Unlock your potential with these comprehensive and concise Computer Science IGCSE Revision Notes. Covering the entire syllabus, these notes simplify complex topics for you - with well organized and structured notes - include illustrative diagrams, and focuses on main points for your exam. Perfect f...
The maximum denary of an 8-bit binary number is (2^8-1) = 255
The generation of a 9th bit number is a clear indication that it has exceeded its value
This is known as an overflow error and in this case is an indication that a number is too big to be stored in the
computer using 8 bits
You can use a larger number of bits to store very large values, for example, 16 bits is 65,536 maximum denary
value
Use of binary registers
Can be used to store data
Can be used to store instructions
Logical Binary Shifts
L.O: To solve problems using binary multiplication and logical binary shifts
The logical shift means moving the binary number to the left or to the right
Each shift left is equivalent to multiplying the binary number by 2
Each shift right is equivalent to dividing the binary number by 2
As bits are shifted, any empty positions are replaced with a zero
The denary number 21 is 00010101 in binary. If we put this into an 8-bit register:
If we now shift the bits in this register one place to the left, we obtain:
Notice how the empty right-most bit position is now filled with a 0
128 64 32 16 8 4 2 1
0 0 1 0 1 0 1 0
128 64 32 16 8 4 2 1
0 0 0 1 0 1 0 1
The left-most bit is often referred to as the MOST SIGNIFICANT BIT, and now here, the left-most bit is now lost
following a left shift
If the left-most 1-bit has been lost in the 8-bit register, this error is because we have exceeded the maximum
number of left shifts possible using this register
The value of the binary bits is now 21 x 2^1 (41). Similarly if you shift the original number two places, 21 x 2^2 (41 x
2)
Computer Science IGCSE Revision Notes 4
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