Monday, June 30, 2008
Gates
The manipulation of binary information is done by logic circuits called gates. Gates are blocks of hardware that produce signals of binary 1 or 0 when input logic requirements are satisfied. A variety of logic gates are commonly used in digital computer systems. Each gate has a distinct graphic symbol and its operation can be described by means of an algebraic expression. The input-output relationship of the binary variables for each gate can be represented in tabular form by a truth table.
Saturday, June 28, 2008
SHIFT REGISTER
A register that is capable of shifting data one bit at a time is called a shift register. The logical configuration of a serial shift register consists of a chain of flip-flops connected in cascade, with the output of one flip-flop being connected to the input of its neighbour. The operation of the shift register is synchronous; thus each flip-flop is connected to a common clock. Using D flip-flops forms the simplest type of shift-registers.
For more details abt this are in these following sites...scitec.uwichill.edu.bb/cmp/online/P10F/shift.htm
www.doctronics.co.uk/4014.htm
Difference between LAN and WAN
LAN versus WAN
To define a LAN
Up to now we've been talking about Ethernet and I've made reference to the fact that Ethernet is a LAN.
A LAN is a Local Area Network. Local is generally referred to a network contained within a building or an office or a campus.
Examples:
You might have a LAN for example on a University campus or between office blocks in an office park.
A big corporate perhaps like Anglo American, would generally have a LAN that might span several buildings.
To set up a LAN -relatively speaking- is cheap. If you want to put an extra couple of network points or an extra couple of devices on the network, it 's not very expensive to do that.
To define a WAN
Using a similar example, a Wide Area Network is a network that connects campuses.
What I'm going to do is write down some short descriptions of what a WAN is:
1. A WAN is generally slow. If we compare that to a LAN, we said that Ethernet could run up to 1000 Mbs, currently, certainly in South Africa, the fastest WAN is 155 Mbs, so you can see in a LAN we can talk up to 1000 Mbs whereas in a WAN, at the moment, currently, today in South Africa, we can only take, literally a 10th of the speed.
2. WAN's are expensive. If we look at the path of telecommunications, we need to connect two offices, one in Pretoria and one in Johannesburg together - it 's an expensive operation even for a slow line.
One of the differences between a WAN (Wide Area Network) and a LAN (Local Area Network) is the set-up cost. WAN generally are to connect remote offices and when we talk about remote offices we generally refer to the remote offices as those that are outside the campus. For example, if we have an office in Pretoria and we have an office in Cape Town, these are remote offices. There is no chance that we can connect the LAN between Cape Town and Pretoria. In a LAN we connect local offices whereas in a WAN we can connect remote offices.
To define a LAN
Up to now we've been talking about Ethernet and I've made reference to the fact that Ethernet is a LAN.
A LAN is a Local Area Network. Local is generally referred to a network contained within a building or an office or a campus.
Examples:
You might have a LAN for example on a University campus or between office blocks in an office park.
A big corporate perhaps like Anglo American, would generally have a LAN that might span several buildings.
To set up a LAN -relatively speaking- is cheap. If you want to put an extra couple of network points or an extra couple of devices on the network, it 's not very expensive to do that.
To define a WAN
Using a similar example, a Wide Area Network is a network that connects campuses.
What I'm going to do is write down some short descriptions of what a WAN is:
1. A WAN is generally slow. If we compare that to a LAN, we said that Ethernet could run up to 1000 Mbs, currently, certainly in South Africa, the fastest WAN is 155 Mbs, so you can see in a LAN we can talk up to 1000 Mbs whereas in a WAN, at the moment, currently, today in South Africa, we can only take, literally a 10th of the speed.
2. WAN's are expensive. If we look at the path of telecommunications, we need to connect two offices, one in Pretoria and one in Johannesburg together - it 's an expensive operation even for a slow line.
One of the differences between a WAN (Wide Area Network) and a LAN (Local Area Network) is the set-up cost. WAN generally are to connect remote offices and when we talk about remote offices we generally refer to the remote offices as those that are outside the campus. For example, if we have an office in Pretoria and we have an office in Cape Town, these are remote offices. There is no chance that we can connect the LAN between Cape Town and Pretoria. In a LAN we connect local offices whereas in a WAN we can connect remote offices.
DIFFERENCE BETWEEN ARITHMETIC AND LOGICAL SHIFT
All shifts can be categorized as logical, arithmetic, or circular. In a logical shift, a zero enters at the input of the shifter and the bit shifted out is clocked into the carry flip-flop of the CCR. An arithmetic shift left is identical to a logical shift left, but an arithmetic shift right causes the most significant bit, the sign bit, to be propagated right. This action preserves the correct sign of a two's complement value. For example, if the bytes 00101010 and 10101010 are shifted one place right (arithmetically), the results are 00010101 and 11010101, respectively.
PROGRAM COUNTER
program counter
PC, or "instruction address register"...
A register in the central processing unit that contains the addresss of the next instruction to be executed. The PC is automatically incremented after each instruction is fetched to point to the following instruction. It is not normally manipulated like an ordinary register but instead, special instructions are provided to alter the flow of control by writing a new value to the PC, e.g. JUMP, CALL
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