Microprocessor
A microprocessor is a programmable digital electronic component that incorporates the functions of a central processing unit (CPU) on a single semiconducting integrated circuit (IC). The microprocessor was born by reducing the word size of the CPU from 32 bits to 4 bits, so that the transistors of its logic circuits would fit onto a single part. One or more microprocessors typically serve as the CPU in a computer system, embedded system, or handheld device. A device that integrates the functions of the central processing unit (CPU) of a computer onto one semiconductor chip or integrated circuit (IC). In essence, the microprocessor contains the core elements of a computer system, its computation and control engine. Only a power supply, memory, peripheral interface ICs, and peripherals (typically input/output and storage devices) need be added to build a complete computer system.

CISC Chips
Pronounced sisk, and stands for Complex Instruction Set Computer. Most PC's use CPU based on this architecture. For instance Intel and AMD CPU's are based on CISC architectures. Typically CISC chips have a large amount of different and complex instructions. The philosophy behind it is that hardware is always faster than software, therefore one should make a powerful instructionset, which provides programmers with assembly instructions to do a lot with short programs. In common CISC chips are relatively slow (compared to RISC chips) per instruction, but use little (less than RISC) instructions. A complex instruction set computer (CISC) is a microprocessor instruction set architecture (ISA) in which each instruction can execute several low-level operations, such as a load from memory, an arithmetic operation, and a memory store, all in a single instruction. The term was retroactively coined in contrast to reduced instruction set computer (RISC).

CISC
Emphasis on hardware
Includes multi-clockcomplex instructions
Memory-to-memory:"LOAD" and "STORE"incorporated in instructions
Small code sizes,high cycles per second
Transistors used for storingcomplex instructions

RISC Chips
Pronounced risk, and stands for Reduced Instruction Set Computer. RISC chips evolved around the mid-1980 as a reaction at CISC chips. The philosophy behind it is that almost no one uses complex assembly language instructions as used by CISC, and people mostly use compilers which never use complex instructions. Apple for instance uses RISC chips. Therefore fewer, simpler and faster instructions would be better, than the large, complex and slower CISC instructions. However, more instructions are needed to accomplish a task. An other advantage of RISC is that - in theory - because of the more simple instructions, RISC chips require fewer transistors, which makes them easier to design and cheaper to produce. The reduced instruction set computer, or RISC, is a CPU design philosophy that favors an instruction set reduced both in size and complexity of addressing modes, in order to enable easier implementation, greater instruction level parallelism, and more efficient compilers. As of 2007, common RISC microprocessors families include the DEC Alpha, ARC, ARM, AVR, MIPS, PA-RISC, Power Architecture (including PowerPC), and SPARC.

RISC
Emphasis on software
Single-clock,reduced instruction only
Register to register:"LOAD" and "STORE"are independent instructions
Low cycles per second,large code sizes
Spends more transistorson memory registers

Memory Chips
A chip that holds programs and data either temporarily (RAM), permanently (ROM, PROM) or permanently until changed (EPROM, EEPROM, flash memory).

Kinds of Memory Chips
*SIMMS

The term SIMM stands for Single In-Line Memory Module. With SIMMs, memory chips are soldered onto a modular printed circuit board (PCB), which inserts into a socket on the system board. The first SIMMs transferred 8 bits of data at a time. Later, as CPUs began to read data in 32-bit chunks, a wider SIMM was developed, which could supply 32 bits of data at a time. The easiest way to differentiate between these two different kinds of SIMMs was by the number of pins, or connectors. The earlier modules had 30 pins and the later modules had 72 pins. Thus, they became commonly referred to as 30-pin SIMMs and 72-pin SIMMs.

