System on Chip Lecture-3: Computer Classes

• These are study notes for Dr. Haroon Waris' "System on Chip Lecture-3"

Traditional Classes of Computers

• Personal: General purpose, variety of software. Subject to cost/performance tradeoff.
• Server: Network based, high capacity, performance, reliability.
• Supercomputers: High-end scientific and engineering calculations; have the highest capability.
• Embedded: Hidden as components of systems with crucial power/performance/cost restrictions.

Embedded Computer

• A computer found inside another device.
• It runs a predetermined application or software collection.

Computer Components

• The five components include: input, output, memory, datapath, and control.
• These components are consistent across desktops, servers, and embedded systems.
• Input/output (I/O) includes user-interface devices, like displays, keyboards, and mice.
• Storage devices, like hard disks, CDs/DVDs, and flash memory are also components.
• Network adapters are used for communication with other computers.

"Analytical Engine"

• Created in (1837-1871)
• It was the first concept of a programmable general-purpose computer.
• Invented by Charles Babbage, known as the "Father of Computing".
• It could do calculations before being set to do so.
• Its components included the main components of a modern computer.
• The Mill represents the CPU and ALU. It had conditional branching.
• The Store represents the Memory. It had (1K 50-digit numbers).
• The Reader represents Input via Jacquard Punch Cards.
• The Printer represents Output in mathematical tables.
• Ada Lovelace wrote its first program, an algorithm to calculate Bernoulli numbers.

Turing Machine

• Described in 1936 by Alan Turing.
• The machine is capable of computing all computable problems.
• Made up of finite states, and an infinite tape (memory) of symbols
• It has a scanner that can read and write to the current position
• Turing completeness is the ability for a system of instructions to simulate a Turing machine.

Early Computers

• The ENIAC is often considered "the first computer," also called Electronically Programmable General Purpose Computer".
• It was the first electronic Turing Machine, but programming required rewiring hundreds of cables.
• It took days or weeks to program.
• With the EDVAC, Mauchly and Eckert came up with using instructions as another piece of data.
• Von Neumann wrote the nominal paper about the "stored-program".

Stored-Program Computers

• A Von Neumann Machine runs in a stored-program computer.
• Instructions are in binary, like data.
• Programs stored in memory, like data.
• The memory can be read and written when given an address.
• The program counter (PC) saves the current instruction address.
• Program flow is achieved by incrementing the PC or branching.
• Programs can operate on programs like compilers and linkers.
• Programs ship as files of binary numbers called "binaries".
• "Binary compatibility" allows compiled programs to work on different computers.

Microcoded Computers

• In early processor, ROM was cheaper and faster than RAM.
• Logic was expensive compared to ROM, and getting the control unit was hard.
• In 1958, Maurice Wilkes came up with microcoding.
• It implements the "microcoded” control unit with ROM to make it programmable.
• Microcode turns complex instructions into datapath control signals.
• It is part of the micro-architecture and not programmer-visible.
• It enables easier design, bug fixes, and support for new instructions (without changing datapath).
• Microcoded Computers do not benefit from µarch innovations, better compilers, reprogramming.
• First used to design the control unit of EDSAC-II.

CISC

• CISC stands for complex instruction set computers
• These commonly have a large variety of instructions.
• Instructions may perform complex tasks like string searching.
• They are very common for early computer architectures.

RISC

• RISC stands for reduced instruction set computers.
• They use fewer and simpler instructions.
• Most compiled code only used a few of the available CISC instructions.
• They use Load/Store instruction sets.
• Operations cannot be performed directly on memory locations, just registers.
• They're relatively straightforward to pipeline.
• Virtually all ISAs invented since the eighties are RISC.

Princeton/Harvard Architecture

• Von Neumann, also called Princeton Architecture shares a single memory space for instructions and data.
• This can either read an instruction or read/write data from/to memory which limits operating bandwidth.
• Harvard Architecture will use two different memory spaces for instructions and data.
• The CPU can concurrently read one instruction and access memory.
• RISC designs are common in this architecture to improve operating throughput.

The Computer Architecture Monopoly

• Thousands of architectures have been invented and used; the majority died off.
• The general purpose ISAs are Intel x86, ARM, and RISC-V.
• Intel x86 (a.k.a., AMD64) is a CISC architecture.
• It still dominates the laptop, desktop, and server markets.
• ARM is a formerly RISC architecture and dominates the embedded computing market.
• RISC-V is an open-source RISC architecture.
• Other ISAs survive as legacy or for application-specific reasons.