1.7 Main memory(RAM) Addressing

✅ RAM

storage of open files and applications = processes

• process: open and running file and application

• RAM is divided into address

• addresses are numbered in hexadecimal
• the address at the user area the most top, is 0
• the address the the most bottom is F

Q_1: If the last address of the RAM is FFFFFFFFh, how many bits are there in this address?
A: each F has 4 bits internally, has 4 * 8 = 32 bits
- thus, this RAM is using 32 bits for the address
- thus, this RAM is using 32 bits for addressing(direcionar) the RAM

☑️ Capacity of RAM

• ⭐️ by looking at the last address, we can know the capacity of the RAM

• ⭐️ each F has 4 bits internally

• Following the computing principle, if the RAM has FFFFFFFFh 32 bits, RAM can have 2^32 combinations of address
• If in each address, I store 1 byte = 8 bits of information
• I can save up to 2^32 * 1 byte in my RAM
• more or less 4 * 1000 * 1000 * 1000 bytes
• 1000 = Kilo
• 1000 * 1000 = Mega
• 1000 * 1000 * 1000 = Giga
• so, 4 * Giga bytes
• in conclusion, if the last address of the RAM is FFFFFFFFh, this RAM has a total of 4 Giga Bytes

📌 hexadecimal

numbering system that groups bits by 4, starting by the right
> 1111 = 15 = F

• 1️⃣ divide bits by grouping them into 4, starting by the right
  • if the group is not complete, complete left with 0
• 2️⃣ then applies the weight rule to each group of 4
• 3️⃣ then changes the weight of 10 into the letter A
• 11 ➡️ B
• 12 ➡️ C
• 13 ➡️ D
• 14 ➡️ E
• 15 ➡️ F
• 4️⃣ add a h

address = 010101111111

1️⃣ divide into groups of 4, from the right
- 1111
- 0111
- 0101

2️⃣ apply weight
- 8421 /  8421 /  8421

- 1111 = 1 + 2 + 4 + 8 = 15
- 0111 = 1 + 2 + 4 = 7
- 0101 = 1 + 4 = 5

3️⃣ change weight into letter
- 15 = F
- 7
- 5

💡 result is 57F

4️⃣ always add h to say this address is hexadecimal
💡 result is 57Fh

address = 1110110

1️⃣ divide into groups of 4, from the right
if group is not complete, add 0 to the left
- 0111
- 0110

2️⃣ apply weight
- 0111 = 7
- 0110 = 6

3️⃣ change weight into letter
nothing to change
- 7
- 6

💡 result is 76

4️⃣ always add h to say this address is hexadecimal
💡 result is 76h

1110
weight = 14
💡 result is Eh

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