Minicomputer

                              What is Minicomputer?  

A minicomputer isn't very mini. At least, not in the way most of us think of mini. You know how big your personal computer is and its related family. A workstation is the next step up in size, performance, and price, and is similar to a personal computer in that it is used by one individual.

Then comes the minicomputer. A minicomputer costs from $20,000 to $200,000 or so. It is built to perform different tasks for different people at the same time. Each person using a minicomputer has their own terminal attached by wires or via a modem to the computer proper. (A terminal isn't a computer-it's basically just a keyboard and a monitor; see the full definition.) The minicomputer spends a little bit of time on one person's task, then moves on to the next, and so on, juggling the work based on which jobs it thinks are most important. If you're the only one using a minicomputer, this can be one fast machine.

But once many users (people) are "on" the system, the thing begins to slow down-you may type something and then wait for a minute or more before you see a response on the screen. Minicomputers used to be the only option for companies. Now, many firms are turning to networks of personal computers to accomplish the same thing faster and cheaper.


Chapter : Introduction to Computer

• Computer Fundamental 

 

Access time

                               What is access time? 

  Access time refers to how fast the disk or memory can locate and begin retrieving (accessing) a specific piece of information or transfer data to the CPU. A low access time indicates a fast hard drive. Access time is measured in milliseconds, or ms. when making comparisons, look for 'memory access time' (measured in nanoseconds), Memory access time refers to the time it takes to transfer a character from memory to or from the processor, and/or 'disk access time' (measured in milliseconds) refers to the time it takes to place the read / write heads over the requested data. Sometimes the speed of a disk drive is measured by the rate at which it transfers data - in this case, a higher' data transfer rate' indicates a faster drive. For a disk drive the access time includes both the head SEEK TIME and the LATENCY.

For a disk, total access time is the sum of seek and rotational times to reach a particular record. RAM may have an access time of 80 nanoseconds or less, while hard disk access time could be 18 milliseconds or less.

For a floppy drive, the average access time is 25 ms; the access times for CD-ROMs approximately twice as long as for floppy disks.

For a drum or fixed-head disk, average access time is a half-revolution and maximum access time is a full revolution, since both have heads that are fixed over the data areas. Average access times for drums are 5 to 10 ms.


Chapter : Introduction to Computer

• Computer Fundamental 

Coprocessor

                                      What is coprocessor?  

A coprocessor is a chip that works side-by-side with the computer's main processor (the chip called the central processing unit, or CPU). The coprocessor handles some of the more specialized tasks, such as doing math calculations or displaying graphics on the screen, thereby taking some of the work load off the main processor so it can go on with the business of directing and keeping order over the whole show. A coprocessor is installed to reduce the burden on a computer's CPU and thus free it for more general duties such as transferring data and handling multiple tasks. 

Math coprocessors, for example, are specialized for performing calculations on numbers, and they are much faster at it than the main processor in your computer. So if you have a program that does many math calculations, such as a spreadsheet or a CAD program, then adding a math coprocessor to your system can sometimes remarkably improve your computing speed.

There are video coprocessors that are used to speed up the display of graphics on your screen. Again, if you use any graphics-based application, including Windows, then adding a video coprocessor to your system on an add-in board can speed up your system even more than buying a faster computer.

One catch, however, with any kind of coprocessor, is that the software you use must be written so that it knows the coprocessor is there, otherwise your system will not recognize its existence and won't be able to use it.

A coprocessor may be designed to work just with a particular type of CPU, in which case its instructions can be included in the main program and are passed on to the coprocessor by the CPU as it encounters them. In other cases, the coprocessor may require its own separate program and program memory, and communicates with the CPU by interrupts or message passing via a shared memory region.




Chapter : Introduction to Computer

• Computer Fundamental 

32-bit addressing

                         What is 32-bit addressing?  

If a computer uses 32-bit addressing, that means the address can have 32 numbers. With the possibility of each number being either a one or a zero, there are 4 billion different addresses available (232). Four billion bytes (each memory location holds one byte) is 4,096 megabytes, which is 4 gigabytes. So with 32-bit addressing you can theoretically address 4 gigabytes of memory.

Alas, at this point in technology there are still some limitations in the hardware, so you can't really install and use (address) all 4 gigabytes. A PC with an 80386 or 80486 microprocessor can address 4 gigabytes of memory all right, but they don't make PCs that can hold that many memory chips. The most a modular Mac (any of the Mac II family) can address is "only" 128 megabytes, and some of the Quadra’s can go up to 256 megabytes.

 

 

Chapter : Introduction to Computer

• Computer Fundamental 

AUTOEXEC.BAT File

                       What is AUTOEXEC.BAT File?  

The name of this batch file comes from a combination of the words automatically executed batch file. Like other batch files, AUTOEXEC.BAT contains a series of DOS commands that your (IBM-compatible) PC runs for you, one after the other, so that you don't have to type the commands individually. It gives the computer various basic instructions about starting Windows, running antivirus checks in the background, identifying the keyboard, and so on.

