Computer Memory: An Introduction to RAM

In the simple terms, computer memory is an electronic mechanism

that has the ability to store and retrieve data.

The smallest amount of data that can be stored is 1 bit, which

can be represented by either a 1 or a 0 in memory.

When you put 4 bits together, it is called a nibble, which can represent values from 0000 to 1111. There are exactly 16 binary

values, ranging from 0 to 15, in decimal format.

When you put two nibbles or 8 bits together, you get a byte, which can represent values from 0 to (2^8 – 1), or 0–255 decimal.

When you put 2 bytes together, you get a word, which can represent values from 0 to

(2^16 – 1), or 0–65,535 in decimal.

Continuing to piece data together, if you put two

words together, you get a double word or “DWORD,”

which can represent values from 0–4,294,967,295 in decimal.

There are many types of computer memory;

we will focus on random access memory

(RAM).

Random Access Memory (RAM)

In RAM, any piece of stored data can be retrieved at any time—thus, the term “random

access.” However, RAM is volatile, meaning that when the computer is turned off, all data

is lost from RAM. When discussing modern Intel-based products (x86), the memory is

32-bit addressable, meaning that the address bus the processor uses to select a particular

memory address is 32 bits wide. Therefore, the most memory that can be addressed in

an x86 processor is 4,294,967,295 bytes.

Endian

As Danny Cohen summarized Swift’s Gulliver’s Travels in 1980:

“Gulliver finds out that there is a law, proclaimed by the grandfather of the

present ruler, requiring all citizens of Lilliput to break their eggs only at the

little ends. Of course, all those citizens who broke their eggs at the big ends

were angered by the proclamation. Civil war broke out between the Little-

Endians and the Big-Endians, resulting in the Big-Endians taking refuge on

a nearby island, the kingdom of Blefuscu…”

He went on to describe a holy war that broke out between the two sides.

The point of his paper was to describe the two schools of thought when writing data into memory.

Some feel that the high-order bytes should be written first (“little-endian”), while others think

the low-order bytes should be written first (“big-endian”).

It really depends on the hardware you are using as to the difference. For example, Intel-based processors use the little-endian method, whereas Motorola-based processors use big-endian.

In the simple terms, computer memory is an electronic mechanism

that has the ability to store and retrieve data.

The smallest amount of data that can be stored is 1 bit, which

can be represented by either a 1 or a 0 in memory.

When you put 4 bits together, it is called a nibble, which can represent values from 0000 to 1111. There are exactly 16 binary

values, ranging from 0 to 15, in decimal format.

When you put two nibbles or 8 bits together, you get a byte, which can represent values from 0 to (2^8 – 1), or 0–255 decimal.

When you put 2 bytes together, you get a word, which can represent values from 0 to

(2^16 – 1), or 0–65,535 in decimal.

Continuing to piece data together, if you put two

words together, you get a double word or “DWORD,”

which can represent values from 0–4,294,967,295 in decimal.

There are many types of computer memory;

we will focus on random access memory

(RAM).

Random Access Memory (RAM)

In RAM, any piece of stored data can be retrieved at any time—thus, the term “random

access.” However, RAM is volatile, meaning that when the computer is turned off, all data

is lost from RAM. When discussing modern Intel-based products (x86), the memory is

32-bit addressable, meaning that the address bus the processor uses to select a particular

memory address is 32 bits wide. Therefore, the most memory that can be addressed in

an x86 processor is 4,294,967,295 bytes.

Endian

As Danny Cohen summarized Swift’s Gulliver’s Travels in 1980:

“Gulliver finds out that there is a law, proclaimed by the grandfather of the

present ruler, requiring all citizens of Lilliput to break their eggs only at the

little ends. Of course, all those citizens who broke their eggs at the big ends

were angered by the proclamation. Civil war broke out between the Little-

Endians and the Big-Endians, resulting in the Big-Endians taking refuge on

a nearby island, the kingdom of Blefuscu…”

He went on to describe a holy war that broke out between the two sides.

The point of his paper was to describe the two schools of thought when writing data into memory.

Some feel that the high-order bytes should be written first (“little-endian”), while others think

the low-order bytes should be written first (“big-endian”).

It really depends on the hardware you are using as to the difference. For example, Intel-based processors use the little-endian method, whereas Motorola-based processors use big-endian.




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