Bits and Bytes

 

Bits

Computers consist of millions of interconnected circuits and switches. In order for something to happen, switches need to be moved into different positions to aid in the creation of a circuit or path. A computer needs to be given instructions in the form of a code that tells the switches to turn on or off. On is represented by a 1 and off by a 0. This is known as the binary system. A single unit (1 or 0) is called a Binary Digit but is more commonly known as a bit (b). One bit on its own doesn’t provide much information therefor it’s only when several bits are strung together that a computer can do anything meaningful. Two bits (0 and 1) can be joined to give four separate on/off instructions (00, 11, 10 and 01).

Bytes

So that you can enter words into a computer and it can show you what it is doing in a way you that you understand, all the characters of a language must be represented by a code. By the time all the different characters in upper and lower cases, numbers, punctuation marks and accents are accounted for, more than two hundred separate pieces of information are required. Each character is represented by an 8 bit Code Number. There are 256 different Code Numbers because that is the maximum number of configurations that eight 0s or 1s can make. Eight bits are called a byte thus one Byte represents a single character.

A = 01000001

a = 01100001

b = 01100010

1 = 00110001

8 bits = 1 byte ( B )

1,024 bytes = 1 kilobyte ( kB )

1,024 kilobytes = 1 megabyte ( MB ) or 1,048,576 bytes

1,024 megabytes = 1 gigabyte ( GB ) or 1,073,741,824 bytes

1,024 gigabytes = 1 terabyte ( TB ) or 1,099,511,627,776 bytes

 

Memory - RAM and ROM

A computer needs to be able to remember what its user inputs. It transfers data from temporary memory to a more permanent storage so that you can retrieve your work in the future. Computers use two kinds of memory, temporary and permanent. Temporary Memory is known as Random Access Memory (RAM) and Permanent Memory is known as Read-Only Memory (ROM).

ROM is a microchip that stores information that can only be read and is always available. The data stored in ROM provides diagnostic routines that occur each time the computer is switched on and part of a system software called the Toolbox that provides information that programmers can use when they create applications for a computer. In some modern computers the ROM chip has been replaced by Flash Memory; this can be written to, read, updated and even erased.

RAM is the temporary memory of a computer. It is lost when the system is shut down and switched off. RAM needs power (an electric current) to retain information. When you open a program you are effectively copying parts of it into RAM to enable you to see and use it. When you draw or type on screen it isn’t permanent until it is saved onto a storage device so it is important to save work regularly. RAM uses chips called Single In-Line Memory Modules (SIMMs) or Dual In-Line Memory Modules (DIMMs). The greater the capacity of SIMMs/DIMMs, the more you can achieve in RAM meaning you can work on larger and more complex images.

There is a second kind of RAM called PRAM (Parameter RAM). Settings such as the Time and Date are stored here. Unlike RAM, data stored in PRAM isn’t lost when a computer is switched off because it has its own battery; if the battery were removed, the data would be lost.

Storage

There are many different types of storage devices available for computers these days. The most common that every computer has is a Hard Disk Drive (HDD). The HDD is where a computers operating system is stored. Other storage devices include; Compact Disk (CD), Digital Versatile Disk (DVD), USB Flash Drive, Floppy Disk (out dated), ZIP Disk (also out dated) and Flash Memory Cards such as Secure Digital (SD) and Compact Flash (CF). Copying work from RAM to storage is called Saving. You save work by navigating to the File menu in the menu bar and selecting the Save command.

A typical HDD consists of several disks called Platters, these are sealed in a dust-free box. There is a HDD inside every computer (internal) but they can also be mounted inside a free-standing box/caddy) with a separate power supply (external). The Platters are made of a rigid substrate which is coated with magnetised iron oxide particles. These particles are aligned in one of two directions (0 or 1) by a read-write head which changes their polarity by transmitting a magnetic field as the platter spins beneath it. Data is written to and read from different parts of the platter by the head as it oscillates rapidly back and forth.