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Microprocessor and memory management

INTRODUCTION:

Now first of all we have to know about microprocessor and about memory management. we wil discuss about memory segmentation also. Microprocessor is also the heart of your computer and is the central processing unit also know as CPU. It is a computational unit and without it your computer can't work.

The working of a microprocessor is as follows: The computer you are using to read this page uses a microprocessor to do its work. The microprocessor is the heart of any normal computer, whether it is a desktop machine, a server or a laptop. The microprocessor you are using might be a Pentium, a K6, a PowerPC, a Spark or any of the many other brands and types of microprocessors, but they all do approximately the same thing in approximately the same way. A microprocessor -- also known as a CPU or central processing unit -- is a complete computation engine that is fabricated on a single chip. The first microprocessor was the Intel 4004, introduced in 1971. The 4004 was not very powerful -- all it could do was add and subtract, and it could only do that 4 bits at a time. But it was amazing that everything was on one chip.

Microprocessor:

Amicroprocessorincorporates most or all of the functions of acentral processing unit(CPU) on a singleintegrated circuit(IC).The first microprocessors emerged in the early 1970s and were used for electroniccalculators, usingbinary-coded decimal(BCD) arithmetic on 4-bitwords. Otherembeddeduses of 4- and 8-bit microprocessors, such asterminals,printers, various kinds of automationetc, followed rather quickly. Affordable 8-bit microprocessors with 16-bit addressing also led to the first general purpose microcomputersin the mid-1970s.

Computer processors were for a long period constructed out of small and medium-scale ICs containing the equivalent of a few to a few hundred transistors. The integration of the whole CPU onto a single chip therefore greatly reduced the cost of processing capacity. From their humble beginnings, continued increases in microprocessor capacity have rendered other forms of computers almost completely obsolete (seehistory of computing hardware), with one or more microprocessor as processing element in everything from the smallestembedded systemsandhandheld devicesto the largestmainframesandsupercomputers.

Since the early 1970s, the increase in capacity of microprocessors has been known to generally followMoore's Law, which suggests that the complexity of an integrated circuit, with respect to minimum component cost, doubles every two years.In the late 1990s, and in the high-performance microprocessor segment, heat generation (TDP), due to switching losses, static current leakage, and other factors, emerged as a leading developmental constraint.

HOW IT COMES IN EXISTANCE

This is interesting to note thatthe microprocessorhad existed for only 10 years prior to the creation of the PC! Intel inventedthe microprocessorin 1971; the PC was created by IBM in 1981. Now more than 20 years later, we are still using systems based more or less on the design of that first PC. The processors powering our PCs today are still backward compatible in many ways with the 8088 that IBM selected for the first PC in 1981.November 15, 2001 marked the 30th anniversary ofthe microprocessor, and in those 30 years processor speed has increased more than 18,500 times (from 0.108MHz to 2GHz).The 4004 was introduced on November 15, 1971 and originally ran at a clock speed of 108KHz (108,000 cycles per second, or just over one-tenth a megahertz). The 4004 contained 2,300 transistors and was built on a 10-micron process. This means that each line, trace, or transistor could be spaced about 10 microns (millionths of a meter) apart. Data was transferred 4 bits at a time, and the maximum addressable memory was only 640 bytes. The 4004 was designed for use in a calculator but proved to be useful for many other functions because of its inherent programmability. For example, the 4004 was used in traffic light controllers, blood analyzers, and even in the NASA Pioneer 10 deep space probe!

In April 1972, Intel released the 8008 processor, which originally ran at a clock speed of 200KHz (0.2MHz). The 8008 processor contained 3,500 transistors and was built on the same 10-micron process as the previous processor. The big change in the 8008 was that it had an 8-bit data bus, which meant it could move data 8 bits at a timetwice as much as the previous chip. It could also address more memory, up to 16KB. This chip was primarily used in dumb terminals and general-purpose calculators.

The next chip in the lineup was the 8080, introduced in April 1974, running at a clock rate of 2MHz. Due mostly to the faster clock rate, the 8080 processor had 10 times the performance of the 8008. The 8080 chip contained 6,000 transistors and was built on a 6-micron process. Similar to the previous chip, the 8080 had an 8-bit data bus, so it could transfer 8 bits of data at a time. The 8080 could address up to 64KB of memory, significantly more than the previous chip.

