size of the address bus(20 bits) has nothing to do with the data size. Who ever said that it did?

AX is the 16 bit accumulator, AH and AL are the uper and lower halves.
Similarly for BX, CX, and DX

BP Base Pointer
SP Stack Pointer
SI Source Index
DI Destination Index

are all 16 bit registers with no ability to manipulate byte size data

CS, DS, SS, and ES are all 16 bit segment registers used in segmented addressing.

A horrible kludge eh. Und how many successful microprocessor designs are you responsible for Herr Doktor? Ja zero - I thought so.
 

beenthere

Joined Apr 20, 2004
15,819
Hi,

Unsuccessful as charged, but the 8086 was still a kludge. If IBM hadn't put its imprimitur on the chip, it would have been eclipsed by the 6800.
 

Papabravo

Joined Feb 24, 2006
12,767
Hi,

Unsuccessful as charged, but the 8086 was still a kludge. If IBM hadn't put its imprimitur on the chip, it would have been eclipsed by the 6800.
Did you mean the 68000. The 6800 was an early 8-bit offering. As I remember the big knock on the 68000 was that at 64 pins it was like putting an aircraft carrier on a PC board. The cost differential was sustantial. IBM correctly saw that hardware architecture was very nearly irrelevant. Software was everything. If you have the right software the hardware doesn't matter.
 

beenthere

Joined Apr 20, 2004
15,819
Hi,

Yep, dropped a zero. And yes, nobody cared a bit about the computer's innards. Many strange things happened with early desktops.
 

Sirropo

Joined Nov 24, 2006
3
Yes, 68000 was the better chip, Intel just happened to be at the right place at the right time to get their 8000 series chip its historical jump start.
 
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