I come across the below statement while studying about HTML Character Sets and Character Encoding :
Since ASCII used 7 bits for the character, it could only represent 128
different characters.
When we convert any decimal value from the ASCII character set to its binary equivalent it comes down to a 7-bits long binary number.
E.g. For Capital English Letter 'E' the decimal value of 69 exists in ASCII table. If we convert '69' to it's binary equivalent it comes down to the 7-bits long binary number 1000101
Then, why in the ASCII Table it's been mentioned as a 8-bits long binary number 01000101 instead of a 7-bits long binary number 1000101 ?
This is contradictory to the statement
Since ASCII used 7 bits for the character, it could only represent 128
different characters.
The above statement is saying that ASCII used 7 bits for the character.
Please clear my confusion about considering the binary equivalent of a decimal value. Whether should I consider a 7-bits long binary equivalent or a 8-bits long binary equivalent of any decimal value from the ASCII Table? Please explain to me in an easy to understand language.
Again, consider the below statement :
Since ASCII used 7 bits for the character, it could only represent 128
different characters.
According to the above statement how does the number of characters(128) that ASCII supports relates to the fact that ASCII uses 7 bits to represent any character?
Please clear the confusion.
Thank You.
In most processors, memory is byte-addressable and not bit-addressable. That is, a memory address gives the location of an 8-bit value. So, almost all data is manipulated in multiples of 8 bits at a time.
If we were to store a value that has by its nature only 7 bits, we would very often use one byte per value. If the data is a sequence of such values, as text might be, we would still use one byte per value to make counting, sizing, indexing and iterating easier.
When we describe the value of a byte, we often show all of its bits, either in binary or hexadecimal. If a value is some sort of integer (say of 1, 2, 4, or 8 bytes) and its decimal representation would be more understandable, we would write the decimal digits for the whole integer. But in those cases, we might lose the concept of how many bytes it is.
BTW—HTML doesn't have anything to do with ASCII. And, Extended ASCII isn't one encoding. The fundamental rule of character encodings is to read (decode) with the encoding the text was written (encoded) with. So, a communication consists of the transferring of bytes and a shared understanding of the character encoding. (That makes saying "Extended ASCII" so inadequate as to be nearly useless.)
An HTML document represents a sequence of Unicode characters. So, one of the Unicode character encodings (UTF-8) is the most common encoding for an HTML document. Regardless, after it is read, the result is Unicode. An HTML document could be encoded in ASCII but, why do that? If you did know it was ASCII, you could just as easily know that it's UTF-8.
Outside of HTML, ASCII is used billions—if not trillions—of times per second. But, unless you know exactly how it pertains to your work, forget about it, you probably aren't using ASCII.
Related
I'm using RISC-V and I am limited to using just and, or, xori, addition, subtraction, multiplication, division of integer values.
So for instance, the letter "a" will be represented as 97 and "aa" will be represented as 24929, and so on. The UI converts binary sequence into decimal representation, and I cannot directly modify n-th bit.
Is there anyway I can find a simple, general equation of converting from lowercase to uppercase the decimal representation of a maximum of 8 letter sequence of Strings?
Also, I forgot to add, I can't partition the string into individual letters either. Maybe it's possible, but I don't know how to do it.
Letters or characters are usually represented as byte values, which are easier to read in hexadecimal. This can be seen if you convert 97 and 24929 to hex.
You did not mention the system which was used to encode the characters; mentioning the value for one character is not definitive. Assuming your letters are encoded as ASCII, find an ASCII table and figure out the DIFFERENCE between upper- and lowercase character codes.
Use this knowledge to design an algorithm to transform lowercase character codes to uppercase.
A good uppercase conversion algorithm will not modify characters that are not lowercase letters.
This can be extended to SIMD if you are careful to avoid carries between bytes if you need to add or subtract.
After reading the documentation, I understood that there is a one-byte or two-byte length prefix to a varying character so as to determine its length. I understand too that, for a varchar, each character might have a different length in bytes depending on the character itself.
So my question is:
How does the DBMS determine each character's length after it's stored?
Meaning: After a string is stored, let's say it's 4 characters long, and let's suppose that the first character is 1 byte long, the second 2 bytes, the 3rd 3 bytes and the 4th is 4..
