Computers: Microprocessors and computers

By -

Microprocessors and computers

Any suitable type of switch can be used to build up the logic gate circuits used in the central processing units (CPUs) of computers. However, because many thousands are required to construct circuits for even the simplest computer, it is important that they should be small, reliable, cheap, and consume little power. Back in the 1940s and 1950s, there were very few computers, and those that existed were very large, expensive, and unreliable. This was because glass valves were used as switches inside their CPUs. The devel­ opment of the transistor, used in today's microprocessors, brought about the revolution in switch technology needed for the spread of computing.

In the future, other types of switching device may prove viable. Some institutions are currently working on optical computers, using pulses of laser light instead of pulses of electrons to communicate the Os and 1s of binary code. By constructing optical AND, OR and NOT gates they have demonstrated the feasibility of such computers, and their potential advantages are apparent when you consider that:

• No electrical wires will be needed, which will reduce the cost.

• Their speed will surpass that of electronic computers, as the information will travel at the speed of light.

However, optical computers have a long way to go to catch up with the high volume and low-cost production of micro­ processors, and the present-day type of computer, using microprocessors as CPUs, will certainly reign supreme up to the end of this century.

There are a number of different microprocessor designs ('architectures') used for computer CPUs. Some, such as the Motorola 68000 series of microchips, contain an arrange­ ment of logic circuits more suited for graphical applications, and so are used on the Apple Macintosh, the Atara ST, and the Amiga computers. Others, such as the Intel 80x86 series of chips, are more suitable for processing numerical data and text, and are used on the successors to the original IBM PC. Having said that, the latest generations of such chips are so powerful that there is little practical difference in their respective abilities to handle graphical or numerical applications, and the Apple Macintosh and the IBM PC's successors now run very similar software. If a software package proves a major success on one system, it's not long before it is converted to run on the other.

The most popular makes of CPU chips are described in the sections below. Each new generation may contain sev­ eral times as many transistors as its predecessors, indicative of the fact that it has a greater number of and more complex logic circuits. Amongst other things, these enable it to:

• Carry out operations at higher speeds.

• Perform calculations to more significant figures (i.e. a higher degree of accuracy).

• Directly address more memory (and therefore support more complex software).

An important factor which affects all these is the number of bits that the CPU is able to process simultaneously. In the 1970s, the standard was 8-bit CPUs, whereas today it is 32- bits. This implies not only many more transistors in today's microprocessors, but also many more parallel wires in the data buses (cables) inside the computer. To keep costs down, some computers contain 32-bit chips but 16-bit data buses, i.e. the chips process data 32 bits at a time, but communicate data only 16 bits at a time. (This kind of restriction will disappear if optical computers become a reality.)

clip_image002

The Z80 microprocessor

This microchip, manufactured by Zilog, was the main CPU used in microcomputers in the 1970s and early 1980s. It is still used today in some low-priced computers such as the Amstrad PCW word processor. An enormous amount of business software has been written for computers which use this chip, and much of it is very cheap or even free.

The Z80 is, however, an 8-bit chip, and therefore of limited power. It is slow, and able to access only 64 Kbytes of memory. The result is that software running on Z80- based computers is no match for the kind of thing that is now available on more up-to-date machines.

The 680x0 family of microprocessors

These are 32-bit microprocessors from Motorola. They appeared in the mid-1980s, and are used on computers which are strong on graphics such as the Apple Macintosh, the Atari ST, and the Amiga. The original chip, used on the first Apple Mac, was the 68000, the latest model (at the time of writing) is the 68040.

These chips are fast, and able to access many Gigabytes of memory.

The 80x86 family of microprocessors

These microprocessors, from Intel, are the most widely used, being the ones adopted by the IBM PC and its successors. 'Clones' of these chips are also available from other manufacturers. Most PCs today, whether 'compati­ bles' from the likes of Toshiba, Tandon, Olivetti, and Amstrad, or PS/2 machines from IBM itself, use these chips. In future I shall use the term 'PC' to mean personal computers of this type, as distinct from other microcompu­ ters such as the Apple Macintosh.

