Teacher: Ms. LuceName: Alex H.Date: February 18th 2010Course: TEJ3M

http://computer.howstuffworks.com/computer-memory4.htm

Memory is Data. Memory can be stored in devices meaning programs or data. Memory is what you save and you can use later on. There are two types of main memory that we see in everyday life on computers. These are called RAM and ROM. Also known as Random access memory and Read-Only memory. There are many strands that they branch off to. Memory is also transferred in different ways and can be deleted.

Picture of RAM above

Primary Digital Memory branches off into RAM and ROM. RAM standing for Random Access Memory for things such as a Cameras when you are taking off photos or editing them. RAM is also known as temporary memory because if you don't save it somewhere else, the memory in RAM will be deleted once the computer is turned off. ROM is Read Only Memory and it is for programs or data that the computer needs to program or function properly. It is also called Permanent data because it is any instructions or data that determines how a computer boots or functions.

RAM is Random Access Memory, It is temporary memory in a computer. RAM is slots and the OS(Operating system) is loaded to RAM when the PC is turned on. An example of RAM is when you are taking data from a camera and you load it to see the pictures and you save it in RAM. Once you turn off the computer, all the memory in RAM is deleted. That is why you should store data on USBs or Cds so you do not lose your information.

There are many different types of RAM but two main types are SRAM and DRAM. SRAM stands for Static Random Access Memory, It is more expensive than DRAM which is Dynamic Random Access Memory. SRAM is more of a single chip because you really don't need that much of it. SRAM is more expensive than DRAM because SRAM does not need to be periodically refreshed every few milliseconds such as DRAM needs to be. Other examples of RAM are SDRAM SDRAM RDRAM DDR-RAMSDRAM RDRAM SLDRAM.

An Example of DRAM above

How SRAM works is that it stores each bit as a voltage, each memory cell requires 6 transistors therefore giving low chip density and high speed.

DRAM is very simplistic compared to SRAM since it has to be refreshed constantly, only one transistor and a capacitor is needed. The information leaks and needs to be read and written every few milliseconds(refreshing the memory).

ROM is Read-Only Memory, also known as permanent memory. It is permanent because it is data or programs that determine how the computer boots and functions. It is a chip and it can be either a square or rectangular. The memory in ROM is unchangeable or requires a special operation to change it. ROM uses a diode to connect the lines if the value is 1. If the value is 0, then the lines are not connected at all.

One type of ROM is PROM which is Programmable Read-Only memory. Blank PROM chips are cheap and can be bought and programmed with a special tool called a programmer, hence the name. Every intersection of a column and row in a PROM chip has a fuse connecting them. A charge sent through a column will pass through the fuse in a cell to a grounded row indicating a value of 1. Since all of the cells have a fuse, when the PROM is blank the initial state is all 1's, to make it zero, you use the programmer to send a calculated current to the cell. PROM can only be programmed once.

Another type is EEPROM, also known as Electrically erasable programmable read-only memory. Unlike EPROM this chip does not need to be removed to be rewritten. All the data does not need to be erased to change a part of the memory. Changing the contents does not require additional dedicated equipment. you can return the electrons in the cells of an EEPROM to normal with an electrical field to each cell. By doing this, you can erase the cells which u want to rewrite. EEPROMS are changed 1 byte a time which is really slow.

Another type of ROM is EPROM it is also known as Erasable programmable read-only memory. They are cheap per chip but the cost builds up. Unlike ROM, EPROM can be programmed many times, hence the name. Erasing an EPROM requires a special tool that emits a specific amount of UV light. The cell at each intersection has two transistors. The two transistors are separated by a thin oxide layer. One of the transistors is known as the floating gate and the other as the control gate. The floating gate's only link to the row is through the control gate. While the link is connected, the value is one to change it to 1 you must use Fowler-Nordheim tunnelling This is a process where alter the placement of electrons in the floating gate. A blank EPROM has all the values as 0.

The last of the 5 basic ROMs is Flash Memory, it is a type of EEPROM but it is faster because it writes data in blocks which are bigger in which the EEPROM does it in. It uses in-circuit wiring to erase by using an electrical field. Some examples of Flash Memory are a memory stick, Memory cards, Your computers BIOS chip etc.

Memory address is when a byte has an address according to its memory. That place where the byte is stored is called the memory address. At that address is the information that the CPU needs for whatever reason.

Memory size is essential for how much data or programs you would like to store into your device, be it your P.C, phone or even MP3. Most people round our numbers such as a megabyte to 1million bytes because the actual size is close to 1 million. Here are the rounded numbers of the memory sizes.

-Byte- 8 bits-smallest piece of memory

(also nibble= 1/2 byte (4 bits)

word= 2 bytes(16 bits))

Kilo-1000

Mega- 1,000,000

Giga- 1,000,000,000

Tera-1 trillion

As you can see they all end with a 0, therefore they are all rounded. They are rounded because it is put in easier terms and is calculated easier. But there are actual sizes and they are a little bit more than the actual sizes because the actual sizes were rounded down.

kilo- 1 024

Mega- 1 048 576

Giga- 1 073 741 824

Tera- 1 099 511 627 776

peta- 1 125 899 906 842 624

exa- 1 152 921 504 606 846 876

zetta- 1 180 591 620 717 411 303 424

Yotta- 1 208 925 819 614 629 174 706 176

Some examples of devices that store memory are Punch Card memory, Magnetic Core memory and Semi Conductor memory. There are many different devices that store memory but these ones are major memory devices.

Punch Card Memory is pretty much the title as it is the process of storing information but punching holes into a card in specific locations. Punched cards were used to input and output information on the first generation of computers. These cars were also used for storing instructions which were pretty much the first form of computers.

Semi Conductor Memory is used by all digital computers. This type of memory is based on integrated circuitry technology. It is faster and cheaper than what they used before, core memory. Semiconductor memory has latches and the latches are able to store data for an indefinite amount of time.

A process called Caching greatly increases the speed of pulling bits and bytes from memory. When you use a cache, you must check it to see if what you are looking for is in there. If it is there it is a cache hit and if not, a cache miss and the computer has to search the larger area of memory and it takes a while. There can be plenty layers of cache.

L1 caching is when the computer uses the microprocessor. They build a system directly into the microprocessor and the memory transfers at the speed of a microprocessor and not as slow as a bus. The microprocessor is the fastest thing in the computer.

L2 caching is when there are three layers and the computer can check those 3 layers. It can also be called a two-level cache. It transfers at the speed of a bus.

Registers are Small amounts of memory attached to the CPU(Central Processing Unit). The memory attached to the CPU is an essential data for the CPU. Some Examples are a 32 bit processor and a 64 bit processor.

Thanx for watching.By: Alex Huang