Tutorials/Redstone computers

=Preface= This article examines the design and implementation of computing systems within the world of Minecraft.

=Computing systems= Computers facilitate the implementation of ideas which are communicated from humans through programming.

All computer systems have accessible memory and at-least one processing unit, During operation processing units execute instructions stored in the computers memory.

=Planning a Redstone computer= When designing a computer ( Redstone or otherwise ) key design decisions that will affect the organization, size and performance of your prospective computer should be made concretely prior to the construction of specific components.

Some things to consider:


 * Execution model ( The computer's organization of memory relating to program storage and execution )
 * Word-size ( The size of the information blocks which your computer will operate on )
 * Instruction Set ( That set of operations which your computer will execute )

Having a selection decided upon will provide strong guidance during the design of various components in your computer.

Execution Model
The technique of storing blocks of instructions called programs within memory is what allows computers to perform such a variety of tasks.

The apparatus employed by a computer for storing and retrieving these programs is the computers Execution Model.

Two of the world's most successful Execution Models, Harvard and von Neumann, run on nearly 100% of the computers available today.

Harvard
The Harvard architecture physically separates the apparatus for retrieving the instructions which makeup an active program from that of the data access apparatus which the program accesses during execution.

Programs written for computers employing a Harvard architecture may perform up-to %100 faster for tasks which access the main memory bus. Note however that certain memory circuitry is necessarily larger for those who select a Harvard architecture.

von Neumann
The von Neumann architecture uses a two-step process to execute instructions. First, memory containing the next instruction is loaded, then the new instruction just loaded is allowed to access this same memory as it executes, using a single memory for both program and data facilitates Meta-Programming technology like compilers and Self modifying Code.

The von Neumann architecture was the first proposed model of computation and almost all real-world computers are von Neumann in nature.

Word sizes
Word-size is a primary factor in a computer's physical size.

In Minecraft, machines from 1-bit all the way up-to 32-bits have been successfully constructed.

Common word-size combinations :

Data-Word
The amount of information a computer can manipulate at any particular time is representative of the computer's Data Word-size.

In Digital Binary, the computer's Data-Word size ( measured in bits ) is equal to the width of or number of channels in the computers main bus.

Data-Words commonly represent integers, or whole numbers encoded as patterns of binary digits.

The maximum sized number representable by a Binary encoded integer is given by 2 ^ Data-Word width in bits.

Some common Integer data sizes are:

Data-Word size also governs the maximum size of numbers which can be processed by a computers ALU (Arithmetic and Logic Unit).

Instruction-Word
The amount of data a computer needs in order to complete one single instruction is representative of a computers Instruction Word-size.

The Instruction-Word size of a computer is generally a multiple of its Data-Word size, This helps minimize memory misalignment while retrieving instructions during program execution.

=Designing a Computer=

Arithmetic Logic Unit


The ALU is one of the most important components in a computer, both in real life and in Minecraft. First, you must choose the functions you want to be able to achieve. Most often, those are addition,  substraction and a set of logic options such as AND, OR,  NAND and the likes. You must then build the unit with all the logic gates and math functions you want and a way to choose which one's output to display.

Program Memory


Program memory is most often used to perform a series of task remotely (if you use a clock or put delay between each command) or by user control. One of the simplest and most efficient design is the one in the picture, which may or may not be coupled with a decoder. It can be enlarged easily, which is another advantage.

Clock


Clocks are used to synchronize components or to time them. In most (Minecraft) cases, it is possible to avoid the use of one but sometimes it is necessary for the computer's functioning. It can be either made from redstone torches in basically a line/circle of NOT gates (an odd number is recommended or your output will have to be NOT'ed), or from repeaters, as in the picture above.