Different Types of RAM

!±8± Different Types of RAM

RAM is the acronym for 'random access memory' and is usually calculated in megabytes. A RAM chip is a module that holds freshly accessed information so that the central processing unit can have access to it. It is faster than reading from the hard drive and allows for easy access of recently stored data, information, and files. This means that all programs must be run through the RAM before they are usable.

There are two basic types of RAM, namely dynamic RAM and static RAM. A dynamic RAM is called so because it has to be constantly refreshed by the memory controller. The reason for refreshing is that the capacitors that hold the information or data have a built-in leak that can only be stopped by refreshing the information thousands of times in a second. This makes dynamic RAM slower and cumbersome compared to static RAM.

Static RAM is a type of random access memory that has a greater capacity for storage because it uses on-off switches instead of capacitors. However, static RAM is more expensive compared to dynamic RAM because it is faster and can hold more information.

Usually, advanced versions of the dynamic RAM are used instead of using static RAM because of its high price. These versions include FPM (fast page mode), ECC (error correcting code), EDO (extended data output), and SDRAM (synchronous dynamic RAM). ECC RAM is a special error-correcting RAM that is usually used in servers.

EDO RAM, or extended data output RAM, is an improvement of the traditional FPM RAM. Data can be read faster and the length of time that the output data is valid is extended, which improves time coordination between the central processing unit and RAM, thus improving the performance.

The speed of a RAM is measured in nanoseconds, and the fewer the nanoseconds (ns), the faster the computer. Today we use 50 ns computers as opposed to the 180 and 150 ns that we used in the last decade.

Different Types of RAM

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Facts About Single-Rotor RC Helicopters

!±8± Facts About Single-Rotor RC Helicopters

A single-rotor R/C helicopter consists of a main and tail rotor. The 2 rotors work together to control the stability and maneuverability of the helicopter. Many pilots who are proficient in flying a dual-rotor or coaxial rotor R/C helicopters find single-rotor models a little different. Beginners are not recommended to start with a single-rotor model because of its complexities. The pilot must have a complete understanding of important aspects such as applying throttle to the main rotor, maneuvering of the tail rotor, setting variable pitch to the blades and many more.

A flight simulator is highly suggested before diving into your first single-rotor helicopter adventure. It will give you the feel of an actual single-rotor experience without the hassles and troubles of crashing. That will definitely save you some money and time! Other training apparatus and crash kits can also aid you during your first few flights. A training gear is a set of equipment and supplies that is hitched up onto the landing skid to avoid severe damage. These are similar to carbon rods with orange ping pong balls mounted on ends. Crash kits are basically spare parts readily available in case of a crash or any other smash up.

Major parts and components: An R/C helicopter with a single-rotor generally has either a belt-driven or motor-driven rotor tail. A belt drive gives superior control though an electric motor is less expensive. The tail rotor has the responsibility of preventing the body from rotating against the directions of the main rotor blades. Basic models of single-rotor R/C helicopters have main rotor blades that do not change angle. This is referred to as Fixed Pitch (FP). On the on other hand, advanced types have the Collective Pitch (CP). Helicopters with FP cost much lower but slower than CP helis.

Cheap ready-to-fly (RTF) single-rotor helicopters come with 'brushed motors'. More sophisticated types have 'brushless motors'. This type requires a specific electronic speed controller (ESC) that increases the power and flight time significantly. Rotor heads and tail assemblies are usually made of either plastic computer numerical controlled (CNC) machined aluminum. Most professional aerobatic pilots prefer the CNC type because it results to smoother and more predictable flights if configured properly. It also enhances the helicopter's appearance even if it adds to some weight and cost. Other electronic components that may vary are the following: gyros, radios, servos, and speed controllers.

There is a website that has great information on RC Helicopters, the website is called: RC Helicopters World, and can be found at this url:
http://www.rc-helicopters-world.com

By Robert W. Benjamin

You may publish this article in your ezine, newsletter, or on your web site as long as it is reprinted in its entirety and without modification except for formatting needs or grammar corrections.

Facts About Single-Rotor RC Helicopters

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Do You Pronate Or Over-Pronate? That is the Question

!±8± Do You Pronate Or Over-Pronate? That is the Question

I've Been Told my Feet Pronate, What Does Pronate Mean?

If you pronate it means you turn or rotate your foot inward when weight is applied. The heel bone angles and the arch tends to collapse, often causing a 'knock-kneed' position. To pronate is a normal motion of the foot that allows the foot to absorb shock as it hits the ground. However, when you pronate too much, the complete force of your weight is not properly distributed. When the arch collapses too much, it reaches its end point and no longer works to absorb impact.

Overpronation also places the joints, ligaments, tendons, muscles, and other soft tissues around the foot and ankle in a compromised position. This creates a mechanical problem with your walking cycle and alters alignment at the feet, knees, hips, and back. It can cause pain and problems in any of these areas.

What Harm Can Overpronation Do?

If you pronate too much while walking or standing, you are at risk for developing several conditions. These may include: foot pain, knee pain, shin splints, Achilles tendonitis, plantar fasciitis, heel spurs, back pain, and many others. People who pronate too much are often said to have flat feet and often experience overuse injuries such as stress fractures and tendonitis.

