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THIN CLIENTS
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THIN CLIENTS

For many years, the main computing model has oscillated between centralized and decentralized computing. The first computers, such as the ENIAC, were, in fact, personal computers, albeit large ones, because only one person could use one at once. Then came timesharing

Graphical User Interfaces
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Graphical User Interfaces

The majority of personal computers offer a GUI (Graphical User Interface). The short form GUI is pronounced "gooey." The GUI was invented by Douglas Engelbart and his research group at the Stanford Research Institute. It was then copied by researchers at Xerox PARC. One fine day,

Output Software
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Output Software

Now let us look at output software. First we will examine simple output to a text window, which is what programmers usually prefer to use. Then we will look at graphical user interfaces, which other users often prefer. Text Windows Output is simpler than input when the output is sequentially in a single font, size, and color. For the most part, the program sends characters

USER INTERFACES: KEYBOARD, MOUSE, MONITOR
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USER INTERFACES: KEYBOARD, MOUSE, MONITOR

Every general-purpose computer has a keyboard and monitor (and usually a mouse) to allow people to interact with it. Although the keyboard and monitor are technically separate devices, they work closely together. On mainframes, there are frequently many remote users, each with

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

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:

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

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

Error Handling
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Error Handling

Disk manufacturers are constantly pushing the limits of the technology by increasing linear bit densities. A track midway out on a 5.25-inch disk has a circumference of about 300 mm. If the track holds 300 sectors of 512 bytes, the linear recording density may be about 5000

Disk Arm Scheduling Algorithms
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Disk Arm Scheduling Algorithms

Now we will consider some issues related to disk drivers in general. First, look at how long it takes to read or write a disk block. The time needed is determined by three factors:For most disks, the seek time dominates the other two times, so reducing the mean seek time can improve system performance considerably.