Chapter 3. CPUs
EXAM TIP – answer CompTIA only uses the term CPU, not microprocessor. Expect to
see CPU on the 1001 exam.
general-purpose registers – answer CPUs contain a large number of registers, but for
the moment let's concentrate on the four most common ones: the general-purpose
registers. Intel named them AX, BX, CX, and DX.
clock - answer The CPU does nothing until activated by the clock
Each time you press the button to sound the bell, the Man in the Box reads the next set
of lights on the EDB. Of course, a real computer doesn't use a bell. The bell on a real
CPU is a special wire called the clock wire (most diagrams label the clock wire CLK).
A charge on the CLK wire tells the CPU that another piece of information is waiting to
be processed
- answer For the CPU to process a command placed on the EDB, a certain minimum
voltage must be applied to the CLK wire.
A single charge to the CLK wire is called a clock cycle.
Actually, the CPU requires at least two clock cycles to act on a command, and usually
more. In fact, a CPU may require hundreds of clock cycles to process some commands
clock speed - answerthe maximum number of clock cycles that a CPU can handle in a
given period of time is referred to as its clock speed. The clock speed is the fastest
speed at which a CPU can operate, determined by the CPU manufacturer. The Intel
8088 processor had a clock speed of 4.77 MHz (4.77 million cycles per second),
extremely slow by modern standards, but still a pretty big number compared to using a
pencil and paper. High-end CPUs today run at speeds in excess of 5 GHz (5 billion
cycles per second). You'll see these "hertz" terms a lot in this chapter, so here's what
they mean:
Hz (Hertz) - answer1 hertz (1 Hz) = 1 cycle per second
1 megahertz (1 MHz) = 1 million cycles per second
1 gigahertz (1 GHz) = 1 billion cycles per second
system crystal - answerThe system crystal determines the speed at which a CPU and
the rest of the PC operate. The system crystal is usually a quartz oscillator, very similar
to the one in a wristwatch, soldered to the motherboard
,clock speed - answerVisualize the system crystal as a metronome for the CPU.
The quartz oscillator repeatedly fires a charge on the CLK wire, setting the beat, if you
will, for the CPU's activities. If the system crystal sets a beat slower than the CPU's
clock speed, the CPU will work just fine, though at the slower speed of the system
crystal. If the system crystal forces the CPU to run faster than its clock speed, it can
overheat and stop working.
External Data bus, and Clock on actual chip - answer
MEMORY - answerDevices that in any way hold ones and zeros that the CPU accesses
are known generically as memory
random access memory (RAM). - answerAny individual 1 or 0 = a bit
4 bits = a nibble
8 bits = a byte
16 bits = a word
32 bits = a double word
64 bits = a paragraph or quad word
Random Access - answerThe CPU accesses any one row of RAM as easily and as fast
as any other row, which explains the "random access" part of RAM.
Not only is RAM randomly accessible, it's also fast. By storing programs on RAM, the
CPU can access and run them very quickly. RAM also stores any data that the CPU
actively uses.
Computers use dynamic RAM (DRAM) for the main system memory. -
answerComputers use dynamic RAM (DRAM) for the main system memory.
DRAM needs both a constant electrical charge and a periodic refresh of the circuits;
otherwise, it loses data—that's what makes it dynamic rather than static in content.
DRAM - answerBecause of its low cost, high speed, and capability to contain a lot of
data in a relatively small package, DRAM has been the standard RAM used in all
computers—not just PCs—since the mid-1970s.
DRAM can be found in just about everything, from automobiles to automatic bread
makers.
8 bits = 1 byte - answer
EXTERNAL DATA BUS - answerEXTERNAL DATA BUS
So far, the entire PC consists of only a CPU and RAM. But the CPU and the RAM need
some connection so they can talk to each other. To do so, extend the external data bus
from the CPU so it can talk to the RAM
, Figure 3-16: Extending the EDB(see Figure 3-16).
MCC :memory controller chip (MCC). - answermemory controller chip (MCC)
We need some type of chip between the RAM and the CPU to make the connection.
The CPU needs to be able to say which row of RAM it wants, and the chip should
handle the mechanics of retrieving that row of data from the RAM and putting it on the
EDB.
This chip comes with many names, but for right now just call it the memory controller
chip (MCC).
The MCC contains special circuitry so it can grab the contents of any line of RAM and
place that data or command on the EDB. This in turn enables the CPU to act on that
code
Figure 3-17: The MCC grabs a byte of RAM
ADDRESS BUS - answerOnce the MCC is in place to grab any discrete byte of RAM,
the CPU needs to be able to tell the MCC which line of code it needs.
The CPU therefore gains a second set of wires, called the address bus, with which it
can communicate with the MCC.
Different CPUs have different numbers of wires (which, you will soon see, is very
significant). The 8088 had 20 wires in its address bus
address space - answerTotal amount of memory addresses that an address bus can
contain.
Because the 8088 had a 20-wire address bus, the most RAM it could handle was 220 or
1,048,576 bytes. The 8088, therefore, had an address space of 1,048,576 bytes.
Okay, so you know that the 8088 had 20 address wires and a total address space of
1,048,576 bytes.
no one called it that, instead: Instead you say that the 8088 had one megabyte (1 MB)
of address space.
