Do You Know ?

[Perfection]

Computer maintenance

Hard disks are vulnerable to heat, cold, magnetism, dust, fingerprint, liquids - tea, cool drinks & oils, software problems in programming etc. Ventillation (internal/external fans) & humidity controlled A/C will reduce the problems.

Touch ICs after discharging static electricity by touching the metal PC cabinet. Wrong connection (back ward), voltage fluctuation, lightning, electromagnetic interference etc. can damage ICs.

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Electrical safety

Voltage 20 to 30 and a current of 16 mA, 60 Hz are 'Let go' current. Voltage and current of higher value produce electric shock. 50 mA, 60 Hz : pain, fainting and exhaustion. Body (skin) resistance vary from person to person. Women are more sensitive to electric shock. Even 18 V AC can be fatal. Shocking effect of an ACV and 3 times DCV are equal.

Insulation of live wire are degraded by Ozone, UV light, nuclear radiation, heating, acids (HCl), vibration, mechanical damage, biological reasons (eaten by insects) etc.

Neils Bohr and his son got Nobel prize in Physics in 1922 and 1975.

[Perfection]

Fuzzy logic

Fuzzy logic products were first developed in Japan - fuzzy camcoders, washing machines, microwave ovens, carburetors and so on. It works on a logic condition grey neither black (0) nor white (1). We can't put black and white labels on things, it is relative. Similarly about true and false. A damaged car is again a car. So most statements are indeterminate, grey, fuzzy and probable.

Cretan's liar paradox : A liar from Crete said that all Cretans are liars and asked if he lied. He seemed to lie and not lie at the same time.

Are you satisfied with your job ? , answer will be grey.

Betrand Russel's barber : There is only one barber in the area. A notice at the barber shop reads "I shave all, and only, those men who do not shave themselves". So who shaves the barber ?.

If he shaves himself, then by his sign he does not. But if he does not shave himself, then by his sign he does. He seems both shave and not shave himself at the same time.

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Yin - Yang equation in fuzzy logic is A = not A or Half glass of water = Half empty glass or 0 = 1.

Fuzzy logic washing machines, air conditioners, vacuum cleaners, antis kid brakes etc save energy/fuel/money. In auto engine (control fuel injection and ignition), auto transmission (selects gear, based on load), elevator control, traffic control, microwave oven, rice cooker (regulates steam temperature as per volume), auto focus in camera, cancels handheld filtering (shivering) in video camcoders, Television (auto colour, brightness and volume control), stopping a vehicle at a predetermined position, auto trouble shooter etc.

Software can produce a fuzzy logic system in minutes and the human brain has to tune it for real situations. Scientists are in search of developing a neural system, which can take our brains out of the loop and give fuzzy systems their own brain. Fuzzy engineers turn expert talk into fuzzy rules. An adaptive fuzzy system acts as a human expert.

Expert system consists of knowledge base and the inference engine. This uses black and white logic (0 and 1).

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RAID : Redundant Array of Independent Disks. Hard disks (HD) usually have multiple disks (2 or 3) called platters. HD platters are made of glass or glass-ceramic. Platters are coated with magnetic substances. A thin film of iron oxide is located over the platter with the help of electroplating mechanism called sputtering. The thin film media is virtually uncrashable and looks like a mirror. HD runs at 7200 rpm, 20 times faster than floppy disks.Speeds can be 10,000 or 15,000 rpm. Data transfer in Seagate Cheetah 73 LP HD (15,000 rpm) is 51.15 Mb/s. 900 plus sectors per track. Sector capacity of 512 bytes. Track density in HD is 5000 per inch. Seagate HD is the leader in the number of hard disk sales.

Sony introduced the first 3.5" floppy disk in 1983. The 1.44 Mb (1440 kb) floppy disk has 80 cylinders and two heads. Each track has 18 sectors. Floppy controllers use IRQ 6 (Interrupt Request). Floppy drives use 4 pin female connector for power (Pin 1 : Yellow-12 V, Pin 2 : Black-ground, Pin 3 : Black-ground, Pin 4 : Red-5 V) and a 34 pin data cable. Floppy disks use FAT system. Metal detector can damage floppy disks.

