S5-2.5 The 8086 Microprocessor

Work through these

• Evolution of microprocessors

  How the family got here, which matters because the architecture you are about to study is still visible in the machine on your desk. Short, and it gives the rest of the topic a reason to exist.

  NPTEL: Microprocessors and Microcontrollers · Course

• 8086 internal architecture

  The block diagram of a real processor rather than a generic one. The split between fetching and executing is the feature to notice, because it is an early form of the pipelining idea from an earlier topic.

  NPTEL: Computer Architecture and Organization · Course

• The flag register

  The bits that record the result of the last operation, and the thing every conditional jump reads. Small, and used constantly.

• Signal description under minimum and maximum mode of operation

  The pin level view, which is dry and is where the processor meets an actual board. Skim it for the shape and return when a hardware detail needs settling.

• Register organization and the segmented memory model

  The concept to get straight in this topic: a twenty bit address built from two sixteen bit registers is an awkward answer to a real constraint. Knowing the constraint is what makes the awkwardness make sense.

• Addressing modes

  The same idea as the earlier addressing modes item, now on a specific machine. Comparing the two lists is a quick way to see what is general and what is one designer's choice.

• Overview of the instruction set

  What this processor can be asked to do, taken as a survey rather than memorised. Aim to recognise the shape of an instruction rather than recall every mnemonic.

• Advanced x86 processors: salient features; real and protected modes

  How the line grew up: wider registers, and a mode that finally protected one program from another. Protected mode is the item with lasting significance, because every operating system since depends on it.

• Evolution of the Pentium processors

  The end of the story, and the point at which the techniques from the architecture topics above appear in a shipping product. A good place to notice how much of this subject is still in use.