Introduction

The Hardware/ Software Interface Class

The hardware/ software interface
How does the h/w(0s and 1s, processor executing instructions) relate to the s/w (Go programs)?
Computing is about abstractions (but we can’t forget reality)
What are the abstractions that we use?
What do YOU need to know about them?
- When do they break down and you have to peek under the hood?
- What bugs can they cause and how do you find them?
Become a better programmer and begin to understand the important concepts that have evolved in building ever more complex computer systems.

All digital systems represnt everything as 0s and 1s
- The o and 1 are really two different voltage ranges in the electronics
Everything includes:
- Numbers - integers and floating point
- Character - the building blocks of strings
- Instructions - the directives to the CPU that make up a program
- Pointers - addresses of data objects stored away in memory
These encodings are stored throughout a computer system
- In registers, caches, memories, disks, etc
They all need addresses
- A way to find them
- Find a new place to put a new item
- Reclain the place in memory when data no longer needed

There is a big gap between how we thing about programs and data and the 0s and 1s of computers
Need languages to describe what we mean
Languages need to be translated one step at a time
- Word-by-word
- Phrase structure
- Grammar
We know Java/Go as a programming language
- Have to work our way down to the 0s and 1s of computers
- Try not to lose anything in translation!
- We’ll encounter Java/Go byte-code, C language, assembly language, and machine code (for the X86 family of CPU architectues)

How do computers orchestrate the many things they are doing - seemingly in parallel
What do we have to keep track of when we call a method, and then another, and then another, and so on
How do we know what to do upon “return”
How do we run multiple user programs and let them share a sigle computer and memory

program lifetime

Program lifetime illustration

The time required to execute a program depends on:
- The program.
- The compiler: what set of assember instructions it translates the program into.
- The instruction set architecture (ISA): what set of instructions it makes available to the compiler.
- The hardware implementation: how much time it takes to execute an instruction.

The ISA defines:
- The system’s state (e.g. registers, memory, program counter)
- The instructions the CPU can execute
- The effect that each of these instructions will have on the system state

Instructions
- What instructions are available? What do they do?
- How are they encoded? (eg 32bits, 64bits)
Registers
- How many registers are there?
- How wide are they?
Memory(addressing modes)
- How do you specify a memory location?

Processors that implement the x86 ISA completely dominate the server, desktop and laptop markets
Evolutionary design
- Backwards compatibility up until 8086, introduced in 1978
- Added more features as time goes on
Complex instruction set computer (CISC)
- Many different instructions with many different formats
  - But, only small subset encountered with Linux programs
- (as opposed to Reduced Instruction Set Computers (RISC), which use simpler instructions)

Name	Date	Transistors	MHz
8086	1978	29k	5-10

Name	Date	Transistors	MHz
386	1985	275k	16-33

Name	Date	Transistors	MHz
Pentium 4F	2005	230M	2800-3800

Intel Core i7

How about encoding a standard deck of playing cards?
52 cards in 4 suits
- How do we encode suits, face cards?
What operations do we want to make easy to implement?
- Which is the higher value card?
- Are they the same suit?

Two possible representation