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PCI (Peripheral Component Interconnect ) bus is 32/64 bit wide.The interface used to connect a hard disk to PC is called IDE (Integrated Drive Electronics). IDE connector has 40 pins and pin 1 is identified by a stripe on the cable. Position 20 is blocked in IDE connector to prevent improper plugging.

HD has 4 pin power connector similar to that of floppy drive. Most of the HD uses both 5 V (for electronic circuitry) and 1 V for the spindle motor and head actuator. HDs have one or more logic boards mounted on them. They control the drive's spindle and head actuator systems. HD has Mean Time Between Failures (MTBF) of 300,000 to one million. SMART (Self Monitoring Analysis and Reporting Technology) provide failure protection for HD.

Preparing a hard disk for storage : Low level formatting (physical formatting), partitioning and High level formatting (logical formatting). During low level formatting, tracks are divided into sectors, creating the inter sector and inter track gaps and recording the sector header and trailer information.

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FAT (File Allocation Table) : 12 or 16 bit, with a maximum volume size of 2 Gb. It can have 255 characters in file name in Windows 9x/200/NT4 plus.

FDISK command does partition on hard disk. FDISK can create or remove partitions. Partitioning may cause loss of data. Partition Magic software partitions the disk without loss of data. FAT 32 uses 32 bit to identify the clusters, thus can have a maximum volume size of 2048 Gb. Recommended number of partitions in a disk is 2.

After the partition, the operating system does a high level formatting of HD. Format command does high level formatting in a HD, while low level formatting and high level formatting in a floppy disk.

A motor can become a generator and vice versa. During recording on a HD, the head changes electrical impulses to magnetic fields, and while reading the head changes the magnetic field back into electrical impulses. Heads are electromagnets whose voltage can be switched in polarity very quickly.

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CD ROM : Read only write once disk holds 74 minute video (682 Mb). The disk has 120 mm diameter, 1.2 mm thickness and a 15 mm (dia) hole at the centre.Disk is of polycarbonate wafer with a data access speed in between floppy and hard disk. Optical reading/writing is done by LASER. Windows 98 comes in 75 floppies, if here is no CD ROM.

DVD : Digital Versatile Disk can read using DVD ROM drive (which can play CD ROM too and is called combo drive). A single layer DVD can store 4.7 Gb while a double layer DVD can store 8.5 Gb and is 11.5 times the capacity of a CD. A double layer DVD can store 4 hour video. Label will be at the centre near the hole.

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CD ROM

Mastering and imaging software makes a CD bootable. Dirt is the biggest enemy of CD drives. Scratches, dirt, finger prints and other contamination are the main causes of problems with CD. Clean the CD with a soft cloth, start from the centre and emanate towards the edge radially. CD drive reads CD ROM optically using LASER (Light Amplification by Stimulated
Emission of Radiation) of 780 nm wave length. While writing, the high powered Laser burn the dye coated over the gold reflective layer. Thus it is called burning a CD. When burned dye changes from reflective to non reflective state. CD RW can be rewritten at least 1000 times with packet writing software.

The top surface of the disc is more fragile as lacquer coating is of the order of 6 to 7 micrometre. So don't write on CDs using ball point pen, use felt tip pens. When the read lens of CD drive become dirty, it can give read errors. Lens cleaner CDs are useful.

Most DVDs are ATAPI (ATA packet interface) uses 40 pin dual ATA cable. Universal interfaces like USB or Firewire are more efficient. USB 2.0 is a high speed USB.

Restarting the computer is a magic cure for all.

[Perfection]

FDISK command

In hard disk, partitioning is done by FDISK and high level format is by Format command. FDISK makes it possible for various operating systems to co-exist on a single hard disk. The two types of partitions are primary (bootable) and extended (non bootable).

The four IDE ports are Primary master, Primary slave, Secondary master and Secondary slave.

Windows 95 & MSDOS supports FAT 16 which allows not more than 65, 536 files per drive and maximum volume size of 2.1 GB. So partitioning is required for a 10 GB disk into 5 drives.

With FAT 32, a 2 TB (1 TB=1000 GB) hard disk, is identified by a single dive letter. Windows 9x cannot read NTFS. Drive letter allocations are C : First primary, D : Second primary, E : First extended and F : Second extended.

Partition magic software can do conversion of file systems (FAT, FAT32 & NTFS) without loss of data. One can undelete the partition, create, resize, split, move and merge partitions. Partition magic is faster than FDISK.