The 8086 chip, used on earlier models of the IBM PC (at the beginning of the 1980s), was a 16-bit chip. It was therefore faster than the Z80 (which it effectively replaced), and could access 640K of memory. When the IBM PC first appeared, all business software on microcomputers was designed to run within 64K, and the potential to access ten times this amount seemed more than generous. Today, it seems paltry.

In the mid-1980s IBM produced a more advanced version of the PC called the AT (see page 48). This boasted the latest 32-bit 80286 chip which was capable, in theory, of accessing many Megabytes of memory (32Mb in fact). Unfortunately, the operating system used on PCs limited it to 640K (see Chapter 5), and in any case the chip itself turned out to be 'brain damaged' and not capable of fulfilling these expectations. Today, the much more powerful 80386 and 80486 chips are with us, with none of these memory limitations. At the time of writing the operating system still restricts memory access, but operating environments such as Win­ dows break the 640K memory barrier (see Chapter 5).

During the 1980s, Intel chips gradually came to dominate the computer market. At the time of writing (late 1990), they account for some 40% of the market, and many analysts reckon that by the end of the century they will account for over 80%.

Comments

Post a Comment

Popular posts from this blog

The Conversion Cycle:The Traditional Manufacturing Environment

By -
Image
The Traditional Manufacturing Environment The conversion cycle consists of both physical and information activities related to manufacturing products for sale. The context-level data flow diagram (DFD) in Figure 7-1 illustrates the central role of the conversion cycle and its interactions with other business cycles. Production is triggered by customer orders from the revenue cycle and/or by sales forecasts from marketing. These inputs are used to set a production target and prepare a production plan, which drives production activities. Purchase requisitions for the raw materials needed to meet production objectives are sent to the purchases procedures (expenditure cycle), which prepares purchase orders for vendors. Labor used in production is transmitted to the payroll system (expenditure cycle) for payroll processing. Manufacturing costs associated with intermediate work-in-process and finished goods (FG) are sent to the general ledger (GL) and financial reporting system. Dependin
Read more

The Revenue Cycle:Manual Systems

By -
Image
Manual Systems The purpose of this section is to support the system concepts presented in the previous section with models depicting people, organizational units, and physical documents and files. This section should help you envision the segregation of duties and independent verifications, which are essential to effective internal control regardless of the technology in place. In addition, we highlight inefficiencies intrinsic to manual systems, which gave rise to modern systems using improved technologies. SALES ORDER PROCESSING The system flowchart in Figure 4-12 shows the procedures and the documents typical to a manual sales order system. In manual systems, maintaining physical files of source documents is critical to the audit trail. As we walk through the flowchart, notice that in each department, after completion of the assigned task, one or more documents are filed as evidence that the task was completed. Sales Department The sales process begins with a customer cont
Read more

HIPO (hierarchy plus input-process-output)

By -
Image
HIPO (hierarchy plus input-process-output) 64.1 Purpose The HIPO (Hierarchy plus Input-Process-Output) technique is a tool for planning and/or documenting a computer program. A HIPO model consists of a hierarchy chart that graphically represents the program’s control structure and a set of IPO (Input-Process-Output) charts that describe the inputs to, the outputs from, and the functions (or processes) performed by each module on the hierarchy chart. 64.2 Strengths, weaknesses, and limitations Using the HIPO technique, designers can evaluate and refine a program’s design, and correct flaws prior to implementation. Given the graphic nature of HIPO, users and managers can easily follow a program’s structure. The hierarchy chart serves as a useful planning and visualization document for managing the program development process. The IPO charts define for the programmer each module’s inputs, outputs, and algorithms. In theory, HIPO provides valuable long-term documentation. However
Read more