MAC OS – Unit A

Page: 10-11, 12-13

Investigating Data Processing

Understanding Memory

Data Files

Data is the information processed in a computer *words, graphics, numbers and figures*.

All data and programs are stored as files.

There are three kinds of files: A computer file is a named collection of stored data. An executable file contains the instructions that tells

a computer how to perform a certain task. A data file is created by a user, usually with

software. (Example: the report you create with word processing needs to be saved as a data file to be accessed later.)

Data Processing Binary Representation

• The characters used in human language are meaningless to a computer.

• A computer represents information as numbers called binary numbers. There are two numbers that a computer uses , “0” and “1”.

• These two numbers are called bits.• A group of 8 bits is called byte. Figure A-12, page 11• Each number should be represents with 8 bits.• Example: the number 1 is represented as 000 0001• The number 2 is represented as 000 00010

The smallest number for a computer is 0 (000 000 00) and the largest number is 255 (111 111 11)

KB, MB, GB

A kilobyte (KB) is 2024 bytes.

A megabyte (MB) is about one million bytes

A gigabyte (GB) is about one billion bytes.

A Terabyte (TB) is about one trillion bytes.

ASCII

Personal computers use the ASCII system to represent character data.

ASCII : American Standard Code for Information Interchange

Each ASCII number represents an english letter. Computers translate ASCII into binary data so that they can process it. Figure A-13, page 11

ASCII Representation

The ASCII system used 7 bits to represent the numbers 0 (000 0000) through 127 (111 1111). The numbers are for characters and non printing characters (Enter, space). The 8th bit is used for error checking.

Numbers 128 (1000 0000) through 255 (111 111 11) is used to represent additional characters and symbols. This is the extended ASCII system ex: $, ©.

Refer to figure A-13 on page 11 to study the difference between ASCII and binary digits.

Understanding Memory

One of the most important computer’s hardware is the memory, which stores instruction and data.

There are five types of memory: Random Access Memory Cache Memory Virtual Memory Read-only Memory Complementary Metal Oxide Semiconductor

Memory

SDRAM

RAM

ROM

Random Access Memory - RAM

1. Random Access Memory (RAM) temporarily stores programs and data while the computer is on to allow the computer to access these information randomly.

2. RAM doesn't’t need to access data in the same sequence in which it was stored.

3. The characters you type are stored in RAM with fonts, graphics and other objects.

4. RAM consists of chips on cards that are plugged into the motherboard.

RAM

Most personal computers use some type of synchronous dynamic access memory (SDRAM) which is synchronized with the processor to allow faster access to its contents.

RAM is referred to volatile or temporary memory because it is constantly changing as long as the computer is on and is cleared as soon as the computer is shut off.

Memory capacity is also referred to as storage capacity which is the amount of data that the computer can handle at any given time and is measured in megabytes or gigabytes.

Cache Memory

Sometime called RAM cache or CPU cache is a special, high-speed memory chip on the motherboard or CPU itself that stores frequently accessed and recently accessed data and commands.

Virtual Memory

Virtual Memory is a space on the computer’s storage devices that stimulates additional RAM.

It enables the programs to run as if your computer had more RAM by moving data and commands from RAM to the hard drive and swapping in the new data and commands.

Virtual RAM is much slower than the RAM.

Read-Only Memory - ROM

Read Only Memory is a chip on the motherboard that has been prerecorded with data.

ROM permanently stores the set of instructions that the computer uses to check the computer system’s components to make sure they are working and to activate the essential software that controls the processing functions when you turn the computer on.

ROM

ROM contains a set of instructions called BIOS (Basic Input Output System) which tells the computer to initialize the motherboard, how to recognize peripherals and to start the boot process.

Boot Process is the set of events that occurs between the moment you turn the computer on till the moment you start to use the computer.

The instructions used to execute the boot process is saved in the ROM.

ROM never changes and remains the same when the computer is turned off. Therefore, it is nonvolatile or permanent memory.

Complementary Metal Oxide Semiconductor Memory - CMOS

Complementary Metal Oxide Semiconductor Memory (CMOS) is installed on the motherboard that is activated during the boot process and identifies where essential software is stored. A small rechargeable battery powers the CMOS so its

contents are saved when the computer is turned on. CMOS changes every time you add or remove hardware on your computer system

CMOS also referred to semi permanent memory changes when the hardware is added or removed but doesn't’t empty when the computer is turned off.

Because CMOS is not cleared when the computer turns off, the data and time are stored there.

Figure A-14 page 13