3.14 Bits, Bytes and Binary

How many bits is a nibble?

4 bits

How many bits is a byte?

8 bits

Kibibyte

2¹⁰ = 1024

Mebibyte

2²⁰

Gibibyte

2³⁰

Tebibyte

2⁴⁰

Pebibyte

2⁵⁰

Exibyte

2⁶⁰

Zebibyte

2⁷⁰

Yobibyte

2⁸⁰

Kilobyte

10³

Megabyte

10⁶

Gigabyte

10⁹

Terabyte

10¹²

Petabyte

10¹⁵

Exabyte

10¹⁸

Zettabyte

10²¹

Yottabyte

10²⁴

How many bits did ASCII use?

7 bits

How would Cat be stored with ASCII? A=065, a=097, z=122

C: 067
a: 097
t: 116

Why is the number character not the same as the actual number value? e.g ‘7’ and 7?

Because the ASCII value of ‘7’ is 55, not 7, therefore 7 + '7' = 62 and not 14.

Why was Unicode introduced?

To provide a universal character encoding standard that could represent characters from all the world's writing systems in a single standard.

How was compatibility with ASCII and Unicode maintained?

The first 128 codes remained the same in Unicode as ASCII.

How many bits does UTF-16 encoding use?

16 bits.

What’s a disadvantage of using Unicode?

• Increased file size

• Increased transmission time

What’s a parity bit?

An additional bit that is used to check that the other bits transmitted are likely to be correct.

How does odd parity determine if the received bits are likely to be correct?

There should be odd number of 1s including the parity bit.

How does odd parity determine if the received bits are likely to be correct?

There should be even number of 1s including the parity bit.

What should the parity bit set to for 0010110 using odd parity?

0

How does majority voting work?

• Each bit is sent three times.

• If a bit value is changed during transmission, the recipient would use the majority rule

• and assume that the other two bits have not changed and therefore correct

What’s a disadvantage of majority voting?

Triple the volume of data is sent.

How could a parity bit system potentially fail?

If two bits are flipped erroneously during transmission, the total number of 1s will still be even/odd.

How does a checksum detect errors?

1. A mathematical algorithm is applied to a unit of data which creates a checksum value

2. Checksum value transmitted with the unit of data

3. Same algorithm applied on recipient device on received data

4. If checksums are the same, data has been transmitted correctly

How does a check digit detect errors?

1. A mathematical algorithm is applied to all digits except the check digit, producing a calculated value

2. This value is compared to the check digit (the last digit)

3. If they match, no error is detected; if they differ, an error has occurred and the data is rejected