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16F877 microcontroller memory size is 8k(8192 X 14 bits)
8192 derived from , 1k = 1024 byte
so, 8k= 1024 X 8 = 8192 its clear for me..
but what is 14 bits and why is multiplied with 8192 please explain...
The 16F877 has 14 bit wide instructions. Therefore 8192 X 14 bits refers to having 8192 instructions each of which take up 14 bits.
Microchip is counting the flash memory of the PIC16 family in words (one word is 14 Bit wide).
But they are counting the memory of the PIC18, PIC24 and PIC 32 family in Bytes. So you had to pay attention if you want to compare the memory of the different families.
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While developing a brute force based cracking algorithm for unix password I met with this line: "salt is a two-character string chosen from the set [a-zA-Z0-9./]. This string is used to perturb the algorithm in one of 4096 different ways."
I did not get 4096 ways?? 2^12 but how??
The set [a-zA-Z0-9./] is made up of 64 characters. Selecting two characters each from the full 64 character set gives 64 * 64 possibilities, or 4096.
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I have a random number sequence (say 6 bytes)
I now want to generate a shorter sequence from the original sequence (say 3 bytes)
What is the best way of acheiving this so that the randomness of the original sequence is preserved.
Lets say I run a SHA-1 hash code on the original sequence and then grab some bytes from the hashed output. Does the randomness decrease, increase, or stay the same.
The basic question is - Does a Hash Code of a random number produce less random, more random or same randomness.
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Im using a genetic algorithm (witness.genetic from package "witness") to fit a model to a dataset. The current system time is taking 61 hours on this machine:
Intel Core i7-2640M CPU # 2.80 GHz 2.80 GHz
RAM: 4 GB
OS: 64-bit windows
I want to speed up this process. In my research so far its seems there are memory issues both with storage of a vector (for a 64-bit ) and processing speed. Will improving my hardware help with speed up a genetic algorithm or the speed limited by the OS. IF the former, what aspects of my hardware should I focus on?
The answer is almost always to write a better algorithm! Moore's law says upgrading a 10 year old computer will give a 32 times speed-up. But designing a O(n log n) algorithm to replace a O(n**2) algorithm will give a 2500 speed up (assuming there are 10k items).
Read Steven Skiena's Algorithm Design Manual for examples.
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I have been learning subnetting for my exam and I came through this question.
but why it this? I first thought: 172.20.0.0 can have 254 subnets and 254 Hosts per each subnet. I obviously was wrong. can you please explain me how to get this?
thanks guys
The netmask 255.255.252.0 has 10 zero bits at the end.
2 ^ 10 = 1024, minus a broadcast and a network address = 1022.
If you're using the classful way of dividing your network, 172.20.* is a B network, with a 16 bit size of the network part. That gives 16-10 = 6 bits to spare, that can be split into 2 ^ 6 = 64 networks.
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I'm setting up an old wireless router for a friend which uses WEP (Yeah, very old, not actually very secure, but enough to keep the non-technical people in her apartment complex from sucking bandwidth) and I need to have a 10 digit hexadecimal key as the password.
So the question is, what english words can be made using the hexadecimal character set:
1 2 3 4 5 6 7 8 9 0 A B C D E F
BEEF is an example. I think that leet character would be allowed as well, So the number 0 could be used for the letter o. This lets you make the word BEA7.
Java CAFEBABE, COFEEBABE or DEADBEEF for instance. You might like to check HexWords or Ned Batchelder Hex Words for a lot more examples.