This was the 8080 that helped start the PC revolution because this was the processor chip used in what is generally regarded as the first personal computer, the Altair 8800. The CP/M operating system was written for the 8080 chip, and Microsoft was founded and delivered its first product: Microsoft BASIC for the Altair. These initial tools provided the foundation for a revolution in software because thousands of programs were written to run on this platform.

In fact, the 8080 became so popular that it was cloned. A company called Zilog formed in late 1975, joined by several ex-Intel 8080 engineers. In July 1976, it released the Z-80 processor, which was a vastly improved version of the 8080. It was not pin compatible but instead combined functions such as the memory interface and RAM refresh circuitry, which enabled cheaper and simpler systems to be designed. The Z-80 also incorporated a superset of 8080 instructions, meaning it could run all 8080 programs. It also included new instructions and new internal registers, so software designed for the Z-80 would not necessarily run on the older 8080. The Z-80 ran initially at 2.5MHz (later versions ran up to 10MHz) and contained 8,500 transistors. The Z-80 could access 64KB of memory.

RadioShack selected the Z-80 for the TRS-80 Model 1, its first PC. The chip also was the first to be used by many pioneering systems, including the Osborne and Kaypro machines. Other companies followed, and soon the Z-80 was the standard processor for systems running the CP/M operating system and the popular software of the day.

Intel released the 8085, its follow-up to the 8080, in March 1976. Even though it predated the Z-80 by several months, it never achieved the popularity of the Z-80 in personal computer systems. It was popular as an embedded controller, finding use in scales and other computerized equipment. The 8085 ran at 5MHz and contained 6,500 transistors. It was built on a 3-micron process and incorporated an 8-bit data bus.

Along different architectural lines, MOS Technologies introduced the 6502 in 1976. This chip was designed by several ex-Motorola engineers who had worked on Motorola's first processor, the 6800. The 6502 was an 8-bit processor like the 8080, but it sold for around $25, whereas the 8080 cost about $300 when it was introduced. The price appealed to Steve Wozniak, who placed the chip in his Apple I and Apple II designs. The chip was also used in systems by Commodore and other system manufacturers. The 6502 and its successors were also used in game consoles, including the originalNintendo Entertainment System(NES) among others. Motorola went on to create the 68000 series, which became the basis for the Apple Macintosh line of computers. Today those systems use the PowerPC chip, also by Motorola and a successor to the 68000 series.

All these previous chips set the stage for the first PC processors. Intel introduced the 8086 in June 1978. The 8086 chip brought with it the original x86 instruction set that is still present in current x86-compatible chips such as the Pentium 4 and AMD Athlon. A dramatic improvement over the previous chips, the 8086 was a full 16-bit design with 16-bit internal registers and a 16-bit data bus. This meant that it could work on 16-bit numbers and data internally and also transfer 16 bits at a time in and out of the chip. The 8086 contained 29,000 transistors and initially ran at up to 5MHz.

The chip also used 20-bit addressing, so it could directly address up to 1MB of memory. Although not directly backward compatible with the 8080, the 8086 instructions and language were very similar and enabled older programs to quickly be ported over to run. This later proved important to help jumpstart the PC software revolution with recycled CP/M (8080) software.

Although the 8086 was a great chip, it was expensive at the time and more importantly required expensive 16-bit board designs and infrastructure to support it. To help bring costs down, in 1979 Intel released what some called a crippled version of the 8086 called the 8088. The 8088 processor used the same internal core as the 8086, had the same 16-bit registers, and could address the same 1MB of memory, but the external data bus was reduced to 8 bits. This enabled support chips from the older 8-bit 8085 to be used, and far less expensive boards and systems could be made. These reasons are why IBM chose the 8088 instead of the 8086 for the first PC.

