Memory access i s When memory is read or written  , a specific procedure is used to control each access to memory, which consists of having the memory controller generate the correct signals to specify which memory location needs to be accessed, and then having the data show up on the data bus to be read by the processor or whatever other device requested it.

Memory controller is the part of the system that controls the memory byt generating the necessary signals to control the reading and writing of information from and to the memory, and interfaces the memory with the other major parts of the system. It can be a separate chip or integrated into another chip, such as on the  microprocessor.

Memory controllers contain the logic necessary to read and write dynamic random access memory (DRAM), and to “refresh” the DRAM by sending current through the entire device. Without constant refreshes, DRAM will lose the data written to it as the capacitors leak their charge within a fraction of a second.

DRAM VS RAM :

DRAM is dynamic in that, unlike static RAM , it needs to have its storage cells refreshed or given a new electronic charge every few milliseconds.  RAM does not need refreshing because it operates on the principle of moving current that is switched in one of two directions rather than a storage cell that holds a charge in place.  RAM is generally used for cache memory, which can be accessed more quickly than DRAM.

Only one transistor and a capacitor are required per bit, compared to four transistors in RAM. This allows DRAM to reach very high density. Unlike flash memory, it is volatile memory , since it loses its data when the power is off.

in brief :

Advantages: it’s compatible with just about everything. Disadvantates: it’s the slowest of the memory types currently available and because it isn’t in demand

‘Ferrites’ are a class of chemical compounds with the formula AB2O4, where A and B represent various metal cations, usually including iron. These ceramic materials are used in applications ranging from magnetic components in microelectronics.

You normally see these “bumps” on the mouse, keyboard and monitor cables. You can also find them on power supply wires when a device (like a printer or scanner) uses an external transformer.

These “bumps” are called ferrite beads or sometimes ferrite chokes put to reduce EMI (electromagnetic interference) and RFI (radio-frequency interference).

It is a passive electric component used to suppress high frequency noise in electronic circuits. Ferrite beads employ the mechanism of high dissipation of high frequency currents in a ferrite to build high frequency noise suppression devices. Ferrite beads may also be called ferrite cores, ferrite rings, ferrite EMI filters.

These cables act as nice, long antennae for the signals they carry. They broadcast the signals quite efficiently. The signals they broadcast can interfere with radios and TVs. The cables can also receive signals and transmit them into the case, where they cause problems.

A keyboard’s primary function is to act as an input device. Using a keyboard, a person can type a document, use keystroke shortcuts, access menus, play games and perform a variety of other tasks.

A keyboard typically has characters engraved or printed on the keys and each press of a key typically corresponds to a single written symbol. However, to produce some symbols requires pressing and holding several keys simultaneously or in sequence. While most keyboard keys produce letters, numbers or signs (characters), other keys or simultaneous key presses can produce actions or computer commands.

keyboards have between 80 and 110 keys, including ( Typing ,  numeric , function , control) keys .

Keys patterns :

1- QWERTY

known as QWERTY for its first six letters ,generally laid out in the same pattern used for typewriters, this layout helped keep mechanical typewriters’ metal arms from colliding and jamming as people typed.

2-Dvorak

The Dvorak layout places all of the vowels on the left side of the keyboard and the most common consonants on the right. The most commonly used letters are  where you place your fingers when you begin typing. People who prefer the Dvorak layout say it increases their typing speed and reduces fatigue .

3- AZERTY

AZERTY layout used in several  French-speaking countries, including France and Belgium. The French language uses several accented letters, such as é, à and ô, as well as a few other symbols such as œ that do not occur in English. A QWERTY keyboard is therefore insufficient.the swapping of letters was made to accommodate letter frequencies in French, which are different from English ones.for instance, the letter W is much rarer in French than in English, while Z is slightly more frequent.

How Keyboard works :

Keyboard has its own processor and circuitry that carries information to and from that processor.A large part of this circuitry makes up the key matrix.

The key matrix is a grid of circuits underneath the keys. In all keyboards each circuit is broken at a point below each key. When you press a key, it presses a switch, completing the circuit and allowing a tiny amount of current to flow through. The mechanical action of the switch causes some vibration, called bounce, which the processor filters out.

When the processor finds a circuit that is closed, it compares the location of that circuit on the key matrix to the character map in its  (ROM). A character map is basically a comparison chart or look up table. It tells the processor the position of each key in the matrix and what each keystroke or combination of keystrokes represents.

A computer can also use separate character maps, overriding the one found in the keyboard.