How does the DB know how long is each character when retrieving the string so as to read it correctly?
I hope the question is clear, sorry for any English mistakes I made. Thanks
The way UTF-8 works as a variable-length encoding is that the 1-byte characters can only use 7 bits of that byte.
If the high bit is 0, then the byte is a 1-byte character (which happens to be encoded in the same way as the 128 ASCII characters).
If the high bit is 1, then it's a multi-byte character.
Picture from https://en.wikipedia.org/wiki/UTF-8
If you're talking about UTF-8, that's not quite how it works. It uses the highest bit in each byte to indicate that the character continues into the next byte, and can store one, two, three or four byte characters fairly efficiently. This is in contrast to UTF-32 where every character is automatically four bytes, something that is obviously very wasteful for some types of text.
When using UTF-8, or any character set where the characters are a variable number of bytes, there's a disconnect between the length of the string in bytes and the length of the string in characters. In a fixed-length system like Latin1, which is rigidly 8-bit, there's no such drift.
Internally the database is most concerned with the length of a field in terms of bytes. The length in terms of characters is only explicitly exposed when calling functions like LENGTH(), as otherwise it's just a bunch of bytes that, if necessary, can be interpreted as a string.
Historically speaking the database stored the length of a field in bytes in a single byte, then the data itself. That's why VARCHAR(255) is so prevalent: It's the longest string you can represent with a single byte length field. Newer databases like Postgres allow >2GB character fields, so they're using four or more bytes to represent the length.
I was just curious because 65 is the same as the letter A
If this is the wrong stack sorry.
"65 is the same as the letter A": It is true if you say it is. But not saying more than that isn't very useful.
There is no text but encoded text. There are no numbers but encoded numbers. To the CPU, some number encodings are native, everything else is just undifferentiated data.
(Some data is just data for programs, other data is the CPU instructions of programs. It's a security problem if a CPU executes data as instructions inappropriately. Some architectures keep program data and instructions separate.)
Common native number encodings are signed and unsigned integers of 1, 2, 4, and 8 bytes and IEEE-754 single and double precision floating point numbers. Signed integers are usually two's-complement. Multi-byte integers have a byte ordering (or endianness) because on typical machines each byte is individually addressable. If a number encoding is not native, a program library is needed to process such data.
Text is a sequence of encoded characters from a character set. There are hundreds of character sets. A character set is an assignment of a conceptual character to a number called a codepoint. Sometimes the conceptual characters are categorized as lowercase letter, digit, symbol, etc. A codepoint value is mapped to bytes using a character encoding. Most character sets have one encoding, but Unicode has several. Some character sets are subsets of other character sets—such relationships are not generally useful because exactly one character set is used in any one context.
A program is a set of instructions that operate on data. It must apply the correct operations to the right data. So, it is the program that differentiates between text and number, usually by its location or flow path.
Stored data must be in a known layout of encoded text and numbers. Sometimes the layout is stored also. The layout is called metadata. Without the metadata accompanying the data, or being agreed upon, the data cannot be used.
It's all quite simple with appropriate bookkeeping. But there are several methods of bookkeeping so there is no general solution to how to handle data without metadata. Methods include: Well-known and/or registered file extensions, HTTP headers, MIME types, HTML meta charset tag, XML encoding declaration. Some methods only work in a certain context, such as audio/video codecs having a four-character code (FourCC), and unix shell scripts with a shebang. Some methods only help narrow guessing, such as file signatures. Needless to say, guessing should be avoided; it leads to security issues and data loss.
Unfortunately, text files are often without metadata. It is particularly important to agree upon or separately communicate the metadata.
Data without metadata is "binary". So the writer of text must agree with the reader on which character encoding is to be used. Similarly, for all types of data. Here reader and writer are both humans and programs.
Short answer. They don't. Longer answer, every binary combination between 00000000 and 11111111 has a character representation in the ASCII character set. 01000001 just happens to be the first capital letter in the Latin alphabet that was designated over 30 years ago. There are other character sets, and code pages that represent different letter, numbers, non-printable and accented letters. It's entirely possible that the binary 01000001 could be a lower case z with a tilde over the top in a different character set. 'computers' don't know (or care) what a particular binary representation means to humans.
What is the difference between 65 and the letter A in binary as both represent same bit level information?