*DIMMS

Dual In-line Memory Modules, or DIMMs, closely resemble SIMMs. Like SIMMs, most DIMMs install vertically into expansion sockets. The principal difference between the two is that on a SIMM, pins on opposite sides of the board are "tied together" to form one electrical contact; on a DIMM, opposing pins remain electrically isolated to form two separate contacts. DIMMs come in various form factors and are specific to different DRAM technologies. 168-pin DIMM: EDO and PC66/100/133 SDRAM 184-pin DIMM: DDR 200/266/333/400 DDR SDRAM 240-pin DIMM: DDR2 400/533/667/800 DDR-2 SDRAM DIMMs transfer 64 bits of data at a time and are typically used in computer configurations that support a 64-bit or wider memory bus. Some of the physical differences between DIMMs and 72-pin SIMMs include: the length of module, the number of notches on the module, and the way the module installs in the socket. Another difference is that many 72-pin SIMMs install at a slight angle, whereas DIMMs install straight into the memory socket and remain completely vertical in relation to the system motherboard. The illustration below compares a 168-pin DIMM to a 72-pin SIMM.

*SO DIMMs

A type of memory commonly used in notebook computers is called SO DIMM or Small Outline DIMM. The principal difference between a SO DIMM and a DIMM is that the SO DIMM, because it is intended for use in notebook computers, is significantly smaller than the standard DIMM. The 72-pin SO DIMM is 32 bits wide and the 144-pin SO DIMM is 64 bits wide. 144-pin and 200-pin modules are the most common SO DIMMs today.

*MicroDIMM

(Micro Dual In-Line Memory Module) Smaller than an SO DIMM, MicroDIMMs are primarily used in sub-notebook computers. MicroDIMMs are available in 144-pin SDRAM, 172-pin DDR and 214-pin DDR2.


*RIMMS AND SO-RIMMS

RIMM is the trademarked name for a Direct Rambus memory module. RIMMs look similar to DIMMs, but have a different pin count. RIMMs transfer data in 16-bit chunks. The faster access and transfer speed generates more heat. An aluminum sheath, called a heat spreader, covers the module to protect the chips from overheating. A 184-pin Direct Rambus RIMM shown with heat spreaders pulled away.

An SO-RIMM looks similar to an SO DIMM, but it uses Rambus technology.

*FLASH MEMORY

Flash memory is a solid-state, non-volatile, rewritable memory that functions like RAM and a hard disk drive combined. Flash memory stores bits of electronic data in memory cells, just like DRAM, but it also works like a hard-disk drive in that when the power is turned off, the data remains in memory. Because of its high speed, durability, and low voltage requirements, flash memory is ideal for use in many applications - such as digital cameras, cell phones, printers, handheld computers, pagers, and audio recorders. Flash memory is available in many different form factors, including: CompactFlash, Secure Digital, SmartMedia, MultiMedia and USB Memory.

Expansion Slots
An opening in a computer where a circuit board can be inserted to add new capabilities to the computer. Nearly all personal computers except portables contain expansion slots for adding more memory, graphics capabilities, and support for special devices. The boards inserted into the expansion slots are called expansion boards, expansion cards , cards , add-ins , and add-ons.
Expansion slots for PCs come in two basic sizes: half- and full-size. Half-size slots are also called 8-bit slots because they can transfer 8 bits at a time. Full-size slots are sometimes called 16-bit slots. In addition, modern PCs include PCI slots for expansion boards that connect directly to the PCI bus.

Kinds of Expansion Slots

*ISA -- Industry Standard Architecture

*EISA -- Enhanced Industry Standard Architecture
Found in IBM-compatible desktop computers.These expansion slots are a standard way to connect more devices to a PC-compatible computer. "ISA" is an older style that is typically found on computers with 80286 ("286"), 80386 ("386") and 80486 ("486") microprocessors.

*IDE -- Intelligent Drive Electronics
Found in IBM-compatible desktop computers.IDE slots are used to connect hard disk drives and CD-ROM drives. They can be used to connect up to two different devices on each expansion slot, providing a low-cost way to add additional drives without needing another expansion card. All that is required is a cable.