The file was typically used to issue configuration and initialization commands to the operating system and PERIPHERAL devices such as CD-ROM drives and sound cards, a typical entry being. What's special about AUTOEXEC.BAT is just that DOS automatically runs this particular batch file each time you turn on or restart the computer. Most people wind up calling AUTOEXEC.BAT the "AUTOEXEC" file for short.

AUTOEXEC.BAT must be stored in the ROOT DIRECTORY of the computer's BOOT DRIVE in order to be found and executed, and the commands it contains follow the same syntax as any other MS-DOS BATCH File, that is, a list of operating system commands exactly as they would be typed manually at the COMMAND PROMPT, plus certain control structures such as GOTO that cannot be deployed manually.

You can customize the AUTOEXEC file yourself, filling it with exactly the commands you want to get your system up and running to your specifications and to suit the needs of your software and peripherals. AUTOEXEC.BAT is typically used to set the look of the DOS prompt, tell DOS which directories it should search when looking for programs to run, configure the serial ports, load the mouse driver, and start memory resident programs and utilities. If you like, you can use the AUTOEXEC file to start a particular application program (such as your word processor) or to start Windows.

Here's an excerpt from a typical AUTOEXEC.BAT file:

PROMPT $p$g

PATH=C: \ WINDOWS;C: \DOS;C: \ UTILS

SET TEMP=D: \ TEMP

These lines set the DOS prompt to show the current directory; set the DOS path; and tell the system to look for temporary files in the D: \ TEMP directory.

BOOT

The process of starting or restarting a computer. Boot is a process that the computer goes through to get ready to receive input. During this boot process, certain configuration files, such as the AUTOEXEC.BAT, are used. For example, at startup, the commands in AUTOEXEC.BAT are executed one at a time automatically, without the user typing them in.

BATCH FILE

A type of executable file that contains a "batch" or listing of DOS commands to be executed in order, as if the user had typed each one in separately. One example of a batch file is the AUTOEXEC.BAT, whose instructions are executed whenever the system is booted.

DOS PROMPT

A symbol that indicates DOS is ready for the next command. The DOS prompt generally looks like C:\>, but it can be changed by commands in AUTO.EXEC.BAT.





Chapter : Introduction to Computer

• Computer Fundamental 

 

Mainframe computer

                       What is mainframe computer?  

The term mainframe has shifted from its original reference to the main housing, or frame, that contained the central processing unit (CPU) of the computer. In those days, all computers were big-like the size of a garage-and the frame for the CPU might have been as big as a walk-in closet. Now mainframe refers to the kind of large computer that runs an entire corporation.

While "large" can still mean as big as a room, most of today's mainframes are much smaller, although they're still quite a bit bigger than a personal computer or even a minicomputer. A mainframe has an enormous storage space on disk and tape (like thousands of kilobytes, measured in gigabytes), and an enormous amount of main memory. Theoretically, it works a lot faster than the fastest personal computer. A mainframe also costs big bucks, from half a million or so on up.

Mainframes are tended by special technicians who feed them the programs they run and who scramble around trying to fix them whenever they stop working, which is often. All mainframes are multi-tasking, multi-user machines, meaning they are designed so many different people can work on many different problems, all at the same time.

Mainframes serve most often as information stores and processors. An army of smaller computers is connected to the mainframe. These smaller computers are not in the same room; they may be connected through phone lines across the world. Ordinary people in the company never touch the mainframe itself. Instead, they interact with the computer using a terminal, which is more or less a keyboard and a monitor connected to the mainframe with wires, or by modem over the phone lines. People use the smaller computers and get information from and send information to the mainframe.

The difference between a minicomputer and a mainframe is arbitrary, and different people may use either term for the same machine. Even if you don't work for a large company, you might have contact with a mainframe: when you connect to an online information service or a commercial e-mail service from your personal computer, you are often connecting to a mainframe.

In the '60s the mainframe vendors were called "IBM and the seven dwarfs": Burroughs, Univac, NCR, Control Data, Honeywell, GE, and RCA. They turned into IBM and the BUNCH after Honeywell ate GE's computer division and Univac ate RCA's.




Chapter : Introduction to Computer

• Computer Fundamental 

 

Bus Contention

                               What is Bus Contention?  

Bus Contention: A loss of performance that can arise when two or more devices – for example computer PROCESSORS or disk controllers - try to transfer data simultaneously over the same BUS. For example hesitation may be introduced into a video or audio playback whenever the disk is being accessed. Contention is ameliorated by some kind of ARBITRATION scheme that regulates bus usage in a fair and orderly way, ensuring that all the contending devices are granted access for a reasonable duration and within a reasonable time ..It can be avoided altogether by changing the hardware architecture so as to provide separate buses for each device. 




Chapter : Introduction to Computer

• Computer Fundamental