April 2013 Archive


Ontogeny Recapitulates Phylogeny
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Ontogeny Recapitulates Phylogeny

After Charles Darwin's book on the origin of the species was published, the German zoologist Ernst Haeckel stated that "ontogeny recapitulates phylogeny". By this he meant that the

Large Memories
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Large Memories

Let us now study some historical developments in hardware and how they have affected software over and over again. The first mainframes had limited memory. A fully loaded IBM

Protection Hardware
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Protection Hardware

Early mainframes, like the IBM 7090/7094, had no protection hardware, so they just ran one program at a time. A buggy program could wipe out the operating system and easily crash

Hard Disks
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Hard Disks

Initial mainframes were mostly magnetic-tape based. They would read in a program from tape, compile it, run it, and write the results back to another tape. There were no disks and

Virtual Memory
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Virtual Memory

Virtual memory (discussed in "MEMORY MANAGEMENT"), gives the ability to run programs larger than the machine's physical memory by moving pieces back and forth between RAM

SYSTEM CALLS
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SYSTEM CALLS

Operating systems have two major jobs: providing abstractions to user programs and managing the computer's resources. Mostly, the interaction between user programs and the

System Calls for Process Management
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System Calls for Process Management

The first group of calls in figure (a). deals with process management. Fork is a good place to start the discussion. Fork is the only way to create a new process in POSIX. It produces an exact duplicate of the

System Calls for File Management
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System Calls for File Management

Many system calls relate to the file system. In this section we will look at calls that operate on individual files; in the next one we will study those that involve directories or the file system as a whole.

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