Wednesday, July 19, 2006 

Processors overview

I read too many books for the intro of Assembly language and processors every one starts with 8086 or 80386. They are considered as base processors... well 8086 is the basic is famous for its real mode (which is outdated in this 32 bit world ) but still 8086 will serve as a good prototype... and 80386 the basic processor for 32 bit Intel based processors and can run in protected mode (this is the mode where the current windows, linux os) well 64 bit processors and OS are also out... but I *GUESS* they too run in protected that is simillar to 32 bit only difference being the 64 bit registers, 64 bit bus architecture ?...

DONT GET CONFUSED BY SEEING REAL, PROTECTED MODES for now just remember that they are some way of accessing & representing memory...

Well the following is the list of various major processor's of pentium from 8086 to pentiumIII listed with differences in
Dr.Paul Carter's book on assembly.The book is free, please download it from his website

8088,8086: These CPU’s from the programming standpoint are identical.
They were the CPU’s used in the earliest PC’s. They provide several
16-bit registers: AX, BX, CX, DX, SI, DI, BP, SP, CS, DS, SS, ES, IP,
FLAGS. They only support up to one megabyte of memory and only
operate in real mode. In this mode, a program may access any memory
address, even the memory of other programs! This makes debugging
and security very difficult! Also, program memory has to be divided
into segments. Each segment can not be larger than 64K.
80286: This CPU was used in AT class PC’s. It adds some new instructions
to the base machine language of the 8088/86. However, its main new
feature is 16-bit protected mode. In this mode, it can access up to 16
megabytes and protect programs from accessing each other’s memory.
However, programs are still divided into segments that could not be
bigger than 64K.
80386: This CPU greatly enhanced the 80286. First, it extends many of
the registers to hold 32-bits (EAX, EBX, ECX, EDX, ESI, EDI, EBP,
ESP, EIP) and adds two new 16-bit registers FS and GS. It also adds
a new 32-bit protected mode. In this mode, it can access up to 4
gigabytes. Programs are again divided into segments, but now each
segment can also be up to 4 gigabytes in size!
80486/Pentium/Pentium Pro: These members of the 80x86 family add
very few new features. They mainly speed up the execution of the
Pentium MMX: This processor adds the MMX (MultiMedia eXtensions)
instructions to the Pentium. These instructions can speed up common
graphics operations.
Pentium II: This is the Pentium Pro processor with the MMX instructions
added. (The Pentium III is essentially just a faster Pentium II.)

what about PentiumIV ?

So the Programming Instructions used for 80386 will work with pentium and unless we want some multimedia related Programs, I guess there is no need to learn about those?...