diff --git a/CMakeLists.txt b/CMakeLists.txt
index b37e7f4..ab108fa 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -36,4 +36,4 @@ add_executable(ComSquare
     sources/Exceptions/NotImplementedException.hpp
     sources/APU/APU.hpp
     sources/APU/APU.cpp
-        sources/Exceptions/InvalidAddress.hpp sources/Exceptions/InvalidRom.hpp sources/Models/Ints.hpp sources/Models/Ints.hpp)
+        sources/Exceptions/InvalidAddress.hpp sources/Exceptions/InvalidRom.hpp sources/Models/Ints.hpp sources/Models/Ints.hpp sources/Ram/Ram.cpp sources/Ram/Ram.hpp)
diff --git a/sources/CPU/CPU.cpp b/sources/CPU/CPU.cpp
index 4041c34..f2b6358 100644
--- a/sources/CPU/CPU.cpp
+++ b/sources/CPU/CPU.cpp
@@ -44,6 +44,8 @@ namespace ComSquare::CPU
 			return this->_internalRegisters.mdmaen;
 		case 0xC:
 			return this->_internalRegisters.hdmaen;
+		case 0xD:
+			return this->_internalRegisters.memsel;
 		case 0x10:
 			return this->_internalRegisters.rdnmi;
 		case 0x11:
@@ -123,6 +125,9 @@ namespace ComSquare::CPU
 		case 0xC:
 			this->_internalRegisters.hdmaen = data;
 			break;
+		case 0xD:
+			this->_internalRegisters.memsel = data;
+			break;
 		case 0x10:
 			this->_internalRegisters.rdnmi = data;
 			break;
@@ -178,7 +183,11 @@ namespace ComSquare::CPU
 
 	int CPU::update()
 	{
-		throw NotImplementedException();
+		int cycles = 0;
+
+		for (int i = 0; i < 0xFF; i++)
+			cycles += this->executeInstruction();
+		return cycles;
 	}
 
 	int CPU::executeInstruction()
diff --git a/sources/Memory/IMemory.hpp b/sources/Memory/IMemory.hpp
index 4ae25ed..990807b 100644
--- a/sources/Memory/IMemory.hpp
+++ b/sources/Memory/IMemory.hpp
@@ -12,15 +12,35 @@
 
 namespace ComSquare
 {
+	//! @brief Common interface implemented by all components mapping memory.
 	class IMemory {
 	private:
+		//! @brief The starting address mapped to this component.
 		uint24_t _start = 0;
+		//! @brief The last continuous address mapped to this components. For shadows, see the MemoryShadow class.
 		uint24_t _end = 0;
 	public:
+		//! @brief Read data from the component.
+		//! @param addr The local address to read from (0x0 should refer to the first byte of this component).
+		//! @throw This function should thrown an InvalidAddress for address that are not mapped to the component.
+		//! @return Return the data at the address given as parameter.
 		virtual uint8_t read(uint24_t addr) = 0;
+		//! @brief Write data to this component.
+		//! @param addr The local address to write data (0x0 should refer to the first byte of this component).
+		//! @param data The new data to write.
+		//! @throw This function should thrown an InvalidAddress for address that are not mapped to the component.
 		virtual void write(uint24_t addr, uint8_t data) = 0;
+		//! @brief Change starting and ending points of this mapped memory.
+		//! @param start The first address mapped to this component.
+		//! @param end The last address mapped to this component.
+		//! @warning The start/end address should be a continuous range. You can't map address 0x0 and 0x2 but not 0x1. To do that, use two IMemory.
 		void setMemoryRegion(uint24_t start, uint24_t end);
+		//! @brief Return true if this component has mapped the address.
+		//! @param addr The address to check.
+		//! @return True if this address is mapped to the component. False otherwise.
 		bool hasMemoryAt(uint24_t addr);
+		//! @brief Get the first address mapped to this component.
+		//! @return the _start value.
 		uint24_t getStart();
 	};
 };
diff --git a/sources/Memory/MemoryBus.cpp b/sources/Memory/MemoryBus.cpp
index 1350b6a..bf9f1dc 100644
--- a/sources/Memory/MemoryBus.cpp
+++ b/sources/Memory/MemoryBus.cpp
@@ -10,10 +10,13 @@ namespace ComSquare
 {
 	std::shared_ptr<IMemory> MemoryBus::getAccessor(uint24_t addr)
 	{
-		return *std::find_if(this->_memoryAccessors.begin(), this->_memoryAccessors.end(), [addr](std::shared_ptr<IMemory> &accessor)
+		auto it = std::find_if(this->_memoryAccessors.begin(), this->_memoryAccessors.end(), [addr](std::shared_ptr<IMemory> &accessor)
 		{
 			return accessor->hasMemoryAt(addr);
 		});
+		if (it == this->_memoryAccessors.end())
+			return nullptr;
+		return *it;
 	}
 
