[H4R0015K]

I Was thinking what would be the memory size of casio fx-991MS calculator...at a time i can only type 72 numbers..does it means its memory size is of 9Byte??

[Frooxius]

I highly doubt it's 9 bytes, I don't even know how you got the 9 bytes, or what do you mean by 72 numbers. Don't you mean 72 digits?

It depends on how these numbers are actually stored, but generally storage only for the digits themselves would not be enough, as the calculator needs additional memory for various operations and/or storing intermediate results or even the current cursor position, previous results and such. It seems to have special functions and it evaluates simple math expressions, so it needs enough memory for parsing and storing the structure of these and evaluating them.

Some calculations aren't done at once, but instead it can use iterations to get the final result, having to store additional variables for the iterations. Simply, there's more than meets the eye, it needs more memory for its internal operations and tasks.

It can have multiple memories, one volatile (operating memory - RAM) for fast access and some non-volatile, but slower for permanent storage. However some devices have only RAM, so when you remove the battery, all the settings and stored data are erased, which is usually not an issue with this kind of device and is simpler and cheaper.

However it's impossible to say how much memory it actually has, because it all depends on how is the hardware designed, I tried looking up specifications, but I can't find any at this moment. There are many ways to achieve various functions, some are more memory intensive and some are less, it's also important to know how much data it needs to store at any time at once and it might actually have specifically designed circuits for some operations, which have some internal registers to store the intermediate values...

If I had to take a wild guess, I think it uses some MCU (micro-controller, it's a type of processor, different from CPU. It's low power, low performance (but that's okay for a calculator) processor with many integrated peripherals, including a small amount of RAM and ROM memory which holds the program. It depends on the model of MCU though, but if you manage to find out that, we can look it up in datasheets and find out how much memory it actually has, unless they extended the MCU with additional circuitry for some operations, although I doubt that.

[H4R0015K]

I highly doubt it's 9 bytes, I don't even know how you got the 9 bytes, or what do you mean by 72 numbers. Don't you mean 72 digits?

It depends on how these numbers are actually stored, but generally storage only for the digits themselves would not be enough, as the calculator needs additional memory for various operations and/or storing intermediate results or even the current cursor position, previous results and such. It seems to have special functions and it evaluates simple math expressions, so it needs enough memory for parsing and storing the structure of these and evaluating them.

Some calculations aren't done at once, but instead it can use iterations to get the final result, having to store additional variables for the iterations. Simply, there's more than meets the eye, it needs more memory for its internal operations and tasks.

It can have multiple memories, one volatile (operating memory - RAM) for fast access and some non-volatile, but slower for permanent storage. However some devices have only RAM, so when you remove the battery, all the settings and stored data are erased, which is usually not an issue with this kind of device and is simpler and cheaper.

However it's impossible to say how much memory it actually has, because it all depends on how is the hardware designed, I tried looking up specifications, but I can't find any at this moment. There are many ways to achieve various functions, some are more memory intensive and some are less, it's also important to know how much data it needs to store at any time at once and it might actually have specifically designed circuits for some operations, which have some internal registers to store the intermediate values...

If I had to take a wild guess, I think it uses some MCU (micro-controller, it's a type of processor, different from CPU. It's low power, low performance (but that's okay for a calculator) processor with many integrated peripherals, including a small amount of RAM and ROM memory which holds the program. It depends on the model of MCU though, but if you manage to find out that, we can look it up in datasheets and find out how much memory it actually has, unless they extended the MCU with additional circuitry for some operations, although I doubt that.

thanks for your time...by 72 numbers i mean 72 digits..i got 9byte by considering 72 digits as bits .. i will try to find its MCU

[Frooxius]

If you were to store a number as an integer using 9 bytes, you could store any integer number between:
+2361183241434822606847 and -2361183241434822606848

However it almost certainly doesn't use such format, it doesn't even allow you to work with fractional numbers. Instead, it can use some floating point type and if you type a number that's too large, it will convert it to floating point type (it usually uses 32 or 64 bits to store a number, that's 4 or 8 bytes, it has very large range, but limited precision) and it will truncate the value to whatever nearest number can be expressed with the datatype, meaning all the extra digits you typed will be lost, it works exactly the same with regular computers.

However, when you're typing the number on the display, it might actually store each digit individually (instead of storing it as a whole number) in the memory, basically storing it as character or some kind of "token", as you can mix it with the operation symbols, parentheses and such, so it would probably use 1 byte for every symbol (although symbols like "sin" and "cos" would be probably stored as one, so 1 byte for them as well), so you would need at least 72 bytes to store the current expression.

The processor itself has limitations in what operations to what precision it can perform natively (and quickly), I guess the calculator has some FPU unit and either does everything using floating point operations, or uses integer and floating point arithmetic based on which one is better for given task. However both integer and floating datatypes can store only certain numbers, so they're limited in range and precision, because you need to fit the number into finite space.

The precision and range is usually good enough for most uses, although if you want to do some scientific calculations and such and you need very high precision, you might look into arbitrary precision math libraries and more advanced calculators that support that, in which case the memory requirements to store the numbers change dynamically.

[H4R0015K]

man you are a true guru...stay tuned lots of question are coming for you..