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Two questions from univeristy professor that i have answered tomorrow?

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d@nny

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Three questions from univeristy professor that i have answered tomorrow?

1 = Why a byte is consist of 8 bit? No 7 bits not 5 bits or etc.
2 = i have a lot of time. time is ot a problem for me . so it is not problem that hard disk is slow . question is that why i cant change data firectly on the hard disk? Why it is need to load it in ram? Why data cant be modify directly on the hard disk?
3 = even you delete history temp files and cookie . But i can tell you what u do on computer even the key strokes and the click times? Where this file or log is in computer system?
 

Re: Three questions from univeristy professor that i have answered tomorrow?

1.The size of the byte has historically been hardware dependent and no definitive standards exist that mandate the size. The de facto standard of eight bits is a convenient power of two permitting the values 0 through 255 for one byte. Many types of applications use variables representable in eight or fewer bits, and processor designers optimize for this common usage. The popularity of major commercial computing architectures have aided in the ubiquitous acceptance of the 8-bit size.
Byte - Wikipedia, the free encyclopedia
2.Computer file - Wikipedia, the free encyclopedia

---------- Post added at 10:41 ---------- Previous post was at 10:40 ----------

1.The size of the byte has historically been hardware dependent and no definitive standards exist that mandate the size. The de facto standard of eight bits is a convenient power of two permitting the values 0 through 255 for one byte. Many types of applications use variables representable in eight or fewer bits, and processor designers optimize for this common usage. The popularity of major commercial computing architectures have aided in the ubiquitous acceptance of the 8-bit size.
Byte - Wikipedia, the free encyclopedia
2.Computer file - Wikipedia, the free encyclopedia

---------- Post added at 10:42 ---------- Previous post was at 10:41 ----------

3.**broken link removed**
 

Re: Three questions from univeristy professor that i have answered tomorrow?

1.The size of the byte has historically been hardware dependent and no definitive standards exist that mandate the size. The de facto standard of eight bits is a convenient power of two permitting the values 0 through 255 for one byte. Many types of applications use variables representable in eight or fewer bits, and processor designers optimize for this common usage. The popularity of major commercial computing architectures have aided in the ubiquitous acceptance of the 8-bit size.
Byte - Wikipedia, the free encyclopedia
2.Computer file - Wikipedia, the free encyclopedia

---------- Post added at 10:41 ---------- Previous post was at 10:40 ----------

1.The size of the byte has historically been hardware dependent and no definitive standards exist that mandate the size. The de facto standard of eight bits is a convenient power of two permitting the values 0 through 255 for one byte. Many types of applications use variables representable in eight or fewer bits, and processor designers optimize for this common usage. The popularity of major commercial computing architectures have aided in the ubiquitous acceptance of the 8-bit size.
Byte - Wikipedia, the free encyclopedia
2.Computer file - Wikipedia, the free encyclopedia

---------- Post added at 10:42 ---------- Previous post was at 10:41 ----------

3.**broken link removed**



You mean the question of my question no. 3 is index.dat file? Can you plz tells me the exact location of this file in windows computer?
I am still not able to get answer of my 2nd question why i cant modify a file on hard disk directly but not calling it in ram?
 

Why data cant be modify directly on the hard disk?
What does the question exactly mean? Modifying a single data bit, a data byte, a sector? Do you refer to the raw magnetic media or the disk drive unit (which incorporates RAM itself)?

For the magnetic media, a larger entity of data, a "sector" has to be rewritten to change a bit.
 

>>1 = Why a byte is consist of 8 bit? No 7 bits not 5 bits or etc.

It should be some number which is power of 2 (2^n). Initially the english alphabet was using 7 bit (ASCII 7 bit) so 8 bit is the closest 2^n digit to represent the characters.

>>2 = i have a lot of time. time is ot a problem for me . so it is not problem that hard disk is slow . question is that why i cant change data firectly on the hard disk? Why it is need to load it in ram? Why data cant be modify directly on the hard disk?

