Computer Programs #

A Computer Program is simply just a laundry list of things to check and do.

A computer program will perform each step in sequence until it reaches the end of the list.

Instructions #

A computer only understands a finite number of operations or instructions.

A computer performs operations like arithmetic, logic, and data movement.

Registers & Memory #

A computer contains storage spaces that it can use to store values and context.

Registers are storage spaces located within a CPU which it uses to rapidly store values and context for a computation.

Memory on the other hand is an auxiliary storage space that is a lot less slower than registers but is fast enough for storing large runtime data capacity.

Addresses #

Addresses are unique locations that a computer instruction or storage space uses to be identified with.

Program Counter #

A Program Counter is a unit within a CPU that keeps the address of the next instruction to be performed.

Stack #

A stack is a data structure and a unit within a CPU that stores values and are stored and accessed using push and pop respectively at the end of the list.

Number Systems used in Computing #

Binary #

Binary is the number system that is used in computing and contains a value with a sequence of $0$'s or $1$'s which is called a bit.

Computers often uses groups of $8$-bit values or a byte which can represent at most $2^{8}$ unique values.

Hexadecimal #

Hexadecimal or hex is a numbering system that uses a base of $16$. This number system is often used to simply represent half a byte (or $4$-bits) of data.

This system goes from $0$ to $9$ then $A$ to $F$, totalling of $16$ unique values.

Since this can represent $4$-bits of data, in order to represent a $byte$, two hex values are needed to represent it.

For example:

Switches and Transistors #

Switches #

A switch in general is a mechanism that can store a bit $1$ (on) or $0$ (off).

There are mechanical switches which requires mechanical motion (ie. requires human intervention) to turn on or off and also electrical switches which requires electricity to turn on or off.

Transistors #

A transistor is an electrical switch which can be aggregated into a circuit or a closed network of electrical components to build a memory unit.

Reading or Writing from Memory #

The CPU and Memory communicate via the Memory's address line and both of their data lines connected to each other.

Reading #

When a CPU wants to read data from Memory, it sends it an address to the Memory's address line. The Memory, upon retrieving the data from the requested address space, puts the data into the interconnected data line of the CPU and Memory. Afterwards, reads the data content from its data line.

Writing #

In order for the CPU to write to Memory, it first populates its data line with the data it needs to write into Memory, then makes a request to Memory which address space it should be put into in the Memory's address line. Upon successfully retrieving the address space, The Memory writes (or overwites) the address space by reading from the data line.

The Data Bus #

The data bus is a communication system within a computer that transfers data between several computer components.

There are two types of data buses:

1. Memory Bus
2. I/O Bus

Memory Bus #

The memory bus allows CPU and Main Memory to transfer data between each other.

I/O Bus #

The I/O bus allows peripheral devices to transfer data between them and the CPU and Main Memory.

Computer Architecture #

A computer architecture defines the set of machine instructions, registers, data type and format, and how they will work together in order to process information.