*MicroChannel
Found in IBM PS/2 Desktop computers.MicroChannel slots are used to connect network cards, modems, additional memory cards and video cards, and provide specialized connections to peripheral devices. MicroChannel slots are no longer used in newer IBM computer models.
NuBus
Found in Macintosh computers.NuBus slots are used to connect many kinds of expansion cards, including network adapter cards, video cards, additional cache cards and PC computer expansion cards.

*PCI -- Peripheral Component Interconnect
Found in many IBM-compatible desktop computers and newer Macintosh computers.PCI is a standard bus adapter that allows high-speed connections to most peripheral devices, including video adapter cards, network cards, cache cards and PC computer expansion cards.

*PC Card -- (short for PCMCIA: Personal Computer Memory Card International Association)
Found in laptop computers.PC Cards conform to standards created by Personal Computer Memory Card International Association. These cards house modems, extra memory, network connectors or hard disk drives. You can find PC Cards marked as Type I, II or III, which simply designates the thickness of the card.

*SCSI - Small Computers System Interface
Found on desktop computers, predominantly in Macintoshes.SCSI expansion slots allow you to connect a wide variety of devices like CD-ROM drives, printers and scanners. You can connect up to six different SCSI devices in a chain.

*VESA - Video Electronic Standards Association
Found in IBM-compatible desktop computers.Like PCI bus expansion slots, VESA expansion slots allow for high-speed connections to peripheral devices like modems, printers and video cards.

Bus Architectures
The internal structure of a PC—the way components such as the CPU and the system bus relate to each other—is referred to as the architecture of the system.
Traditional microcomputer architecture has an internal bus that links the CPU with RAM, and an external bus that allows input/output and storage devices to connect to the system bus via expansion slots.
The System Bus
The bus in a computer system is simply a collection of physical ‘pathways’ wires that convey electrical signals between the various units in the computer.

Three Main Bus Architectures
1. Data Bus
The Data bus is simply a set of electrical lines that allow the CPU to move binary information (logic signals) to or from any part of the system components. For example, data can be transferred from memory to the Disk I/O interface via the data lines.
The number of data lines is determined the type of CPU being used.
Data Buses generally come in multiples of eight, ie. 8 bit, 16 bit, 32 bit, etc. The greater the size of the Data Bus, the greater the numbers that can be manipulated at any instant of time.


2. Address Bus
The CPU runs programs (instructions and data) that are stored in memory.
The more memory a system has, the greater the flexibility of the system in running large programs and data manipulations.
Memory is configured in such a way that each group of 8 bits (one byte) has a unique location value. This location value is generally referred to as the memory address.
The number of unique addresses that can be directly accessed by a microprocessor chip is directly related to the size of the CPU's address bus. The greater the number of address lines, the greater the number of addresses that it can access from memory.
A CPU is often compared to other CPUs by the size of the address bus or its capacity to address RAM locations.

Microprocessor
Data Bus
Address Bus
Memory
Coprocessor Inbuilt
Intel 8088
8 bit
20 bit
1 Mbyte
No
Intel 8086
16bit
20 bit
1 Mbyte
No
Intel 80286
16 bit
24 bit
16 Mbyte
No
Intel 80386SX
16bit
24 bit
16 Mbyte
No
Intel 80386
32 bit
32 bit
4096 Mbyte
No
Intel 80486SX
32 bit
32 bit
4096 Mbyte
No
Intel 80486DX
32 bit
32 bit
4096 Mbyte
Yes
Intel 80486DX2
32 bit
32 bit
4096 Mbyte
Yes
Intel 80486DX4
32 bit
32 bit
4096 Mbyte
Yes
Intel Pentium
32 bit
32 bit
4096 Mbyte
Yes



3. Control Bus
The control bus enables the CPU to monitor and maintain control of the events that occur on the Address and Data Buses.
All events that occur on the Buses are timed by a very stable clock circuit. For example, consider the case where the CPU needs to write data to memory. The basic sequence of events may be as follows:
CPU accesses the memory location by placing the address on the Address Bus.
CPU puts data on the Data Bus.
CPU selects the memory chips to be written to.
CPU activates the 'write' signal on the Control Bus.