#8088 5mhz memory speed ns full

Indeed, on many 80x86 processors, it takes several clock cycles to access a memory location. That is, reading a value from memory or writing a value to memory occurs no more often than once every clock cycle. Memory access is definitely an operation synchronized around the system clock. Memory access is probably the most common CPU activity. Many operations take multiple clock cycles to complete so the CPU often performs operations at a significantly lower rate. However, just because a CPU is running at some clock frequency doesn't mean that it is executing that many operations each second. Since all CPU operations are synchronized around the clock, the CPU cannot perform tasks any faster than the clock. Therefore clock edge is the perfect synchronization point. The system clock spends most of its time at either zero or one and very little time switching between the two. To ensure synchronization, most CPUs start an operation on either the falling edge (when the clock goes from one to zero) or the rising edge (when the clock goes from zero to one). Note that we usually express clock periods in millionths or billionths of a second. A CPU running at 50 MHz would have a clock period of 20 nanoseconds.

Likewise, a 10 MHz clock would have a clock period of 100 nanoseconds (100 billionths of a second). For example, a 1 MHz clock would have a clock period of one microsecond (1/1,000,000 th of a second). Note that one clock period (the amount of time for one complete clock cycle) is the reciprocal of the clock frequency. Typical frequencies for 80x86 parts range from 5 MHz up to 200 MHz and beyond. Therefore, the aforementioned 80486 chip runs at 66 million hertz, or 66 megahertz (MHz). 'Hertz' (Hz) is the technical term meaning one cycle per second. A typical 80486 chip runs at speeds of 66million cycles per second. The clock frequency is simply the number of clock cycles which occur each second. On most modern systems, the system clock switches between zero and one at rates exceeding several million times per second.

#8088 5mhz memory speed ns full

One full period is also called a clock cycle. The time it takes for the system clock to switch from zero to one and back to zero is the clock period. The frequency with which the system clock alternates between zero and one is the system clock frequency. The system clock gates many of the logic gates that make up the CPU allowing them to operate in a synchronized fashion. The system clock is an electrical signal on the control bus which alternates between zero and one at a periodic rate:ĬPUs are a good example of a complex synchronous logic system (see the previous chapter). To ensure that all operations occur at just the right moment, the 80x86 CPUs use an alternating signal called the system clock.Īt the most basic level, the system clock handles all synchronization within a computer system.

Without going into too many details, let us just say that operations inside the CPU must be very carefully coordinated or the CPU will produce erroneous results. The CPU is a very complex piece of circuitry. For those interested in writing fast software, a natural question to ask is, 'How does the processor execute statements, and how do we measure how long they take to execute?' As you might expect, the second Pascal statement above takes quite a bit longer to execute than the first. Likewise, multiplying I by five and then adding two and storing the result back into I takes time. Moving a copy of J into I takes a certain amount of time. Of course, on real computer systems, operations do not occur instantaneously. It wouldn't do, for example, to execute the statement I:=I*5+2 before I :=J in the following sequence:Ĭlearly we need some way to control which statement executes first and which executes second. This means that the computer executes commands in a prescribed order. On Von Neumann machines, like the 80x86, most operations are serialized. Art of Assembly: Chapter Three-2 ģ.2 - System Timing 3.2.1 - The System Clock 3.2.2 - Memory Access and the System Clock 3.2.3 - Wait States 3.2.4 - Cache MemoryĪlthough modern computers are quite fast and getting faster all the time, they still require a finite amount of time to accomplish even the smallest tasks.