4ROM Permanently stores data; non-volatile, never loses its content. ROM holds the instructions that the computer needs to operate. Data stored in ROM cannot be modified, or can be modified only slowly or with difficultyEvery computer needs some form of non-volatile storage to store the initial program that runs when the computer is powered on or otherwise begins execution (a process known as bootstrapping, often abbreviated to "booting" or "booting up").3/31/2017
5Types of ROMPROM (Programmable Read Only Memory) memories were developed at the end of the 70s by a company called Texas Instruments. These memories are chips comprising thousands of fuses (or diodes) that can be "burnt" using a device called a " ROM programmer", applying high voltage (12V) to the memory boxes to be marked. The fuses thus burnt correspond to 0 and the others to 1. 3/31/2017
6Types of ROMEPROM (Erasable Programmable Read Only Memory) memories are PROMs that can be deleted. These chips have a glass panel that lets ultra-violet rays through. When the chip is subjected to ultra-violet rays with a certain wavelength, the fuses are reconstituted, meaning that all the memory bits return to 1. This is why this type of PROM is called erasable. EEPROM (Electrically Erasable Read Only Memory memories are also erasable PROMs, but unlike EPROMs, they can be erased by a simple electric current, meaning that they can be erased even when they are in position in the computer. 3/31/2017
8Processor Computer uses two components : Memory, Processor . Processor is like the brain of the computer. Processor’s power- How many Transistors it has.Processor usually consists of one or more special chips called microprocessor.Microprocessor is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and provides results as output.3/31/2017
13How Computers Represent Data Computer processing is performed by transistors, which are switches with only two possible states: on and off.All computer data is converted to a series of binary numbers– 1 and 0. For example, you see a sentence as a collection of letters, but the computer sees each letter as a collection of 1s and 0s.If a transistor is assigned a value of 1, it is on. If it has a value of 0, it is off. A computer's transistors can be switched on and off millions of times each second.3/31/2017
15How Computers Represent Data To convert data into strings ofnumbers, computers use the binary number system.Humans use the decimal system (“deci” stands for “ten”).The binary number system works thesame way as the decimal system, buthas only two available symbols (0 and1) rather than ten (0, 1, 2, 3, 4, 5, 6, 7,8, and 9).3/31/2017
16How Computers Represent Data A single unit of data is called a bit, having a value of 1 or 0.Computers work with collections of bits, grouping them to represent larger pieces of data, such as letters of the alphabet.Eight bits make up one byte. A byte is the amount of memory needed to store one alphanumeric character.With one byte, the computer can represent one of 256different symbols or characters.3/31/2017
18How Computers Represent Data A text code is a system that uses binary numbers (1s and 0s) to represent characters understood by humans (letters and numerals).An early text code system, called EBCDIC uses eight bit codes, but is used primarily in older mainframe systems.In the most common text-code set, ASCII, each character consists of eight bits (one byte) of data. ASCII is used in nearly all personal computers.In the Unicode text-code set, each character consists of 16 bits (two bytes) of data.3/31/2017
19How Computers Represent Data EBCDIC-Extended Binary Coded Decimal Interchange Code8 bits, CharacterASCII-American Standard Code for Information Interchange8 bits, CharacterExtended ASCII8 bits, CharacterUnicode- Unicode World Wide Character Standard32 bits, 4 Billion Character3/31/2017
23The Arithmetic Logic Unit The actual manipulation of data takes place in the ALU.The ALU can perform arithmetic and logic operations.The ALU is connected to a set of registers—small memory areas in the CPU, which hold data and program instructions while they are being processed.Everything has to be broken down into these few operations.3/31/2017
25BusA bus is a path between the components of a computer. Data and instructions travel along these paths.The data bus' width determines how many bits can be transmitted between the CPU and other devices.The address bus runs only between the CPU and RAM, and carries nothing but memory addresses for the CPU to use.Peripheral devices are connected to the CPU by an expansion bus.3/31/2017
