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Super Telnet switch sever

Posted by Ktech | 04:40

displayed and then the second half frame is displayed shifted so that its lines fit between the lines of the first frame. This is...

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Beyond VGA – Super VGA

Posted by Ktech | 04:39

As VGA became the accepted new standard, boards manufacturers first concentrated on building compatible boards, then they turned t...

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Network hosting plane

Posted by Ktech | 04:37

screen can merge into the another smoothly and this gives the impression of a higher resolution. In additional to being able to ...

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Ram lesson Key points

Posted by Ktech | 10:08

Ø The disk controller interface governs the maximum data transfer rate. IDE, SCSI and ESDI are roughly twice as fast as the tradition...

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Ram working Keeping it fast

Posted by Ktech | 10:06

One phenomenon that many users of high performance computer notice is the gradual deterioration in the speed of access of their di...

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Sunday, 4 October 2015

displayed and then the second half frame is displayed shifted so that its lines fit between the lines of the first frame. This is called interlace and it succeeds in lowering the frame rate without increasing the flicker – it is used quit successfully, for example in broadcast TV pictures.

Unfortunately, as far as computer video goes its effects are very poor. Because of the way that computer graphics often use alternate lines, or patterns of lines to make intermediate shades or colourss, this use of interlace often produces a strong and very noticeable flashing. It is possible to arrange a demonstration of interlaced video so that it looks acceptable by avoiding tones or colourss that use regular odd/even line patterns. Equally, it is possible to find displays that make and interlaced Super VGA is tolerable as long as you avoid even grey tones. Some applications packages are even altering there colours scheme to avoid flicker on interlaced systems – Ventura 4 for instance gives the user the option of changing the grey surround to an even colours to reduce flicker.

Some Super VGA boards support non-interlaced monitors and even increased vertical scan rates up to 70Hz. Changing to a non-interlaced monitor makes the biggest difference but a scan rate of 70Hz is also worthwhile. Notice that to make use of non-interlaced high scan rate modes you need a video card and monitor that supports them.

Beyond VGA – Super VGA

As VGA became the accepted new standard, boards manufacturers first concentrated on building compatible boards, then they turned their attention to expanding on the capabilities of basic VGA. The highest resolution supported by a VGA board is 640x480 in 16 colourss from a palette of 256. This is adequate for general work but still higher resolution is required for applications such us DTP, CAD and illustration. Even general applications working under Windows or OS/2 benefit from resolutions above 640x480.

The need for these higher resolutions has resulted in the adoption of three additional standard modes.

Ø 800 x 600 in 16 or 256 colourss

Ø 640 x 480 in 256 colourss

Ø 1024 x 768 in 16 or 256 colourss

Network hosting plane

screen can merge into the another smoothly and this gives the impression of a higher resolution.

In additional to being able to display 256 colourss these can be selected form a palette of over 250,000 colourss. Compared to the prattle of 16 colourss made available by other adapters this is an incredible number and it makes it possible to produce very subtle colours changes.

If you find this discussion of video standard confusing then the following table provides a summary. That is important however is that VGA provides a standard that is backward compatible with all of the other video modes.

Resolution	Colourss	Palette	Adapter
320 x 200	2	16	CGA-EGA-VGA
320 x 200	16	16	EGA-VGA
320 x 200	256	256K	VGA
640 x 200	2	16	CGA-EGA-VGA
640 x 200	16	16/256K	EGA-VGA
640 x 200	4	64/256K	EGA-VGA
640 x 200	16	64/256K	EGA-VGA
640 x 200	2	256	VGA
640 x 200	16	256	VGA
720 x 348	2	2	HGA-EGA-VGA

Wednesday, 23 September 2015

Ram lesson Key points

Ø The disk controller interface governs the maximum data transfer rate. IDE, SCSI and ESDI are roughly twice as fast as the traditional ST-506 interface.

Ø The speed of a disk drive depends mainly on its access time. Drivers with access times of 25ms or less are generally considered fast.

Ø IDE drives are good choice for all single-user machines that need disks up to 500 Mbytes. Over 500 Mbytes, and for network file servers, the choice is between ESDI or SCSI.

Ø ESDI drives are simple and standardized. SCSI drives are more sophisticated and so potentially higher performing but they are less standard.

Ø Sector interleave is used to match the data transfer rate of the controller and processor to the maximum transfer rate of the disk. Too little sector interleave is far worse than too much.

Ø A catching disk controller provides the ultimate in disk performance and it is the natural partner for MCA or EISA bus machines.

Ø Software disk catching, or the use of a RAM disk, provides useful speed gains in disk access but uses main memory.

Disk fragmentation slows disk operations but can be avoided by using a defragmentation utility. Incipient disk errors can also cause a disk to slow down

Ram working Keeping it fast

One phenomenon that many users of high performance computer notice is the gradual deterioration in the speed of access of their disk drives over time. Many think that this is a psychological effect, other think that it is to do with the disk being too full. Neither of theses explanations is correct the slowing of disk systems with use it due to fragmentation. When you start using a hard disk there is generally plenty of unused space available in large contiguous chunks. This allow the operating systems to allocate storage to files, even large files, so that they are stored in one place of the disk. A file that is stored using sectors that are contiguous is fast to read and write.

However as the disk is used free space is used up (and also created) by the deletion of files. Slowly but surely the free space becomes broken up across the disk’s surface and eventually it isn’t possible for the operating systems to find chinks of free space large enough to store a file in one place. In this case the file will be stored using two or more chunks of free space – i.e the file is stored using non-contiguous sectors. This makes the file slower to read and write because the drive’s heads have to be moved across the surface of the disk to read the entire file . this is fragmentation and its effect can be a dramatic slow-down in the operation of a disk. You van often tell a badly fragmented disk by the sound or the head moving from track to track as a file that is scattered across the surface is retrieved. It gives the impression that the drive is working hard for simple file operations.

The solution to the problem is to reorganize the use of the disk so that fragmented files are stored using contiguous sectors and the free area of the disk is again composed of contiguous sectors. The reorganization of the existing files results in an immediate improvement in the read time and the newly contiguous area of free space means that fragmentation will not occur again when files are created. Thus defragmentation improves , both read and write times back to the original performance of the disk as first delivered. Of course , as the disk is used and files are created and deleted fragmentation will slowly develop but another session defragmentation soon cures that.