tech-crush

In my first post I would like to differentiate between a hacker and a cracker, since these two terms are used interchangeably but don’t mean the same.

A Hacker is a person who breaks into(not necessarily manually) another computer system, or any network or rather say into his own for some good purpose, i.e., with good intentions wehereas a Cracker is a person who breaks into another computer system or any network for some unlwfull, illegal purpose or with some bad intentions.

There are basically two cache write policy:-

1. Write throuogh:- In this case, whatsoever changes have been made in the cache are immediately reflected in the memory.

2. Write back:- In this case, whatsoever changes are made in the cache, are made at the end, i.e., just before the content in the cache is to be replaced with new content, or being deleted. Thus it should also be clear by now why a miss in write back cache will take more time than write through since in write back before bringing the required data the old data needs to be updated in the memory i.e the write through cache mechanism requires more clock cycle.

In write back policy, whichsoever data needs to be updated, is marked, also called dirty bit.

First the cache is searched, and if the data is found there, then data is retreived from there, this is termed as cache hit, if the data is not found there then it is termed as cache miss.If  a cache miss occurs then most of the time the cache will replace it’s entry.If a miss occurs then the data retreival takes time cause it has to be retreived from the memory or auxillary memory, both of which are slower than the cache.

This type of memory is made up of SRAM cells as discussed previously. These are faster than RAM. The processor first searches the cache then the RAM, if the required instruction is not present in both of them then it’s retrieved from the auxiliary memory. The instruction stored in cache and RAM is according to the principle of locality of references. Nowadays the processor comes integrated with the cache. Only few years ago the processors manufacturer’s used to mention the size of the cache in KB’s(Kilobytes), now the latest processors mention it in MB’s(Mega Bytes), hence pushing the performance limit.

DDR stands for Double data rate RAM’s, one of the latest technologies in RAM. DDR2 is the 2^nd generation of technology in it. DDR2 is faster and better than DDR. DDR2 are at present ruling the market. DDR3 is also out but because of their price they are not in such demand as DDR2.

DDR3 is being used in graphics card for high performance. Most of the companies manufacturing RAM’s do give lifetime warranty. For e.g., Transcend, Kingston, etc. Don’t compromise with the quality of your RAM, since that may lead to inefficient performance of the system as well as may cause damage to other branded parts too. There are lot many substandard RAM’s available in the market today at very attractive prices. Make sure you take only reliable ones like Kingston.

Basically memory is of two types.

1. Static

2. Dynamic

The Static type is better in technology than dynamic.

DYNAMIC MEMORY

In dynamic type memory the information is stored in form of charge inside the capacitor. Since practical capacitors have the property of losing charge they need continuous refreshing circuit, hence as long as power is supplied to it, it can retain the data. As soon as the power supply is removed the data will be lost cause of the discharging action of the capacitor.

The Dynamic type memory(DRAM) technology is simpler and cheaper than static type memory. The DRAM’s(stands for dynamic random access memory) are dense too. These basically use a capacitor and a transistor to store a bit as charge.

This is shown in the diagram below.

Since this loses the data this is also known as volatile memory. The transistor allows the charge to flow inside the capacitor according to it’s biasing(i.e. forward or reverse biasing). The biasing determines whether the capacitor will get charged or discharged. Say the transistor is in the forward biasing condition, then the collector follows the emitter(i.e. the emitter current is almost equivalent to collectors current), then the capacitor will get charged. Then for storing this charge we can put the transistor in cutoff region(both region are reverse biased). Then for discharging of the capacitor(say for storing of a new value) we can have the transistor in the reverse active mode. In this mode the collector and emitter will switch there roles and lead to capacitor discharge.

STATIC RAM

This kind of RAM does not need any kind of refreshing circuit. These are faster than DRAM’s , these are usually employed along with DRAM in a system to get an average good speed at an economical price.

These employ transistors to store the data. They don’t consist of any capacitor hence do not need any refreshing circuit.

The cache is SRAM memory. This has faster access time than DRAM memory. The DRAM has fewer components hence can have more memory per unit area even though it’s access time is slower. In this kind of memory the data is stored by the state of the conduction which means that either the right or left side of the transistor is conducting.

Both the DRAM and SRAM lose the information when the power supply is removed.

The following figure shows the SRAM cell.

This can be basically divided into two categories.

1. ATX form factor-This stands for Advanced Technology Extended.

2. BTX form factor- Balanced Technology eXtended Form Factor.

The latter is better since this overcomes the shortcomings of ATX. The motherboards are designed according to the form factor technology. BTX is the latest one. One of the changes in this is that the memory slots have exchanged positions with the expansion slots. This change will facilitate the flow of air to be shared by many system components for e.g. processor, chip[set, etc.

BTX allows easy integration of component’s in the system that are interpolable.

This is usually a metal and plastic case. This contains the basic parts of the computer like motherboard, graphics card, etc. PCs have been packaged in a number of different case designs. These designs fall into three basic styles:

· Desktops

· Towers

· Portables

Each design has it’s own advantages. The design choice depends upon the user’s choice and space.

How stuffs are organized inside does vary in these designs.

Desktops

These designs are designed to sit horizontally on a desk top(and hence the name). The original IBM-PC,XT and AT use this case styles.

A narrower desktop style, referred to as a baby AT case, was developed to take up less desk space than XT and AT. The reason behind it being a half-height power supply unit. This limits the number of disk drives.

System indicator lights and control buttons are built into the front panel. . The common ones being the system power light, and HDD activity light (i.e. when it’s blinking it’s being accessed otherwise not). The system indicator lights may also include a turbo speed indicator light.

Control buttons are also build in the front of the system case. These may be used for restarting the system, a power switch and a turbo speed selection switch.

The cover of the system unit slides off the base. The top of some designs slides forward after screws securing it to the back panel have been removed. The fit between the top and the case is very important in achieving FCC certification. A tight fit and electrical conductivity between the case and top are necessary to prevent unwanted radio interference from escaping the interior of the case.

A fan in the power supply unit pulls in air through gaps in the front side of the case, which flows over the components inside. Special IC coolers are added over the microprocessors to keep them cool. They are designed to be fitted directly onto the IC and plug into one of the power supply’s connectors.

Towers

Such cases are designed to sit vertically. These are the most common these days. Mini towers and Mid towers are short towers are designed to take up less vertical space.

Selection of Cabinet’s for Pc’s

The most important thing to consider that you should keep in mind while purchasing a cabinate for an assembled Pc is the ventilation. Make sure it has lot many holes so that hot does not accumulate inside the cabinet. Additional fans are good for ventilation purposes. Two fans one for inlet of fresh air and one for outlet of hot air is a good idea.