- answer1 kilo = 2^10 = 1024 (as K)
1 kilobyte = 1024 bytes (as "KB")
1 mega = 2^20 = 1,048,576 (as "M")
1 megabyte = 1,048,576 bytes (as "MB")
EXAM TIP – answer CompTIA only uses the term CPU, not microprocessor. Expect to
see CPU on the 1001 exam.
general-purpose registers – answer CPUs contain a large number of registers, but for
the moment let's concentrate on the four most common ones: the general-purpose
registers. Intel named them AX, BX, CX, and DX.
clock - answer The CPU does nothing until activated by the clock
Each time you press the button to sound the bell, the Man in the Box reads the next set
of lights on the EDB. Of course, a real computer doesn't use a bell. The bell on a real
CPU is a special wire called the clock wire (most diagrams label the clock wire CLK).
A charge on the CLK wire tells the CPU that another piece of information is waiting to
be processed
- answer For the CPU to process a command placed on the EDB, a certain minimum
voltage must be applied to the CLK wire.
A single charge to the CLK wire is called a clock cycle.
Actually, the CPU requires at least two clock cycles to act on a command, and usually
more. In fact, a CPU may require hundreds of clock cycles to process some commands
clock speed - answerthe maximum number of clock cycles that a CPU can handle in a
given period of time is referred to as its clock speed. The clock speed is the fastest
speed at which a CPU can operate, determined by the CPU manufacturer. The Intel
8088 processor had a clock speed of 4.77 MHz (4.77 million cycles per second),
extremely slow by modern standards, but still a pretty big number compared to using a
pencil and paper. High-end CPUs today run at speeds in excess of 5 GHz (5 billion
cycles per second). You'll see these "hertz" terms a lot in this chapter, so here's what
they mean:
Hz (Hertz) - answer1 hertz (1 Hz) = 1 cycle per second
1 megahertz (1 MHz) = 1 million cycles per second
1 gigahertz (1 GHz) = 1 billion cycles per second
system crystal - answerThe system crystal determines the speed at which a CPU and
the rest of the PC operate. The system crystal is usually a quartz oscillator, very similar
to the one in a wristwatch, soldered to the motherboard
,clock speed - answerVisualize the system crystal as a metronome for the CPU.
The quartz oscillator repeatedly fires a charge on the CLK wire, setting the beat, if you
will, for the CPU's activities. If the system crystal sets a beat slower than the CPU's
clock speed, the CPU will work just fine, though at the slower speed of the system
crystal. If the system crystal forces the CPU to run faster than its clock speed, it can
overheat and stop working.
External Data bus, and Clock on actual chip - answer
MEMORY - answerDevices that in any way hold ones and zeros that the CPU accesses
are known generically as memory
random access memory (RAM). - answerAny individual 1 or 0 = a bit
4 bits = a nibble
8 bits = a byte
16 bits = a word
32 bits = a double word
64 bits = a paragraph or quad word
Random Access - answerThe CPU accesses any one row of RAM as easily and as fast
as any other row, which explains the "random access" part of RAM.
Not only is RAM randomly accessible, it's also fast. By storing programs on RAM, the
CPU can access and run them very quickly. RAM also stores any data that the CPU
actively uses.
Computers use dynamic RAM (DRAM) for the main system memory. -
answerComputers use dynamic RAM (DRAM) for the main system memory.
DRAM needs both a constant electrical charge and a periodic refresh of the circuits;
otherwise, it loses data—that's what makes it dynamic rather than static in content.
DRAM - answerBecause of its low cost, high speed, and capability to contain a lot of
data in a relatively small package, DRAM has been the standard RAM used in all
computers—not just PCs—since the mid-1970s.
DRAM can be found in just about everything, from automobiles to automatic bread
makers.
8 bits = 1 byte - answer
EXTERNAL DATA BUS - answerEXTERNAL DATA BUS
So far, the entire PC consists of only a CPU and RAM. But the CPU and the RAM need
some connection so they can talk to each other. To do so, extend the external data bus
from the CPU so it can talk to the RAM
, Figure 3-16: Extending the EDB(see Figure 3-16).
MCC :memory controller chip (MCC). - answermemory controller chip (MCC)
We need some type of chip between the RAM and the CPU to make the connection.
The CPU needs to be able to say which row of RAM it wants, and the chip should
handle the mechanics of retrieving that row of data from the RAM and putting it on the
EDB.
This chip comes with many names, but for right now just call it the memory controller
chip (MCC).
The MCC contains special circuitry so it can grab the contents of any line of RAM and
place that data or command on the EDB. This in turn enables the CPU to act on that
code
Figure 3-17: The MCC grabs a byte of RAM
ADDRESS BUS - answerOnce the MCC is in place to grab any discrete byte of RAM,
the CPU needs to be able to tell the MCC which line of code it needs.
The CPU therefore gains a second set of wires, called the address bus, with which it
can communicate with the MCC.
Different CPUs have different numbers of wires (which, you will soon see, is very
significant). The 8088 had 20 wires in its address bus
address space - answerTotal amount of memory addresses that an address bus can
contain.
Because the 8088 had a 20-wire address bus, the most RAM it could handle was 220 or
1,048,576 bytes. The 8088, therefore, had an address space of 1,048,576 bytes.
Okay, so you know that the 8088 had 20 address wires and a total address space of
1,048,576 bytes.
no one called it that, instead: Instead you say that the 8088 had one megabyte (1 MB)
of address space.
- answer1 kilo = 2^10 = 1024 (as K)
1 kilobyte = 1024 bytes (as "KB")
1 mega = 2^20 = 1,048,576 (as "M")
1 megabyte = 1,048,576 bytes (as "MB")
