I know that this question may sound stupid, but let me just explain. So...
Everyone knows that byte is 8 bits. Simple, right? But where exactly is it specified? I mean, phisically you don't really use bytes, but bits. For example drives. As I understand, it's just a reaaaaly long string of ones and zeros and NOT bytes. Sure, there are sectors, but, as far as I know, there are programmed at software level (at least in SSDs, I think). Also RAM, which is again - a long stream of ones and zeros. Another example is CPU. It doesn't process 8 bits at a time, but only one.
So where exactly is it specified? Or is it just general rule, which everyone follows? If so, could I make system (either operating system or even something at lower level) that would use, let's say, 9 bits in a byte? Or I wouldn't have to? Also - why can't you use less than a byte of memory? Or maybe you can? For example: is it possible for two applications to use the same byte (e.g. first one uses 4 bits and second one uses other 4)? And last, but not least - does computer drives really use bytes? Or is it that, for example, bits 1-8 belong to something, next to them there are some 3 random bits and bits 12-20 belong to something different?
I know that there are a lot of question and knowing answers to these questions doesn't change anything, but I was just wondering.
EDIT: Ok, I might've expressed myself not clear enough. I know that byte is just a concept (well, even bit is just a concept that we make real). I'm NOT asking why there are 8 bits in byte and why bytes exist as a term. What I'm asking is where in a computer is byte defined or if it even is defined. If bytes really are defined somewhere, at what level (a hardware level, OS level, programming language level or just at application level)? I'm also asking if computers even care about bytes (in that concept that we've made real), if they use bytes constantly (like in between two bytes, can there be some 3 random bits?).
Yes, they’re real insofaras they have a definition and a standardised use/understanding. The Wikipedia article for byte says:
The modern de-facto standard of eight bits, as documented in ISO/IEC 2382-1:1993, is a convenient power of two permitting the values 0 through 255 for one byte (2 in power of 8 = 256, where zero signifies a number as well).[7] The international standard IEC 80000-13 codified this common meaning. Many types of applications use information representable in eight or fewer bits and processor designers optimize for this common usage. The popularity of major commercial computing architectures has aided in the ubiquitous acceptance of the eight-bit size.[8] Modern architectures typically use 32- or 64-bit words, built of four or eight bytes
The full article is probably worth reading. No one set out stall 50+ years ago, banged a fist on the desk and said ‘a byte shallt be 8 bits’ but it became that way over time, with popular microprocessors being able to carry out operations on 8 bits at a time. Subsequent processor architectures carry out ops on multiples of this. While I’m sure intel could make their next chip a 100bit capable one, I think the next bitness revolution we’ll encounter will be 128
Everyone knows that byte is 8 bits?
These days, yes
But where exactly is it specified?
See above for the ISO code
I mean, phisically you don't really use bytes, but bits.
Physically we don’t use bits either, but a threshold of detectable magnetic field strength on a rust coated sheet of aluminium, or an amount of electrical charge storage
As I understand, it's just a reaaaaly long string of ones and zeros and NOT bytes.
True, everything to a computer is a really long stream of 0 and 1. What is important in defining anything else is where to stop counting this group of 0 or 1, and start counting the next group, and what you call the group. A byte is a group of 8 bits. We group things for convenience. It’s a lot more inconvenient to carry 24 tins of beer home than a single box containing 24 tins
Sure, there are sectors, but, as far as I know, there are programmed at software level (at least in SSDs, I think)
Sectors and bytes are analogous in that they represent a grouping of something, but they aren’t necessarily directly related in the way that bits and bytes are because sectors are a level of grouping on top of bytes. Over time the meaning of a sector as a segment of a track (a reference to a platter number and a distance from the centre of the platter) has changed as the march of progress has done away with positional addressing and later even rotational storage. In computing you’ll typically find that there is a base level that is hard to use, so someone builds a level of abstraction on top of it, and that becomes the new “hard to use”, so it’s abstracted again, and again.
Also RAM, which is again - a long stream of ones and zeros
Yes, and is consequently hard to use, so it’s abstracted, and abstracted again. Your program doesn’t concern itself with raising the charge level of some capacitive area of a memory chip, it uses the abstractions it has access to, and that attraction fiddles the next level down, and so on until the magic happens at the bottom of the hierarchy. Where you stop on this downward journey is largely a question of definition and arbitrary choice. I don’t usually consider my ram chips as something like ice cube trays full of electrons, or the subatomic quanta, but I could I suppose. We normally stop when it ceases to useful to solving the Problem
Another example is CPU. It doesn't process 8 bits at a time, but only one.
