Computer Wikipedia

Introduction

RAM is an acronym for “Random Access Memory”. As the name “Random Access” suggests it implies that you can at any given time access any memory cell directly. It is also known as the “temporary memory” i.e. it holds the data only for a limited period of time, meaning when the system is shut off then the memory is lost.

How RAM works?

RAM is filled with many microscopic capacitors. These capacitors either are charged or they don’t hold any charge. If a capacitor is charged then it is given the value -1 and if it doesn’t hold any charge then it is assigned the value - 0. Suppose we have capacitors lined up and we end up having a combination “0100001” which represents A, or if we have combination “01100010” which say represents “B”.

This way every different combination can represent different characters. So we can have a bank of distinct capacitors to represent any transaction or application of the PC.

Each 1 or 0 is called a “Bit” and eight “Bits” together form a “Byte”. One million “Bytes” forms One Megabyte. Thus when we use the term like RAM storage of this computer is 512 MB it means that your RAM can represent 512 * Million characters. So the RAM storage on the computer is directly proportional to number of applications you can run your system.

Types of RAM

RAM stores the data either in the form of Flip-Flop as in SRAM (Static-RAM) or as a charge in the capacitor like in DRAM (Dynamic RAM), EPROM (erasable programmable read only memory), Flash memory, EEPROM (electrically erasable programmable read-only memory)

Another type is ROM (read only memory) that has permanently enabled/disabled transistors by using a metal task.

Traditionally SRAM and DRAM were used in most of the computers, but nowadays most of the products coming in the market such as music players and palmtop computers. use FLASH memory because it is non-volatile and the data can be electrically erased and reprogrammed. FLASH memory is further divided into NAND and NOR memory.

NOR type truly conducts the random access and is widely used as ROM. NAND does not support random access but is used for bulk storage like USB hard-drives.

Sometimes when your system runs out of RAM then it performs a certain function called “Swapping”. What happens during swapping is that area of your hard-drive is used as additional memory, but excessive use of Swapping may cause problems for your system because hard-disk memory is much slower than RAM. So, this excessive use of area of main memory as RAM can cause “Thrashing” which my cause your system to crash.

You can also partition portion of RAM, this allows RAM to act at a much faster rate and as a separate hard-disk.

Introduction

Pen Drive also referred as USB flash drive is a portable device which allows user to transfer data (text, images, videos etc) to and from computer quickly. Users can easily read and write the data on the Pen Drive by plugging it into the USB port on the computer. Pen Drives are quite compact and can fit easily into the pocket; they run without battery and draw power from the USB connection itself. Both Floppy disks and CDs are now being gradually replaced by Pen Drive as a preferred means of data storage. Its because latter offers mass data transfer and storage capability and at a much faster rate.

Storage capacity of the Pen Drive can vary from few megabytes to over 100 GB. Nowadays even external hard drives are available in the market with huge storage capacity, which like Pen Drive can be connected to a USB port on the computer.

Architecture

Pen drive consist of an electronic circuit board and a USB connector connects the drive to the computer. Pen Drive also known as a Flash memory is an example of NAND style storage device. It is a memory chip which holds the data. Data output is controlled by Crystal oscillator which produces 12 MHz clock signal in the device.

Most Pen Drives are covered with plastic, metal or rubber casing for insulation.

Advantages

Pen Drives are robust and scratch free thus ensuring maximum security for your data as compared to other traditional means of data storage. Many available PC software suites permit the launch of an operating system from the bootable pen drive. Moreover companies selling Pen Drives nowadays also couple it with other devices like MP3 music player, LED’s or Swiss Knife etc.

Hard disk drive or HDD is the basic component of any computer. Hard disk is in fact the data bank where all the information, programs and files are stored. Hard disk contains a round rotating metal disk called platter which is like a mirror in appearance and stores the data with magnetic recording medium. This magnetic recording medium stores the data via read/write head on the platters. These platters are quite delicate and should not be tampered with because even small damage can result in complete loss of data.

Unlike RAM (Random Access Memory) hard disk is classified as non-volatile storage memory as it does not requite continuous power supply to store the data.

Read and write heads are attached to the end of the platter and as mentioned are responsible for reading and writing the data on the hard disk.

These read and write heads are attached to the arm called actuator which moves over the platter of the hard-disk. The read and write head never actually touches the platter but just brushes past it with constant air cushion between both of them.

Platter rotates with the speed of over 5000 RPM in the hard disk. A component called spindle is actually responsible for rotating the hard-disk with such speed. The higher the RPM (rotations per minute) faster the data can be read/written on the hard-disk and thus it gives a much better performance.

Hard disk drives available in market come with varying storage capabilities ranging from few megabytes to hundreds of gigabytes. Previously computers used to have a hard drive with just few MB but nowadays most of the computers have over 50 GB of hard-disk space.

All the components mentioned like actuator, spindle platter etc. are contained in the unit called hard disk assembly (HDA). Logic board which controls the movements of these components is located outside HDA and facilitates the inward/outward movement of data.

Compact Disk or CD as it is commonly known is an optical disk used to store data and information. Made of a polycarbonate material and as light as 20 grams, CD has a standard radius of 6 centimeters. Philips and Sony were one of the first manufacturers of the CD in mid 1970’s, by the end of 1980’s CD were becoming highly popular and became as preferred means of data storage.

Any form of data be it music files, text files, graphics, movies etc can be stored on the compact disk. A standard CD has about 700-800 MB (megabytes) of data storage capacity. The data in CD is stored in the divisions called pits which are embedded in the spiral tracks over the polycarbonate layer.

This polycarbonate layer is in turn covered by reflective layer (usually aluminum) and on top of that is added another layer of acrylic is added for protection. Labels at last are etched on the acrylic layer.

CD-ROM player is a device which is used to read and write the CDs. The two types of CDs are CD-R and CD-RW. CD-R is a cheaper because the data once written on this can not be erased and stays there. Whereas CD-RW (read/write) is a re-recordable CD where you can re-write the data on the CD as an when you require. CD-RW is tad expensive than CD-R.

CD is a sensitive device which is quite vulnerable to dust and scratches. During recent years use of CD has dropped considerably because people prefer to the pen drives or the USB which much more portable and can hold large amount of data.