Free Certification Practice Tests and Study Guides
Join Us! | Login | Help

A+ Study Guide: Domain 1.0: Personal Computer Components: Processors

:: Return to the Index ::

CPU Terms
Chip Characteristics
Bus Sizes of CPUs
Current Trends
Installing a Processor

The processor, also known as a microprocessor and the CPU, can be thought of as the brains of the system and is responsible for executing software commands and performing calculation functions. There are basically 2 CPU manufacturers today - Intel and AMD. Their processors are not interchangeable meaning that if you buy an AMD CPU, you must have a motherboard that supports AMD CPUs and vice versa.

A CPU's capabilities are defined by their "instruction set" which are lines of code that are passed back and forth over the external data bus. CPUs are rated by clock speed - this is the speed is the maximum speed that the CPU can operate at. The motherboard has a system crystal soldered to it that sends a pulse out at a given speed that is received by the CPU. This is referred to as the system bus speed. The CPU will normally operate at the system bus speed even if it can handle faster speeds. With most CPUs it is possible to tell the clock chip to operate to multiply the system pulse to go faster than the CPU's designed speed. This is called overclocking which is a risky option that can lead to hardware failure.

Now all processors are capable of operating at much faster speeds than the chips on the motherboard. To deal with this, CPU manufacturers began creating clock-multiplying CPUs which can operate at faster speeds for internal functions (they still communicate at slower speeds over the address bus and external data bus). The external speed, also known as the front side bus or FSB, is multiplied by the multiplier to give the internal CPU speed. For example, if the FSB has a clock speed of 133 MHz and the CPU multiplier is 10x, then the processor would run at 1.33 GHz.

The transistors on a motherboard use 5 volts of electricity, however, CPUs have varying voltages. Decreasing the voltage allows manufacturers to use smaller transistors, and hence, fit more of them into the CPU. To deal with the varying voltages, modern motherboards have an integrated Voltage Regulator Module (VRM) that adjusts the voltage level that the CPU receives from the system.

CPU Terms:
  • Registers - Registers are special storage locations located inside the CPU. The data contained here can be accessed much quicker than the data contained in other memory locations, such as the RAM (random-access memory) and the ROM (read-only memory). Registers in different parts of the CPU are used for different functions. In the control unit, the registers are used to store the computer's current instructions and the operands (this is merely a fancy term for data that is being operated on by the CPU). Meanwhile, the registers found in the ALU, called accumulators, are used to store the results of the arithmetic or logical operations.
  • Address Bus - The address bus is a collection of wires connecting the CPU with main memory that is used to identify particular locations (addresses) in main memory. The width of the address bus (that is, the number of wires) determines how many unique memory locations can be addressed.
  • Arithmetic/Logic Unit (ALU) - The ALU is the part of the CPU that does the actual computing and calculations sent to it by programs.
  • Cache
  • - Small memories on or close to the CPU chip can be made faster than the much larger main memory. Most CPUs since the 1980s have used one or more caches, and modern general-purpose CPUs inside personal computers may have as many as half a dozen, each specialized to a different part of the problem of executing programs. It is very similar to the concept of a browser cache that stores data from visited web sites making subsequent visits to those sites load faster.
  • Hyperthreading - The Intel Pentium 4 introduced hyperthreading which allows each pipeline to run more than one thread at a time. This essentially tricks the system into thinking that there are 2 processors. Hyperthreading only works with operating systems and applications that support it.
Chip Characteristics:
Note: You do not need to memorize the data in the following tables. It is here for reference purposes.

Processor Speed (MHz) Heat Sink Cooling Fan Cache Package Pins
8088 5-8 No No No DIP 40
80286 6
No No No LLC
80386SX 16 - 33 No No No PGA 100
80386DX 16 - 33 No No No PGA 100
80486SX 16 - 33 No Yes on 33 MHz 0-256K PGA 100
80486DX 25 - 50 No Yes on 33 MHz 0-256k PGA
Pentium 60-166 Yes Yes 256-512k PGA 296
Pentium Pro 233-266 Yes Yes 256k-1mb PGA 387
Pentium II 233-500 Yes Yes 512k SEC 242
Pentium III 450mhz-1.13ghz Yes Yes 256-512k SEC/PGA 242/370
Pentium IV 1.30-3.80ghz Yes Yes 256-512k PGA 423/478/775
Itanium 733-833mhz Yes Yes 96k PAC 418
Itanium II 900mhz-1.0ghz Yes Yes 256k OLGA 611
Pentium D 2.6GHz-3.6GHz Yes Yes 2x1mb-2x2mb OLGA 775
Intel Core 1.06GHz-2.33GHz Yes Yes 2mb Micro FCPGA 478
Intel Core 2 1.8GHz-3.2GHz Yes Yes 2mb or 4mb OLGA 775

