# Bits, bytes, and computer memory

[Programming guides](README.md)

Computers represent information using patterns of **bits**. A bit has two possible values, usually written as 0 and 1. A group of eight bits is called a **byte**.

Bits can represent numbers, text, pictures, and sounds when a program knows how to interpret the pattern. The pattern alone does not explain what it means.

## Make number cards

Imagine four cards labelled 8, 4, 2, and 1. Turn a card face up for a bit of 1 and face down for a bit of 0. Add the visible values.

The pattern 1101 gives 8 + 4 + 0 + 1, which is thirteen. This way of writing numbers is called **binary**. Eight bits give 256 different patterns; those patterns can represent the whole numbers 0 through 255. That does not mean every Pliro number is stored in one byte.

## Read a bit pattern

Pliro does not need a special binary literal for this experiment. We use ordinary numbers in a list.

```pliro
# language: en
let bits = [1, 1, 0, 1]
let value = 0
for bit in bits:
    set value = value * 2 + bit
say value
```

Multiplying by two makes room for the next binary digit. Adding the bit puts that digit in place. After each round, the running values are 1, 3, 6, and 13.

## Predict, then run

Which ordinary number does 1101 represent?

```text
13
```

## Your challenge

Try the pattern `[1, 0, 1]`, using the cards 4, 2, and 1. Predict its value first. Only put zeros and ones in the list; other numbers would not describe bits.

## Memory and saving

Working memory, often called **RAM**, is like a desk for things a running program is using. Saved storage is more like a cupboard that can keep a file after the program closes. Saving the source code does not automatically save its current score.

## A common mistake

One visible character is not always one byte. Pliro source text uses [UTF-8](../concepts/utf-8.md), where different characters can use different numbers of bytes. `length` counts text code points, not file bytes. You can learn programming without calculating the byte size of every value.

## KiB and MiB: counting larger amounts

A **KiB** (kibibyte) is 1,024 bytes. A **MiB** (mebibyte) is 1,024 KiB, or 1,048,576 bytes. Pliro's storage limits use these units. The decimal labels **kB** and **MB** mean 1,000 and 1,000,000 bytes. Read the label instead of assuming every “kilo” means the same count.

A 64 KiB limit is a byte limit. With [UTF-8](../concepts/utf-8.md), different text can use different byte counts even when it has the same number of code points. Stored [JSON](../concepts/json.md) also includes its punctuation and field names.


## Where next?

[Numbers](../syntax/number.md) · [Text files](../syntax/encoding.md) · [Saving data](storage.md)