As a CPU needs to communicate with the various memory and input-output devices (I/O) as we know data between the processor and these devices flow with the help of the system bus. There are three ways in which system bus can be allotted to them :
- Separate set of address, control and data bus to I/O and memory.
- Have common bus (data and address) for I/O and memory but separate control lines.
- Have common bus (data, address, and control) for I/O and memory.
In first case it is simple because both have different set of address space and instruction but require more buses.
Isolated I/O –
Then we have Isolated I/O in which we Have common bus(data and address) for I/O and memory but separate read and write control lines for I/O. So when CPU decode instruction then if data is for I/O then it places the address on the address line and set I/O read or write control line on due to which data transfer occurs between CPU and I/O. As the address space of memory and I/O is isolated and the name is so. The address for I/O here is called ports. Here we have different read-write instruction for both I/O and memory.
Memory Mapped I/O –
In this case every bus in common due to which the same set of instructions work for memory and I/O. Hence we manipulate I/O same as memory and both have same address space, due to which addressing capability of memory become less because some part is occupied by the I/O.
Differences between memory mapped I/O and isolated I/O –
|Isolated I/O||Memory Mapped I/O|
|Memory and I/O have seperate address space||Both have same address space|
|All address can be used by the memory||Due to addition of I/O addressable memory become less for memory|
|Separate instruction control read and write operation in I/O and Memory||Same instructions can control both I/O and Memory|
|In this I/O address are called ports.||Normal memory address are for both|
|More efficient due to seperate buses||Lesser efficient|
|Larger in size due to more buses||Smaller in size|
|It is complex due to separate separate logic is used to control both.||Simpler logic is used as I/O is also treated as memory only.|
- Introduction to memory and memory units
- Difference between Byte Addressable Memory and Word Addressable Memory
- Secondary Memory
- 2D and 2.5D Memory organization
- Types of computer memory (RAM and ROM)
- Computer Organization | Memory Banking
- Memory Segmentation in 8086 Microprocessor
- How the negative numbers are stored in memory?
- Computer Organisation | One bit memory cell
- Computer Organization | Cache Memory
- Read-Only Memory (ROM) | Classification and Programming
- Different Types of RAM (Random Access Memory )
- MCQ on Memory allocation and compilation process
- Operating System | Overlays in Memory Management
- Computer Organization | Read and Write operations in memory
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