  • With the Pentium MMX processors, 57 multimedia specific instructions were added to increase multimedia performance and increased the L1 cache size to 32KB.
  • The Pentium Pro added Dynamic Execution and increase L2 cache to 512KB.
  • The Pentium II had integrated MMX technology and used a new Single Edge Contact Cartridge(SEC).
  • The Pentium III provided increased processor speeds, a 100mhz front size bus speed and increased L2 cache to 512KB.
  • The Celeron processors are less expensive but only have a 66mhz bus and 128KB L2 cache.
  • The Pentium IV introduced a number of graphics enhancements. 2 versions were made - The first was a 423-pin PGA package with 256 KB L2 cache. The second version offers a 478-pin PGA package with 512 KB of L2 cache.
  • Intel Xeon processors are higher-end and based on their Pentium II, III and IV counterparts.
Bus Sizes of CPUs
Processor Register Data Bus Address Bus
8088 16-bit 8-bit 20-bit
80286 16-bit 16-bit 24-bit
80386SX 32-bit 16-bit 24-bit
80386DX 32-bit 32-bit 32-bit
80486SX 32-bit 32-bit 32-bit
80486DX 32-bit 32-bit 32-bit
Pentium 64-bit 64-bit 32-bit
Pentium Pro 64-bit 64-bit 36 bit
Pentium II 64-bit 64-bit 36 bit
Pentium III 64-bit 64-bit 36 bit
Pentium IV 64-bit 64-bit 36 bit
Itanium 64-bit 64-bit 44 bit
Itanium II 64-bit 128-bit 44 bit
Pentium D 64-bit ??? ???
Intel Core ??? ??? ???

While Intel holds the majority of the processor market share, companies such as AMD have been producing clones based on the X86 architecture. The table below outlines the various socket/slot types and the processors that they support.

Socket Pins Processor
Socket 4 237 PGA Pentium 60/66, Pentium Overdrive
Socket 5 320 PGA Pentium 75-133, Pentium Overdrive
Socket 7 321 PGA Pentium 75-200, Pentium Overdrive
Socket 8 387 PGA Pentium Pro
Slot 1 242 SEC/SEPP Pentium II, Pentium III, Celeron
Slot 2 330 SECC-2 Xeon
Super Socket 7 321 PGA Pentium MMX, Pentium Pro, AMD K6-2, K6-2+, K6-3, K6-3+
Socket 370 370 PGA Celeron, Pentium III, Cyrix III
Socket 418 418 PAC Itanium
Socket 423 423 PGA Pentium IV
Socket 478 478 PGA or microFCPGA Pentium IV, Intel Core, Intel Core 2
Socket 603 603 PGA Pentium IV-based Xeon, Xeon MP
Socket 611 611 OLGA Itanium II
Socket 754 754 Micro-PGA AMD Sempron, AMD Athlon 64
Socket 755 755 OLGA Pentium IV
Socket 775 775 OLGA Pentium D
Socket 939 Micro-PGA AMD Athlon 64, AMD Athlon 64 X2
Socket 940 Micro-PGA AMD Opteron, AMD Athlon 64
Socket A 462 PGA AMD Athlon, Athlon XP, Duron
Slot A 242 Slot A AMD Athlon

Current Trends:
A few years ago, Intel was the first to introduce a 64-bit processor (Itanium II). Since that time, 64 bit processors have become the standard. Clock speeds hit a brick wall at around 4GHz a few years back which forced CPU manufacturers to find new ways to squeeze more performance out of their chips. Intel and AMD both released "dual core" processors that are essentially 2 processors in one. The Intel Pentium D was basically 2 Pentium 4 processors together with their own cache. AMD launched a similar product called the AMD Athlon 64 X2 processor, however, the L1 cache was shared by the processors. Shortly after, Intel abandoned their Pentium line of processors which gave way to the Intel Core series. Core processors come in "Solo" or "Duo" (dual core) versions. This line was followed by the Intel Core 2 architecture that comes in "Duo" or "Extreme" versions.

Installing a Processor:
Before installing (or buying) a processor, you should make sure that your motherboard supports it. It is also very important to make sure that your motherboard uses the same package as your processor. In other words, a socket 775 processor (shown left) will not fit into a 478 socket. If you try to force it, you will likely bend the metal pins sticking out of the bottom of the processor. Typically, installation is as easy as placing the CPU in the socket and pushing down on the locking lever attached to the motherboard which can be seen on the left side of the image to the left. This lever is located on the side of the socket. Most CPUs and sockets are keyed so that you place it in the correct spot.

CPUs get very hot and the faster the CPU, the hotter it will get. This is why we need to attach a fan or newer cooling method such as a liquid cooling system. A typical cooling fan is pictured to the right. Before you install your fan, place a little bit of thermal compound on the top of the CPU. The fan will typically have clamps that lock onto the side of the socket on the motherboard. These can be difficult to install. Be patient and try not to damage your motherboard, especially when removing the fan. After securing the fan, you will need to plug in the power cable to the appropriate spot on your motherboard. See your motherboard manual for the location.

Further Reference:
CPU Tutorials
The Processor