What is Computer Architecture

 Components of a Microcomputer

A standard microcomputer consists of a microprocessor (CPU), buses, memory, parallel input/output, serial input/output, programmable I/O interrupt, and direct memory access DMA.

 Central Processing Unit (CPU)

The central processing unit (CPU) is the “brain” of the computer and is responsible for accepting data from input devices, processing the data into information, and transferring the information to memory and output devices. The CPU is organized

into the following three major sections:

1. Arithmetic logic unit (ALU)

2. Control unit

3. Registers

The function of the arithmetic logic unit (ALU) is to perform arithmetic operations such as addition, subtraction, division, and multiplication and logic operations such as AND, OR, and NOT. The function of the control unit is to control input/output devices, generate control signals to the other components of the computer such as read and write signals, and perform instruction execution. Information is moved from memory to the registers; the registers then pass the information to the ALU for logic and arithmetic operations.

 CPU Buses

When more than one wire carries the same type of information, it is called a bus. The most common buses inside a microcomputer are the address bus, the data bus, and the control bus.

 32-Bit Versus 64-Bit CPU

The size of register plays an important role in the performance of CPU. A 32-bit processor means it can perform operations on 32-bit data; therefore, the size of registers is 32 bits and ALU also performs 32-bit operations. A 64-bit CPU performs operation in 64-bit data; therefore, it contains 64-bit register and 64-bit ALU. Most desktop and server computers are using AMD and Intel processors; they might use 32 bits or 64 bits. Intel and AMD processor use the same architecture; this means a program in computer with Intel processor can run on a computer with AMD processor.

 CPU Technology

There are two types of technology used for designing CPU and they are called CISC and RIS. CISC (Complex Instruction Set Computer) In 1978, Intel developed the 8086 microprocessor chip. The 8086 was designed to process a 16-bit data word; it had  no instruction for floating point operations. At the present time, the Pentium processes 32-bit and 64-bit words, and it can process floating point instructions. Intel designed the Pentium processor in such a way that it can execute programs written for earlier 80*86 processors. The characteristics of 80 _ 86 are called complex instruction set computers (CISC), which include instructions for earlier Intel processors. Another CISC processor is VAX 11/780, which can execute programs for the PDP-11 computer. The CISC processor contains many instructions with different addressing modes, for example, the VAX 11/780 has more than 300 instructions with 16 different address modes.

 Intel Microprocessor Family

Intel designs and manufactures microprocessors for microcomputers. Each processor has a number or name, which is used by the computer designer to access the information provided by the manufacturer of the processor. Intel microprocessor IC numbers and names are 8088, 80,286, 80,386, 80,486, Pentium, Pentium II, Pentium III, and Pentium IV which they called IA-86 (Intel architecture-86). Recently Intel and HP developed a new processor called Itanium which is a 64-bit processor, which is described later in this chapter.

 Disk Controller

The disk controller moves the disk drive head, reads, and/or writes data. Today, there are two types of disk controllers: IDE (integrated disk electronics) and SCSI (small computer systems interface). Integrated Disk Electronics (IDE). An IDE disk drive is connected to the ISA bus with a flat ribbon cable. The IDE disk controller supports two hard disks, each with a 528-megabyte capacity. In 1994, hard disk drive vendors introduced EIDE (extended IDE) which supports four devices, such as hard disks, tape drives, CD-ROM devices, and larger hard disk drives. The EIDE has two connectors. Each cable is connected to the EIDE controller and can support two hard disk drives with a capacity of up to 250 GB. EIDE is used in IBM-compatible computers.

 Microcomputer Bus

There are currently a number of different computer buses on the market that are designed for microcomputers. Some of the computer BUS are ISA, MCA, EISA, VESA PCI, FireWire, USB, and PCI Express. Universal serial bus (USB) and PC Express are covered in more detail because they are more advanced than other buses.

 Type of microcomputer Bus

1. ISA Bus

The industry standard architecture (ISA) bus was introduced by IBM for the IBM PC using an 8088 microprocessor. The ISA bus has an 8-bit data bus and 20 address lines at a clock speed of 8 MHz. The PC AT type uses the 80,286 processor which has a 16-bit data bus and 24-bit address lines and is compatible with the PC.

2.Micro channel Architecture Bus

The micro channel architecture (MCA) bus was introduced by IBM in 1987 for its PS/2 microcomputer. The MCA bus is a 32-bit bus that can transfer four bytes of data at a time and runs at a 10 MHz clock speed. It also supports 16-bit data transfer and has 32-bit address lines. Micro channel architecture was so expensive the non-IBM vendors developed a comparable but less expensive solution called the EISA bus. 

3. EISA Bus

The extended ISA (EISA) bus is a 32-bit bus that also supports 8- and 16-bit data transfer bus architectures. EISA runs at 8-MHz clock speeds and has 32-bit address lines.

4. VESA Bus

The video electronics standard association (VESA) bus, which is also called a video local bus (VL-BUS), is a standard interface between the computer and its expansion. As applications became more graphically intensive, the VESA bus was introduced to maximize throughput of video graphics memory. The VESA bus provides fast data flow between stations and can transfer up to 132 Mbps.

5. PCI Bus

The peripheral component interconnect (PCI) bus was developed by Intel Corporation. PCI bus technology includes a 32-/64-bit bus that runs at a 33/66 MHz clock speed. PCI offers many advantages for connections to hubs, routers, and network interface cards (NIC). In particular, PCI provides more bandwidth: up to 1 gigabit per second as needed by these hardware components. The PCI bus was designed to improve the bandwidth and decrease latency in computer systems. Current versions of the PCI bus support data rates of 1056 Mbps and can be upgraded to 4224 Mbps. The PCI bus can support up to 16 slots or devices in the motherboard. Most suppliers of ATM (asynchronous transfer mode) and 100BaseT NICs offer a PCI interface for their products. The PCI bus can be expanded to support a 64-bit data bus. us.

6. Universal Serial BUS (USB)

The universal serial bus (USB) is a computer serial bus which enables users to connect peripherals such as the mouse, keyboard, modem, CD-ROM, scanner, and  printer, to the outside of a computer without any configuration. Personal computers equipped with USB will allow the user to connect peripherals to the computer, and the computer will automatically be configured as the devices are attached to it. This means that a USB has the capability to detect when a device has been added or removed from a PC. USB is a true plug-and-play bus.

7. PCI Express Bus

PCI express was introduced in mid-1990 with 33 MHz frequency, and during the time the speed of BUS was increased to 66 MHz. Due to new development in networking technology such as Gigabit Ethernet and I/O devices that demand more bandwidth, there is a need for a new bus technology with higher bandwidth. The PCI express was approved by Special Interest Group in 2002, and chipset starts shipping in 2004. The PCI express has the following features:

• PCI express is point-to-point connection between devices.

• PCI express is a serial bus.

• PCI express uses pocket and layer architecture.

• Compatible with PCI bus through software.

• End-to-end link data integrity (error detection).

• Isochronous data transfer.

• Select able bandwidth.