Memory and Storage and a little bit.

Types of Memory RAM (Random access memory )  (RAM) is the best known form of computer memory. RAM is considered "random access" because you can access any memory cell directly if you know the row and column that intersect at that cell.  When a computer is powered on, certain operating system files (such as MS XP files) load into RAM from the hard disk. These files remain in RAM as long as the computer has continuous power.

RAM Continued Think of RAM as the workspace on top of your desk. Just as the top of your desk needs a certain amount of space to hold papers, a computer needs a certain amount of memory to store programs, data and information. The more RAM a computer has the faster the computer it will respond.

Types of RAM DRAM (Dynamic) RAM  Chips must be re-energized constantly or they will lose their contents SDRAM (Synchronous) DRAM  Chips are much faster than DRAM because they are synchronized to the system clock. DDR (Double Data Rate) SDRAM  Even faster than SDRAM because they transfer data twice for each clock cycle SRAM (Static) RAM  Chips do not need be re-energized as much as DRAM and are therefore faster and more reliable. They are also far more expensive.

Device Typical Access Time Static RAM (SRAM) 5-15 nanoseconds Dynamic RAM (DRAM) nanoseconds Hard disk drive 6-12 milliseconds CD-ROM Drive milliseconds Access time is the speed at which data is retrieved by the storage device

ROM (Read Only Memory) Read-only memory (ROM), also known as firmware, is an integrated circuit programmed with specific data when it is manufactured. ROM chips are used not only in computers, but in most other electronic items as well. ROM Types There are five basic ROM types: ROM PROM EPROM EEPROM Flash memory

ROM Continued Data stored in these chips is non-volatile it is not lost when power is removed. Data stored in these chips is either unchangeable or requires a special operation to change (unlike RAM, which can be changed as easily as it is read). This means that removing the power source from the chip will not cause it to lose any data.

BIOS (basic input/output system) One of the most common uses of Flash memory is for the basic input/output system of your computer, commonly known as the BIOS (pronounced "bye- ose"). On virtually every computer available, the BIOS makes sure all the other chips, hard drives, ports and CPU function together.

Types of Storage Devices Floppy disks.  Double density (DD) disks offer up too 800K  High density (HD) disks offer up to 1.44MB  Advantages Robust Universal Portable Protected  Disadvantages Limited Capacity

Floppy Don’ts

Zip Drive A "zip drive" is basically just a piece of hardware that reads disks that are a bit chunkier in size than that of a floppy disk. How much memory each disk holds can vary but it's about 100Mb.

CD ROM Drive CDs can hold up to 680Mb and most machines nowadays come equipped with a cd writer. This is simply a piece of hardware that lets you read information from a CD and then write information onto a CD as well.

CD Don’ts Stack discs Touch the underside of the disc Write on the label side of the disc Expose the disc to excessive heat or sunlight Eat, drink or smoke near a disc

Magnetic Tape These are larger storage devices that are generally used in servers as file back-up media. They are like standard audio tape cassettes but have the ability to store a lot more information. They hold up to 24Gb

USB (Pen) Drive A small, portable flash memory card that plugs into a computer’s USB port and functions as a portable hard drive with up to 2GB of storage capacity. USB flash drives are touted as being easy-to- use as they are small enough to be carried in a pocket and can plug into any computer with a USB drive. USB flash drives have less storage capacity than an external hard drive, but they are smaller and more durable because they do not contain any internal moving parts.

Hard Disks A magnetic disk on which you can store computer data. The term hard is used to distinguish it from a soft, or floppy, disk. Hard disks hold more data and are faster than floppy disks. A hard disk, for example, can store anywhere from 10 to more than 100 gigabytes A single hard disk usually consists of several platters. Each platter requires two read/write heads, one for each side. All the read/write heads are attached to a single access arm so that they cannot move independently.

Hard Disks Continued Hard disks and cassette tapes also share the major benefits of magnetic storage -- the magnetic medium can be easily erased and rewritten, and it will "remember" the magnetic flux patterns stored onto the medium for many years. The tape in a cassette-tape deck moves over the head at about 2 inches (about 5.08 cm) per second. The information on a hard disk is stored in extremely small magnetic domains compared to a cassette tape's. The size of these domains is made possible by the precision of the platter and the speed of the medium.

Hard disks Continued A hard-disk platter can spin underneath its head at speeds up to 3,000 inches per second (about 170 mph or 272 kph)! Data is stored onto the disk in the form of files. A file is simply a named collection of bytes.

Bits & Bytes In the world of computers, information is digital. This information is made up of discrete units. These discrete units are called: Bits. Bit: (Binary digit) is the smallest unit of information a computer can process Bits have only two values: 1 or 0 A collection of 8 bits is called a byte. Bytes are bigger than bits.

Bytes cont… A collection of 8 bits can represent 256 different messages: 2 8 = 256 By mixing and matching combinations of “On’s” and “Off’s” you can get 256 different messages.

Examples = 0

Examples = 1

Examples = 2

Examples = 3

Examples = 4

Examples = 10

Examples = 255 Note: we get 256 possible characters because we start at 0 and go to 255 which is 256 separate numbers.

ASCII To make words, sentences, and paragraphs fit into the computer’s binary- code circuitry, a unique piece of code was devised to represent each letter, digit, and special character as a unique string of bits. ASCII (pronounced as-kee) is the most widely used code

ASCII American Standard Code Using only 8 bits ASCII has a set of 256 individual characters, for all letters (upper and lower case), numbers and some special characters Unicode is possibly going to replace ASCII. Unicode has a 65,000 character set. This will be done by using 2 bytes (16 bits) per character.

Instructions using Binary Bits can represent data stored on a computer. A string of bits can also represent an instruction  could tell the CPU to add two numbers together. More on this shortly…

Special Modifier Terms TermValue ByteA group of 8 bits. K (kilobyte) also KB About 1000 bytes of information. Technically 1K is 1024, because 1024 is 2 10 MB (megabyte)Approximately 1000K, or 1 million bytes GB (gigabyte)Approximately 1000MB TB (terabyte)Approximately 1 million megabytes.

The End…