How is data retrieved from RAM?

Question

In C, each byte is individually addressable. Suppose an integer (say that uses 4 bytes) has an address 0xaddr(which is 32 bits, assuming we have a 32-bit processor with a 32-bit address bus and a 32-bit data bus) and assume that the value integer 0x12345678. Now, if I retrieve this value from memory, how does the processor do it? Does the processor 0xaddr(which is a 32-bit address) put on the address lines, and then it extracts 8-bit data, say 0x12. And then the processor will step 0xaddr+1along the address lines, and then extract another 8 bits of data 0x34, etc. For 4 bytes of an integer? Or 0xaddrdid the processor simply place and immediately read 4 bytes, thus using its full 32-bit data bus?

Answer 1

This is a well-known article in the GNU C library that describes memory access (especially on x86 - current PC systems). This is much more detailed than you might need.

The whole article is distributed in many parts:

• Introduction
• Processor cache
• Virtual memory
• NUMA Support
• Programmers
• Other programmers
• Performance
• Future
• Applications

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Answer 2

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