What is a Computer? A device that can run under specific directions What is a Program? –A specific set of instructions given to the computer –Requires a specific language to communicate –Done by a programmer Software vs. Hardware –Software = Programs –Hardware=Components of Computer such as monitors, printers, keyboard Computer Structure 3 Main Components CPU – Central Processing Unit Memory – High Speed Memory Unit I/O – Input/Output Devices

Memory Unit (Main Memory / Physical Purpose –Stores all the instructions used by the CPU –Stores all the data used by the CPU Construction –Made up of metal oxide on Silicon (This memory is also called Random Access Memory, not to be confused with ROM which stands for Read Only Memory) Building Block –Made up of logical units of same size –Most common unit is BYTE –Byte divides into BITS (Binary Digits) BIT –Is an electronic unit that can be magnetized to store 1 or 0 or can have ON or OFF state

Construction of a Byte –8 Bits make up a Byte. The bits should be consecutive Representation of a BIT/BYTE –Magnetized to produce or 1 Byte –Right Most BitLeast Significant Bit (LSB) –Left Most BitMost Significant Bit (MSB) –Each Bit can be ON or OFF –Magnetized states are contents of a bit/byte 10

Possible ON/OFF states for a Byte For one bit we can have 2 1 For two bits how many possibilities can there be?

For three bits then there would be 2 3 For N bits, we have 2 N And for a byte there will be 2 8 number of values

Grouping of Bits/Bytes The following naming conventions are manufacturer dependent 4 consecutive bits1 Nibble 8 consecutive bits1 Byte 2 consecutive bytes1 word 4 consecutive bytes1 longword 8 consecutive bytes1 quadword 10 consecutive bytes1 octaword Identifying a Byte –Address: Special concept that identifies a byte –Extra bits are assigned to every byte to represent its address –For every PROGRAM an ADDRESS SPACE is assigned

ADDRESS SPACE It is a set of all unique addresses that a program can reference Size of Address Space –Number of bits that an address space uses is the size of the address space –If N bits are used up for address space than size will 2 N N-1 ……………………………………… 1 0

Address Contents of a Byte Address for each Byte never changes Contents of a byte change