How Do I Know If I Pronate Too Much?

One sign that shows you may over-pronate is your shoe wear. Take a look at the inside of the shoe to see if there is more wear here than on the outside.

If you pronate too much your heel bone will appear angled with the inside of your ankle moving in over the inside of the heel. If you view your feet from the side, you can check to see if there is space between the arch and the floor or if the arch lays flat when you are standing. If it does lay flat, you have flattened arches and probably pronate too much. You will also see this with a wet footprint...your print should show a space for the arch. If it doesn't you probably over-pronate.

What Can I Do To Help If I Over-Pronate?

Often your doctor will prescribe orthotic insoles to help with your condition. Orthotic insoles work to correct abnormal foot motion and alignment. They are designed to prevent you from pronating too much. Foot orthotics designed for overpronation have a good arch support and usually tip your foot away from the pronated position. They are also firm enough that they do not collapse under your weight when you stand on them.

One of the most important decisions you can make is which footwear you choose. When choosing a shoe, make sure you choose one with very good support and a strong heel counter. This will help control the motion of your feet and help any orthotic insoles you may be using to do their job better.

Foot muscle strengthening exercises may also be helpful. A physiotherapist or physical therapist would be the best person to help you with these exercises.

If you pronate, but are not experiencing any symptoms, you may want to use over the counter orthotic insoles to control your pronation. Most over the counter foot orthotics are too soft to control movement and will allow pronation to occur, but there are some that are firm enough to help stop you from pronating. They may be very beneficial in preventing future problems caused by overpronation.

Do You Pronate Or Over-Pronate? That is the Question

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How to Create and Manage Access - Control Lists on Cisco ASA and PIX Firewalls

!±8± How to Create and Manage Access - Control Lists on Cisco ASA and PIX Firewalls

Access Control Lists (ACLs) are sequential lists of permit and deny conditions applied to traffic flows on a device interface. ACLs are based on various criteria including protocol type source IP address, destination IP address, source port number, and/or destination port number.

ACLs can be used to filter traffic for various purposes including security, monitoring, route selection, and network address translation. ACLs are comprised of one or more Access Control Entries (ACEs). Each ACE is an individual line within an ACL.

ACLs on a Cisco ASA Security Appliance (or a PIX firewall running software version 7.x or later) are similar to those on a Cisco router, but not identical. Firewalls use real subnet masks instead of the inverted mask used on a router. ACLs on a firewall are always named instead of numbered and are assumed to be an extended list.

The syntax of an ACE is relatively straight-forward:

Ciscoasa(config)#access-list name [line number] [extended] permit protocol
source_IP_address source_netmask [operator source_port] destination_IP_address
destination_netmask [operator destination_port] [log [[disable | default] | [level]] [interval seconds]] [time-range name] [inactive]

Here's an example:

asa(config)# access-list demo1 permit tcp 10.1.0.0 255.255.255.0 any eq www
asa(config)# access-list demo1 permit tcp 10.1.0.0 255.255.255.0 any eq 443
asa(config)# show access-list demo1
access-list demo1; 2 elements
access-list demo1 line 1 extended permit tcp 10.1.0.0 255.255.255.0 any eq www
access-list demo1 line 2 extended permit tcp 10.1.0.0 255.255.255.0 any eq https

In the above example, an ACL called "demo1" is created in which the first ACE permits TCP traffic originating on the 10.1.0.0 subnet to go to any destination IP address with the destination port of 80 (www). In the second ACE, the same traffic flow is permitted for destination port 443. Notice in the output of the show access-list that line numbers are displayed and the extended parameter is also included, even though neither was included in the configuration statements.

You can deactivate an ACE without deleting it by appending the inactive option to the end of the line.

As with Cisco routers, there is an implicit "deny any" at the end of every ACL. Any traffic that is not explicitly permitted is implicitly denied.

**Editing ACLs and ACEs**

New ACEs are appended to the end of the ACL. If you want, however, to insert the new ACE at a particular location within the ACL, you can add the line number parameter to the ACE:

asa04(config)# access-list demo1 line 1 deny tcp host 10.1.0.2 any eq www
asa04(config)# show access-list demo1
access-list demo1; 3 elements
access-list demo1 line 1 extended deny tcp host 10.1.0.2 any eq www
access-list demo1 line 2 extended permit tcp 10.1.0.0 255.255.255.0 any eq www
access-list demo1 line 3 extended permit tcp 10.1.0.0 255.255.255.0 any eq https

Notice in the first line of the example above that an ACE is added at line one in the ACL. Notice in the output from the show access-list demo1 command that the new entry is added in the first position in the ACL and the former first entry becomes line number two.

You can remove an ACE from an ACL by preceding the ACE configuration statement with the modifier no, as in the following example:

Asa04(config)#no access-list demo1 deny tcp host 10.10.2 any eq www

In my next article, I'll show you how to use time-ranges to apply access-control lists only at certain times and/or on certain days. I'll also show you how to use object-groups with access-control lists to simplify ACL management by grouping similar components such as IP addresses or protocols together.

Copyright (c) 2008 Don R. Crawley

How to Create and Manage Access - Control Lists on Cisco ASA and PIX Firewalls

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