That largely depends on your definition of ‘at a time’ - most of this question is about the definitions of various things. If we arbitrarily decide that ‘at a time’ is the unit block of the multiple picoseconds it takes the cpu to complete a single cycle then yes, a CPU can operate on multiple bits of information at once - it’s the whole idea of having a multiple bit cpu that can add two 32 bit numbers together and not forget bits. If you want to slice the time up so precisely that we can determine that enough charge has flowed to here but not there then you could say which bit the cpu is operating on right at this pico (or smaller) second, but it’s not useful to go so fine grained because nothing will happen until the end of the time slice the cpu is waiting for. Suffice to say, when we divide time just enough to observe a single cpu cycle from start to finish, we can say the cpu is operating on more than one bit.
If you write at one letter per second, and I close my eyes for 2 out of every 3 seconds, I’ll see you write a whole 3 letter word “at the same time” - you write “the cat sat onn the mat” and to the observer, you generated each word simultaneously. CPUs run cycles for similar reasons, they operate on the flow and buildup of electrical charge and you have to wait a certain amount of time for the charge to build up so that it triggers the next set of logical gates to open/close and direct the charge elsewhere. Faster CPUs are basically more sensitive circuitry; the rate of flow of charge is relatively constant, it’s the time you’re prepared to wait for input to flow from here to there, for that bucket to fill with just enough charge, that shortens with increasing MHz. Once enough charge has accumulated, bump! Something happens, and multiple things are processed “at the same time”
So where exactly is it specified? Or is it just general rule, which everyone follows?
it was the general rule, then it was specified to make sure it carried on being the general rule
If so, could I make system (either operating system or even something at lower level) that would use, let's say, 9 bits in a byte? Or I wouldn't have to?
You could, but you’d essentially have to write an adaptation(abstraction) of an existing processor architecture and you’d use nine 8bit bytes to achieve your presentation of eight 9bit bytes. You’re creating an abstraction on top of an abstraction and boundaries of basic building blocks don’t align. You’d have a lot of work to do to see the system out to completion, and you wouldn’t bother.
In the real world, if ice cube trays made 8 cubes at a time but you thought the optimal number for a person to have in the freezer was 9, you’d buy 9 trays, freeze them and make 72 cubes, then divvy them up into 8 bags, and sell them that way. If someone turned up with 9 cubes worth of water (it melted), you’d have to split it over 2 trays, freeze it, give it back.. this constant adaptation between your industry provided 8 slot trays and your desire to process 9 cubes is the adaptive abstraction
If you do do it, maybe call it a nyte? :)
Also - why can't you use less than a byte of memory? Or maybe you can?
You can, you just have to work with the limitations of the existing abstraction being 8 bits. If you have 8 Boolean values to store you can code things up so you flip bits of the byte on and off, so even though you’re stuck with your 8 cube ice tray you can selectively fill and empty each cube. If your program only ever needs 7 Booleans, you might have to accept the wastage of the other bit. Or maybe you’ll use it in combination with a regular 32 bit int to keep track of a 33bit integer value. Lot of work though, writing an adaptation that knows to progress onto the 33rd bit rather than just throw an overflow error when you try to add 1 to 4,294,967,295. Memory is plentiful enough that you’d waste the bit, and waste another 31bits using a 64bit integer to hold your 4,294,967,296 value.
Generally, resource is so plentiful these days that we don’t care to waste a few bits.. It isn’t always so, of course: take credit card terminals sending data over slow lines. Every bit counts for speed, so the ancient protocols for info interchange with the bank might well use different bits of the same byte to code up multiple things
For example: is it possible for two applications to use the same byte (e.g. first one uses 4 bits and second one uses other 4)?
No, because hardware and OS memory management these days keeps programs separate for security and stability. In the olden days though, one program could write to another program’s memory (it’s how we cheated at games, see the lives counter go down, just overwrite a new value), so in those days if two programs could behave, and one would only write to the 4 high bits and the other the 4 low bits then yes, they could have shared a byte. Access would probably be whole byte though, so each program would have to read the whole byte, only change its own bits of it, then write the entire result back
And last, but not least - does computer drives really use bytes? Or is it that, for example, bits 1-8 belong to something, next to them there are some 3 random bits and bits 12-20 belong to something different?
Probably not, but you’ll never know because you don’t get to peek to that level of abstraction enough to see the disk laid out as a sequence of bits and know where the byte boundaries are, or sector boundaries, and whether this logical sector follows that logical sector, or whether a defect in the disk surface means the sectors don’t follow on from each other. You don’t typically care though, because you treat the drive as a contiguous array of bytes (etc) and let its controller worry about where the bits are