6.004 The Digital Abstraction

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The Digital Abstraction

Q: the physical representation of bits?

Then ask what is a good bit?

  • small
  • cheap
  • stable
  • easy and fast to manipulate, access/transform/combine/store/transmit

Industry selected to use voltage to represent information.
But the system need to tolerate errors.

Encode 1 bit with 0 or 1.

Digitalize voltage with buffer.

Combinational logic

Stateless machine

Sequential logic

Circuits that include both combinational logic and memory components are called sequential logic.

Finite state machine

Instruction Set Architectures

An instruction is the fundamental unit of work, it includes: opcode to be performed and operands, destination for the result.

ISA, is a contract between software and hardware. ISA is the first abstraction layer that describes what CPU can do but hides how CPU do it.

Beta: a RISC, reduced instruction set computer.

Assembly

A human readable ISA+

Compiler

High level languages. Two basic execution logic: interpretation and complilation.

Front end + Back end.

Procedures, abstraction by high level languages

Memory tech

Everything is cache of something else..