CODEWITHSUNDEEP
memorymemory-managementoperating-system
linonymous
linonymous

Reputation: 141

Who brings a program from Secondary memory(Hard Disk) to Primary Memory(RAM) for execution?

In the book "Operating System Concept by SILBERSCHATZ, GALVIN & GAGNE", they've mentioned that,

Main Memory(Primary memory) and the registers built into the processor itself are the only storage that CPU can access directly

This statement has caused a lot of confusion. If CPU can not access Secondary Memory, then how does it fetch a program from Secondary Memory?

Upvotes: 1

Views: 4701

Answers (1)

amaneureka
amaneureka

Reputation: 1150

CPU can't access Secondary memory directly doesn't mean It can't access it anyway. when System is booted, BIOS inbuilt program (in ROM) copy boot loader (from secondary bootable device) to RAM's memory and ask cpu to continue execution from that particular address. Once CPU starts executing Boot loader, Boot loader calls necessary function to read from disk (secondary storage) and copy your OS kernel image into memory. transfer of data is done through I/O ports.
You have your kernel image into memory, and thus boot loader ask cpu to jump to kernel's entry point. You have your kernel starting up this point. Kernel setup OS environment, load up necessary drivers (including disk/cd-rom driver). After this point, It is up to OS disk driver that It performs I/O port operation or DMA access to load up data from secondary storage. Generally DMA is preferred because It does not involve CPU for polling up data from device, but It is little difficult to code.
I hope I cleared your doubt :)

Upvotes: 2

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