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Hard drive access

How does a CPU manage to address remote memory locations on several hundred gigabyte bytes of a hard disk with registers and a data bus of only 32 bits.

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RAM is directly mapped to the processor address / data bus. There are no hard drives. They interact with the disk controller (IDE, SATA, SCSI, etc.). The disk controller copies data to / from RAM in smaller blocks, where the CPU works with it.

There are various addressing schemes for hard drives, such as LBA, CHS, etc., which themselves from time to time face restrictions.

Therefore, the processor only needs access to caches and RAM, since the hard drive itself is too slow for it. A 32-bit processor can simultaneously access 4 GB of memory, which is the limit of the size of physical memory in these systems. Therefore, the sequence

HDD-->RAM-->Caches-->Processor

Read this and this .

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Source: https://habr.com/ru/post/1478967/

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