This decision would affect history in several ways. The 8088 was fully software compatible with the 8086, so it could run 16-bit software. Also, because the instruction set was very similar to the previous 8085 and 8080, programs written for those older chips could be quickly and easily modified to run. This enabled a large library of programs to be quickly released for the IBM PC, thus helping it become a success. The overwhelming blockbuster success of the IBM PC left in its wake the legacy of requiring backward compatibility with it. To maintain the momentum, Intel has pretty much been forced to maintain backward compatibility with the 8088/8086 in most of the processors it has released since then.

To date, backward compatibility has been maintained, but innovating and adding new features has still been possible. One major change in processors was the move from the 16-bit internal architecture of the 286 and earlier processors to the 32-bit internal architecture of the 386 and later chips, which Intel calls IA-32 (Intel Architecture, 32-bit). Intel's 32-bit architecture dates to 1985, and it took a full 10 years for both a partial 32-bit mainstream OS (Windows 95) as well as a full 32-bit OS requiring 32-bit drivers (Windows NT) to surface, and another 6 years for the mainstream to shift to a fully 32-bit environment for the OS and drivers (Windows XP). That's a total of 16 years from the release of 32-bit computing hardware to the full adoption of 32-bit computing in the mainstream with supporting software. I'm sure you can appreciate that 16 years is a lifetime in technology.

Now we are in the midst of another major architectural jump, as Intel and AMD are in the process of moving from 32-bit to 64-bit computing for servers, desktop PCs, and even portable PCs. Intel had introduced the IA-64 (Intel Architecture, 64-bit) in the form of the Itanium and Itanium 2 processors several years earlier, but this standard was something completely new and not an extension of the existing 32-bit technology. IA-64 was first announced in 1994 as a CPU development project with Intel and HP (codenamed Merced), and the first technical details were made available in October 1997. The result was the IA-64 architecture and Itanium chip, which was officially released in 2001.

The fact that the IA-64 architecture is not an extension of IA-32 but is instead a whole new and completely different architecture is fine for non-PC environments such as servers (for which IA-64 was designed), but the PC market has always hinged on backward compatibility. Even though emulating IA-32 within IA-64 is possible, such emulation and support is slow.

With the door now open, AMD seized this opportunity to develop 64-bit extensions to IA-32, which it calls AMD64 (originally known as x86-64). Intel eventually released its own set of 64-bit extensions, which it calls EM64T or IA-32e mode. As it turns out, the Intel extensions are almost identical to the AMD extensions, meaning they are software compatible. It seems for the first time that Intel has unarguably followed AMD's lead in the development of PC architecture.

To make 64-bit computing a reality, 64-bit operating systems and 64-bit drivers are also needed. Microsoft began providing trial versions of Windows XP Professional x64 Edition (which supports AMD64 and EM64T) in April 2005, and major computer vendors now offer systems with Windows XP Professional x64 already installed. Major hardware vendors have also developed 64-bit drivers for current and recent hardware. Linux is also available in 64-bitcompatible versions, making the move to 64-bit computing possible.

The latest development is the introduction of dual-core processors from both Intel and AMD. Dual-core processors have two full CPU cores operating off of one CPU packagein essence enabling a single processor to perform the work of two processors. Although dual-core processors don't make games (which use single execution threads and are usually not run with other applications) play faster, dual-core processors, like multiple single-core processors, split up the workload caused by running multiple applications at the same time. If you've ever tried to scan for viruses while checking email or running another application, you've probably seen how running multiple applications can bring even the fastest processor to its knees. With dual-core processors available from both Intel and AMD, your ability to get more work done in less time by multitasking is greatly enhanced. Current dual-core processors also support AMD64 or EM64T 64-bit extensions, enabling you to enjoy both dual-core and 64-bit computing's advantages.

Memory management

What is memory management?

It is the act of managingcomputer memory. In its simpler forms, this involves providing ways to allocate portions of memory to programs at their request, and freeing it for reuse when no longer needed. The management of main memory is critical to the computer system.

Virtual memory:

Now we have to know about virtual mamory.

This systems separate the memory addresses used by a process from actual physical addresses, allowing separation of processes and increasing the effectively available amount of RAM usingdisk swapping. The quality of the virtual memory manager can have a big impact on overall system performance.

