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1. 1. Addressability Memory 11110011 Address 00000000 00000001 00000010 00000011 00000100 00000101 00000110 00000111 00001000 00001001 Each memory location has to have an address Each address is a unique identifier for that specific memory location The way in which the computer identifies memory locations is known as addressability
2. 2. Memory locations Memory Address 0 1 The width of the address bus determines how many memory locations can be addressed A 1 bit address bus can access 2 memory locations Processor 1 Bit Address Bus
3. 3. Memory locations Memory Address 10 11 The width of the address bus determines how many memory locations can be addressed A 2 bit address bus can access 4 memory locations Processor 00 012 Bit Address Bus
4. 4. Memory locations Memory Address 110 111 The width of the address bus determines how many memory locations can be addressed A 3 bit address bus can access 8 memory locations Processor 100 101 010 011 000 0013 Bit Address Bus
5. 5. Memory locations How many memory locations could a computer with an 8 bit address bus access? How many memory locations could a computer with an 16 bit address bus access? How many memory locations could a computer with an 32 bit address bus access?
6. 6. Memory locations How many memory locations could a computer with an 8 bit address bus access? 28 = 256 memory locations How many memory locations could a computer with an 16 bit address bus access? How many memory locations could a computer with an 32 bit address bus access?
7. 7. Memory locations How many memory locations could a computer with an 8 bit address bus access? 28 = 256 memory locations How many memory locations could a computer with an 16 bit address bus access? 216 = 65,536 memory locations How many memory locations could a computer with an 32 bit address bus access?
8. 8. Memory locations How many memory locations could a computer with an 8 bit address bus access? 28 = 256 memory locations How many memory locations could a computer with an 16 bit address bus access? 216 = 65,536 memory locations How many memory locations could a computer with an 32 bit address bus access? 232 = 4,294,967,296 memory locations
9. 9. Calculating addressable memory If a computer has an 3 bit address bus, we know that it has 23 = 8 memory locations But how much actual memory is that? Memory Address 110 111 Processor 100 101 010 011 000 0013 Bit Address Bus
10. 10. Calculating addressable memory In order to answer that question, we need to know how many bits can be stored in each memory location. This is determined by the width of the data bus. Memory Address 110 111 Processor 100 101 010 011 000 0013 Bit Address Bus Data Bus
11. 11. Calculating addressable memory A computer with a data bus 2 bits wide would store 2 bits in each memory location. Memory Address 110 111 Processor 100 101 00 00 11 00 10 11 01 01 010 011 000 0013 Bit Address Bus 2 Bit Data Bus
12. 12. Calculating addressable memory Therefore, a computer with a 2 bit data bus and a 3 bit address bus would have an addressable memory of 8 x 2 = 16 bits = 2 bytes Memory Address 110 111 Processor 100 101 00 00 11 00 10 11 01 01 010 011 000 0013 Bit Address Bus 2 Bit Data Bus
13. 13. Calculating addressable memory Total addressable memory = the number of storage locations x the size of each storage location
14. 14. Calculating addressable memory Example: Calculate the total addressable memory of a computer with a 16 bit address bus and an 8 bit data bus.
15. 15. Calculating addressable memory Example: Calculate the total addressable memory of a computer with a 16 bit address bus and an 8 bit data bus. addressable memory = Number of storage locations x the size of each location = 216 bits x 8 bits
16. 16. Calculating addressable memory Example: Calculate the total addressable memory of a computer with a 16 bit address bus and an 8 bit data bus. addressable memory = Number of storage locations x the size of each location = 216 x 8 bits = 65536 x 1 byte = 65536 bytes = 64 kb
17. 17. Credits Higher Computing – Computer Structure – Addressability Produced by M. Cunningham for the City of Edinburgh Council 2010 All images licenced under Creative Commons 3.0 • Metropolitan Vickers, Trafford Park stationery by sludgegulper on Flickr • Calculator Dreams by Keith Ramsey (RambergMediaImages on Flickr)