Even if you have a lot of time other people don't (and time is money). Theoretically there is no problem to read/write directly to the HDD but it's less efficient and slower. If you really insist to read and write directly to the HDD you can make it but nobody will be interested in your invention. Also as mentioned FvM the data on the disk is organized in records and each record has CRC so simply changing a single byte on the disk will result is CRC error on this record - you need to rewrite the whole record at once.

>>3 = even you delete history temp files and cookie . But i can tell you what u do on computer even the key strokes and the click times? Where this file or log is in computer system?
That's not true - normally the computer has no log data for the keyboard presses. Of course there are existing a lot of "keyboard sniffers" which record any activity of the keyboard. That means - if you want to spy some computer you need to use some special program or hardware to record the keyboard strokes, computers don't have "build in" feature to do this.
 
can i modify a ms word file directly on the hard disk with out loading it in hard disk? If not than why?
 

Although you didn't tell, what modify on the hard disk exactly means, I'm under the impression that it has been already explained, why it's not possible.
 

you mean it is possible to modify any data on the hard disk with out loading it in the ram directly?
How?
 

No, you can only write data blocks (full sectors) to a harddisk. Changing e.g. single bytes involves read, modfy, write.
 
Hi FvM,

If we speak about existing HDD with the sector organization it's impossible to write single bit- or if it's possible you need to access deeply the firmware of the HDD and to violate the existing HDD data structure. But if we speak theoretically - it's possible. The first hard disks which were the size of washing mashine with capacity of 64 Kb allowed in some circumstances the record of a single bit- the position of the bit on the track was just delay from the sector index so it was possible simply to access the desired bit. Until the new generation engineers never had seen such old style hard drives we could conclude that writing single bit in existing HDD is not possible without reading the sector into ram, changing the bit and writing back onto disk the data.
 

But if we speak theoretically - it's possible.

Your comment refers to the ambiguity of the question. A HDD with respective firmware could do - utilizing it's internal RAM. On the magnetic media itself it's not possible, because you can't write a partial sector without creating discontinuities. I must confess, that I don't know what's the actual entity written on a recent HDD drive, it may be even a full track. The floppy disks we have been dealing with in older days are written in sectors and formatted a whole track at once.
 

I think the processor can directly read the data from the hard disk , modify the data and again write it to the hard directly with out the involving of the ram with the help of direct memory access? Am i right?

---------- Post added at 11:09 ---------- Previous post was at 11:08 ----------

**broken link removed**
 

DMA is between RAM and peripheral (hard disk) in this case. It doesn't change anything to the problem.
 

DMA is between RAM and peripheral (hard disk) in this case. It doesn't change anything to the problem.
i cant understand you mean DMA or direct memory access is a link between RAM and hard disk?
But i think it is link between processor and memory devices like hard disk . And with the help of the DMA the processor can directly modify data on the hard disk with out involving ram?
 

The term DMA already indicates, that memory (RAM) is involved in the data transfer. The typical DMA situation is transferring data between RAM and hard disk without direct involvement of the CPU.
 

Consider FAT systems(Fat16,Fat32,eXfat,ntfc etc) used for data storage and its requirments also. Or try to write raw data bit by bit in your own file system.
 

The term DMA already indicates, that memory (RAM) is involved in the data transfer. The typical DMA situation is transferring data between RAM and hard disk without direct involvement of the CPU.
Ohh!
thats mean i couldn't understand the DMA article on wikipedia? and i write wrong in my blog. please read once the above html link . In clear words DMA or direct memory access is the technology of loading data into the ram from cd rom / dvd rom or hard disk or sending data to these devices from ram without the involving of the cpu?
DMA is not the technology of loading data from the harddisk or CD rom into the cpu with out involving ram?

Please clear it in easy words and once read my post in this link. **broken link removed**
 

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