Basically, a computer only understand numbers, and not every numbers: it only understand binary represented numbers, ie. which can be represented using only two different states (for example, 1 and 2, 0V and 5V, open and close, true or false, etc.).
Unfortunately, we poor humans doesn't really like reading zeros and ones... So, we have created some codes, to use number like if they were characters: one of them is called ASCII (American Standard Code for Information Interchange), but there is also some others, such as Unicode. The principle is simple: all the program have to do is manipulating numbers, what any CPU does very well, but, when it comes to displaying these data, the display represent them as real characters, such as 'A', '4', '#', or even a space or a newline.
Now, as soon as you are using ASCII, the number 65 will represent the letter 'A'. All is a question of representation: for example, the binary number 0bOOOO1111, the hexadecimal one 0x0F, the octal one 017 and the decimal number 15 all represent the same number. It's the same for letter 'A': think of ASCII as a base, but instead of using the base 2 (binary), 8(octal), 10(decimal) or 16(hexadecimal), to display numbers, it's used in a complete different manner.
To answer your question: ASCII 'A' is hexadecimal 0x41 is decimal 65 is octal 0101 is binary 0b01000001.
Every character is represented by a number. The mapping between numbers and characters is called encoding. Many encodings use for the letter A the number 65. Since in memory there are no special cells for characters or numbers, they are represented the same way, but the interpretation in any program could be very different.
I may be misunderstanding the question and if so I apologise for getting it wrong
But if I'm right I believe your asking what's the difference between a char and int in binary representation of the value 65 which is the ascii decimal value for the letter A (in capital form)
First off we need to appreciate data types which reserve blocks of memory in the ram modules
An interget is usually 16 bits or more if a float or long (in c# this declaration is made by stating uint16, int16, or int32, uint32 so on, so forth)
A character is an 8 bit memory block
Therefore the binary would appear as follows
A byte (8 bits) - char
Decimal: 128, 64, 32, 16, 8, 4, 2, 1
Binary: 01000001
2 bytes (16 bit) - int16
Binary; 0000000001000001
Its all down to the size of the memory block reserved based on the data type in the variable declaration
I'd of done the decimal calculations for the 2 bit but I'm on the bus at the moment
First of all, the difference can be in size of the memory (8bits, 16bits or 32bits). This question: bytes of a string in java
Secondly, to store letter 'A' you can have different encodings and different interpretation of memory. The ASCII character of 'A' in C can occupy exact one byte (7bits + an unused sign bit) and it has exact same binary value as 65 in char integer. But the bitwise interpretation of numbers and characters are not always the same. Just consider that you can store signed values in 8bits. This question: what is an unsigned char
How to convert alphabet to binary? I search on Google and it says that first convert alphabet to its ASCII numeric value and than convert the numeric value to binary. Is there any other way to convert ?
And if that's the only way than is the binary value of "A" and 65 are same?
BECAUSE ASCII vale of 'A'=65 and when converted to binary its 01000001
AND 65 =01000001
That is indeed the way which text is converted to binary.
And to answer your second question, yes it is true that the binary value of A and 65 are the same. If you are wondering how CPU distinguishes between "A" and "65" in that case, you should know that it doesn't. It is up to your operating system and program to distinguish how to treat the data at hand. For instance, say your memory looked like the following starting at 0 on the left and incrementing right:
00000001 00001111 000000001 01100110
This binary data could mean anything, and only has a meaning in the context of whatever program it is in. In a given program, you could have it be read as:
1. An integer, in which case you'll get one number.
2. Character data, in which case you'll output 4 ASCII characters.
In short, binary is read by CPUs, which do not understand the context of anything and simply execute whatever they are given. It is up to your program/OS to specify instructions in order for data to be handled properly.
Thus, converting the alphabet to binary is dependent on the program in which you are doing so, and outside the context of a program/OS converting the alphabet to binary is really the exact same thing as converting a sequence of numbers to binary, as far as a CPU is concerned.
Number 65 in decimal is 0100 0001 in binary and it refers to letter A in binary alphabet table (ASCII) https://www.bin-dec-hex.com/binary-alphabet-the-alphabet-letters-in-binary. The easiest way to convert alphabet to binary is to use some online converter or you can do it manually with binary alphabet table.