January 2016 Archive


Stable Storage
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Stable Storage

As we know, disks sometimes make errors. Good sectors can suddenly turn into bad sectors. Whole drives can stop functioning suddenly. RAIDs protect against a few sectors going bad or even a drive falling out. On the other hand, they do not protect against write errors laying

CLOCKS
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CLOCKS

Clocks (also called timers) are necessary to the operation of any multiprogrammed system for a variety of reasons. They keep the time of day and prevent one process from monopolizing the CPU, among other things. The clock software can take the form of a device driver, even

Clock Software
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Clock Software

All the clock hardware generate interrupts at known intervals. Everything else involving time must be done by the software, the clock driver. The exact duties of the clock driver vary among operating systems, but generally include most of the following:

Soft Timers
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Soft Timers

Nearly all computers have a second programmable clock that can be set to cause timer interrupts at whatever rate a program needs. This timer is in addition to the main system timer whose functions were described in previous post. As long as the interrupt frequency is low, there

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