 	uint8_t MemoryBus::read(uint24_t addr)
diff --git a/sources/Memory/MemoryBus.hpp b/sources/Memory/MemoryBus.hpp
index 70ae1ff..fa5b097 100644
--- a/sources/Memory/MemoryBus.hpp
+++ b/sources/Memory/MemoryBus.hpp
@@ -12,13 +12,25 @@
 
 namespace ComSquare
 {
+	//! @brief The memory bus is the component responsible of mapping addresses to components address and transmitting the data.
 	class MemoryBus {
 	private:
+		//! @brief The list of components registered inside the bus. Every components that can read/write to a public address should be in this vector.
 		std::vector<std::shared_ptr<IMemory>> _memoryAccessors;
+		//! @brief Helper function to get the components that is responsible of read/write at an address.
+		//! @param addr The address you want to look for.
+		//! @return The components responsible for the address param or nullptr if none was found.
 		std::shared_ptr<IMemory> getAccessor(uint24_t addr);
-		uint8_t _openbus;
+		//! @brief The last value read via the memory bus.
+		uint8_t _openbus = 0;
 	public:
+		//! @brief Read data at a global address.
+		//! @param addr The address to read from.
+		//! @return The value that the component returned for this address. If the address was mapped to ram, it simply returned the value. If the address was mapped to a register the component returned the register.
 		uint8_t read(uint24_t addr);
+		//! @brief Write a data to a global address.
+		//! @param addr The address to write to.
+		//! @param data The data to write.
 		void write(uint24_t addr, uint8_t data);
 	};
 }
diff --git a/sources/Ram/Ram.cpp b/sources/Ram/Ram.cpp
new file mode 100644
index 0000000..726e167
--- /dev/null
+++ b/sources/Ram/Ram.cpp
@@ -0,0 +1,29 @@
+//
+// Created by anonymus-raccoon on 1/28/20.
+//
+
+#include "Ram.hpp"
+#include "../Exceptions/InvalidAddress.hpp"
+
+namespace ComSquare::Ram
+{
+	Ram::Ram(size_t size)
+		: _size(size)
+	{
+		this->_data = new uint8_t[size];
+	}
+
+	uint8_t Ram::read(uint24_t addr)
+	{
+		if (addr >= this->_size)
+			throw InvalidAddress("Ram read", addr);
+		return this->_data[addr];
+	}
+
+	void Ram::write(uint24_t addr, uint8_t data)
+	{
+		if (addr >= this->_size)
+			throw InvalidAddress("Ram write", addr);
+		this->_data[addr] = data;
+	}
+}
diff --git a/sources/Ram/Ram.hpp b/sources/Ram/Ram.hpp
new file mode 100644
index 0000000..b884c08
--- /dev/null
+++ b/sources/Ram/Ram.hpp
@@ -0,0 +1,34 @@
+//
+// Created by anonymus-raccoon on 1/28/20.
+//
+
+#ifndef COMSQUARE_RAM_HPP
+#define COMSQUARE_RAM_HPP
+
+#include "../Memory/IMemory.hpp"
+
+namespace ComSquare::Ram
+{
+	class Ram : IMemory {
+	private:
+		//! @brief The ram. (Can be used for WRam, SRam, VRam etc)
+		uint8_t *_data;
+		//! @brief The size of the ram.
+		size_t _size;
+	public:
+		//! @brief Load a rom from it's path.
+		explicit Ram(size_t size);
+		//! @brief Read from the ram.
+		//! @param addr The address to read from. The address 0x0 should refer to the first byte of this ram.
+		//! @throw InvalidAddress will be thrown if the address is more than the size of the ram.
+		//! @return Return the data at the address.
+		uint8_t read(uint24_t addr) override;
+		//! @brief Write data to the ram.
+		//! @param addr The address to write to. The address 0x0 should refer to the first byte of this ram.
+		//! @param data The data to write.
+		//! @throw InvalidAddress will be thrown if the address is more than the size of the ram.
+		void write(uint24_t addr, uint8_t data) override;
+	};
+}
+
+#endif //COMSQUARE_RAM_HPP