1. Memory
A+ Chapter 5
Memory

2. Types of Memory
ROM – Read-Only Memory. This memory is also know as non-volatile memory. When the computer is shut off this type of memory is not lost. RAM – Random Access Memory. This is memory that is used by the CPU to store data. When we talk about computer memory we are talking about RAM!

3. The Memory Chip
Each character is called a BIT (Binary digIT). If you think of it as a light bulb it is either on or off.
BITs are arrayed in series of 8. Eight BITs in an array is called a Byte.
On the picture to the left the top byte shows the eight BITS numbered from 0 to 7.
Notice a short integer uses 2 bytes. Two bytes is called a word.
The long integer uses a double-word!
A half-byte is called a nibble.

4. Do the Math!
We represent memory using zeros and ones. The number would represent the decimal value is written in binary or base 2. Just as 13 in decimal represents 1-10 and 3-1’s represents 1-8, 1-4 and = 23, 4 = 22, 1 = 20,
In one byte of information we have: 27, 26, 25, 24, 23, 22, 21, 20. These represent the place value of either a zero or a one in the byte.
27= 128, 26= 64, 25= 32, 24= 16, 23= 8, 22= 4, 21= 2, 20= 1
So the binary number = =147 decimal
This is typically written as = (Although we don’t show the base 10 in decimal since we use it all the time)

5. Try these….
Convert each of the following binary numbers into decimal numbers:

6. Convert Decimal to Binary
To convert a decimal number to binary you do repeated division by 2. The remainder of the division is the binary number (only use the remainders). Keep dividing whatever you get for a whole number until you get to zero.
Or do repeated subtraction of the powers of 2. Each time you can do it place a 1 in the binary digit. Each time it isn’t possible place a zero in the binary digit. See the figure on the right 

7. Try these…
Convert these decimal numbers to binary. 12 56 88
127
304

8. RAM (Memory)
RAM (random access memory) is the place in a computer where the operating system, application programs, and data in current use are kept so that they can be quickly reached by the computer's processor.

9. Types RAM
The two most common types of RAM used in desktop computers today are DDR2 and DDR3. DDR is Dual Date Rate.
RAM can be listed using two different names. For example, DDR800 is also called PC The DDR number (800) is multiplied by 8 to calculate the PC (6400) number. 8 x 800 = 6400
Notebook computers use SODIMMS (Small Outline DIMMS) which take up less space than desktop memory.

10. Dual Channel RAM
Dual channel RAM allows the bandwidth between the memory and the memory controller to be doubled when compatible memory is installed on a dual channel motherboard.
Dual channel memory banks are normally color coded and require memory to be installed in both slots.

11. Compatibility
The choice of RAM is determined by the types of RAM which are compatible with the motherboard.
A motherboard designed specifically to use DDR RAM will not accept DDR2 RAM.
It is important to closely examine motherboard specifications for CPU and RAM before making a purchase.

12. Capacity
Different operating systems can address various amounts of RAM.
The majority of 32 bit versions of modern Microsoft Windows operating systems can address up to 4GB of RAM.
64 bit versions of Microsoft Windows operating systems can address 8GB or more of RAM depending on the specific edition.

13. Installation
As with other electronic components, always take steps to prevent electrostatic discharge (ESD) from damaging the RAM and motherboard.
Antistatic wrist straps and antistatic mats help to prevent ESD when installing components.