27Cache MemoryCache memory is high-speed memory that holds the most recent data and instructions that have been loaded by the CPU.Cache is located directly on the CPU or between the CPU and RAM, making it faster than normal RAM.3/31/2017
29Storage deviceComputer needs a place to keep the data and program files when they are not in use.The hardware that writes data to or reads data from astorage medium is called astorage device.RAM is like a work tableand storage is like a filecabinet.Users often confuse storagewith memory.3/31/2017
30Storage device Distinction between storage and memory: There is more room in storage than there is in memory.Contents are retained in storage when the computer is turned off, whereas the programs or data you put into memory disappear when you shut down the computer.Storage is much slower compared to memory, but also much cheaper than memory.3/31/2017
31Storage deviceThe two primary storage technologies are magnetic and optical.The primary types of magnetic storage are:Diskettes (floppy disks)Hard disksHigh-capacity floppy disksDisk cartridgesMagnetic tape3/31/2017
32Storage deviceThe two primary storage technologies are magnetic and optical.The primary types of optical storage are:Compact Disk Read-Only Memory (CD-ROM)Digital Video Disk Read-Only Memory (DVD-ROM)CD-Recordable (CD-R)CD-Rewritable (CD-RW)PhotoCD3/31/2017
33Magnetic Storage Device -How Magnetic Storage WorksA magnetic disk's medium contains iron particles, which can be polarized—given a magnetic charge—in one of two directions.Each particle's direction represents a 1 (on) or 0 (off), representing each bit of data that the CPU can recognize.A disk drive uses read/write heads containing electromagnets to create magnetic charges on the medium.3/31/2017
34Magnetic Storage Devices – Formatting Before a magnetic disk can be used, it must be formatted—a process that maps the disk's surface and determines how data will be stored.During formatting, the drive creates circular tracks around the disk's surface, then divides each track into sectors.The OS organizes sectors into groups, called clusters, then tracks each file's location according to the clusters it occupies.3/31/2017
36Magnetic Storage Devices - How OS finds Data 3/31/2017When a disk is formatted, the OS creates four areas on its surface:Boot sector – stores the master boot record, a small program that runs when you first start (boot) the computerFile allocation table (FAT) – a log that records each file's location and each sector's statusRoot folder – enables the user to store data on the disk in a logical wayData area – the portion of the disk that actually holds data
38Magnetic Storage Devices - Hard Disks 3/31/2017Hard disks use multiple platters, stacked on a spindle. Each platter has two read/write heads, one for each side.Hard disks use higher-quality media and a faster rotational speed than diskettes.Removable hard disks combine high capacitywith the convenience of diskettes.
41Optical Storage Devices – How Optical Storage Works 3/31/2017An optical disk is a high-capacity storage medium. An optical drive uses reflected light to read data.To store data, the disk's metal surface is covered with tiny dents (pits) and flat spots (lands), which cause light to be reflected differently.When an optical drive shines light into a pit, the light cannot be reflected back. This represents a bit value of 0 (off). A land reflects light back to its source, representing a bit value of 1 (on).
43Optical Storage Devices – CD-ROM 3/31/2017In PCs, the most commonly used optical storage technology is called Compact Disk Read-Only Memory (CD-ROM).A standard CD-ROM disk can store up to 650 MB of data, or about 70 minutes of audio.Once data is written to a standard CD-ROM disk, the data cannot be altered or overwritten.
44Optical Storage Devices – DVD-ROM 3/31/2017A variation of CD-ROM is called Digital Video Disk Read-Only Memory (DVD-ROM), and is being used in place of CD-ROM in many newer PCs.Standard DVD disks store up to 9.4 GB of data—enough to store an entire movie. Dual-layer DVD disks can store up to 17 GB.DVD disks can store so much data because both sides of the disk are used, along with sophisticated data compression technologies.