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Why is it important that all data and instructions are in RAM in order to be processed?

For instance, why not just use a storage device like a hard disk to hold the data?

4 Answers

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  • 1 decade ago
    Favorite Answer

    Executing instructions aren't even stored in ram, they're stored in very expensive, very fast cache memory in the processor, the 2MB (or less!) in the processor account for a large part of the hardware costs. If the machine were made entirely with the cache, it would cost about $300,000.

    A hard drive is orders of magnitude slower than any disk drive. Plus, ram is solid state, ie no moving parts. When the computer goes into power saving mode, it stops spinning the CD-like platterrs and so you have to wait for all kinds of things, could be up to 7 seconds for a read, versus RAM at LESS THAN 100 nanoseconds for every operation. That's like 10 million times faster.

  • S
    Lv 4
    1 decade ago

    Main reason: performance. On a typical 32-bit architecture, each instruction is 4 bytes long. If you have a 3 GHz computer, it's processing 3x10^9 instructions a second. That's 11.18 gigabytes of instructions being transferred per second! Modern hard drives would be hard-pressed to provide a sustained transfer rate of even 100 MB/s. Therefore computer engineers decided it was a good idea to use RAM which has very fast accesss but not as much capacity to hold the instructions being executed. In practice, rarely does one encounter a program that does not fit into RAM. RAM nowadays have transfer rates around 3 GB/s.

  • 1 decade ago

    I'm not sure if instructions are in ram, but even if they were, it would be important for the purpose of speed and performance. If ram didn't exist, then data would have to be fetched on the harddrive, which would take for ever if you had allot of data to read.

  • Anonymous
    1 decade ago

    Because that would be retarded amounts of slow. RAM is easily 100 times faster to read/write than the hard disk.

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