Garbage collection:

It is the automated allocation, and deallocation of computer memory resources for a program. This is generally implemented at the programming language level and is in opposition tomanual memory management, the explicit allocation and deallocation of computer memory resources.

FEATURES

Memory management systems onmulti-tasking operating systemsusually deal with the following issues.

Relocation

In systems withvirtual memory, programs in memory must be able to reside in different parts of the memory at different times. This is because when the program is swapped back into memory after being swapped out for a while it can not always be placed in the same location. The virtual memory management unit must also deal with concurrency. Memory management in the operating system should therefore be able to relocate programs in memory and handle memory references and addresses in the code of the program so that they always point to the right location in memory.

Protection

Processes should not be able to reference the memory for another process without permission. This is calledmemory protection, and prevents malicious or malfunctioning code in one program from interfering with the operation of other running programs.

Sharing

Even though the memory for different processes is normally protected from each other, different processes sometimes need to be able to share information and therefore access the same part of memory. Shared memory is one of the fastest techniques forInter-process communication.

Logical organization

Programs are often organized in modules. Some of these modules could be shared between different programs, some are read only and some contain data that can be modified. The memory management is responsible for handling this logical organization that is different from the physical linear address space. One way to arrange this organization issegmentation.

Physical organization

Memory is usually divided into fastprimary storageand slowsecondary storage. Memory management in the operating system handles moving information between these two levels of memory.

Memory compaction

The technique of relocating all occupied areas of memory to one end of the memory so as to get one large block of free memory space is called compaction.

Memory can be compacted under the following conditions:

1. As soon as a job terminates.

2. When a new job cannot be loaded into memory due to fragmentation.

3. At fixed time intervals.

MICROPROCESSOR AND MEMORY MANAGEMENT:

At the most primitive level, a computer consists of a microprocessor, which executes instructions, and a memory, in which those instructions (and other data) is stored.Figure shows a block diagram of these two components. The diagram shows four types of wires that connect the microprocessor and the memory:

Address Bus:

These wires are controlled by the microprocessor to select a particular location in memory for reading or writing.

The 6.270 board uses a memory chip that has 15 address wires. Since each wire has two states (it can be a digital one or a zero), 2 to the 15th power locations are possible. 215 is precisely 32,768 locations; thus, the system has 32K of memory.

Data Bus.:

These wires are used to pass data between the microprocessor and the memory. When data is written to the memory, the microprocessor drives these wires; when data is read from the memory, the memory drives the wires.

In our example (and in the 6.270 board), there are eight data wires (or bits).

These wires can transfer 28 or 256 di_erent values per transaction. This data word of 8 bits is commonly referred to as a byte

Read/Write Control Line :

This single wire is driven by the microprocessor to control the function of the memory. If the wire is logic true, then the memory performs a \read" operation. If the wire is logic zero, then the memory performs a \write operation."

Memory Enable Control Line.

This wire, also called the E clock, connects to the enable circuitry of the memory. When the memory is enabled, it performs either a read or write operation as determined by the read/write line.

Multiplexing Data and Address Signals

Things are a little more complex with the particular microprocessor that is used in the 6.270 board, the Motorola 6811. On the 6811, The eight data bus wires take turns functioning as address wires as well. When a memory location is needed (for reading or writing), _rest the data wires function as address wires, transmitting the eight lower-order bits of the address.

Then they function as data wires, either transmitting a data byte (for a write cycle) or receiving a data byte (for a read cycle). All this happens very fast; 2 million times per second to be exact. The memory needs to help to deal with the split-personality data/address bus. This help comes in the form of an 8-bit latch. This chip (the 74HC373) performs the function of latching, or storing, the 8 address values so that the memory will have the full 15-bit address available for reading or writing data.

An additional signal, the Address Strobe output of the microprocessor, tells the latch when to grab hold of the address values from the address/data bus.

When the full 15-bit address is available to the memory (7 bits direct from the microprocessor and 8 bits from the latch), the read or write transaction can occur. Because the address/data bus is also wired directly to the memory, data can flow in either direction between the memory and the microprocessor. This whole process |the transmitting of the lower address bits, the latching of these bits, and then a read or write transaction with the memory is orchestrated by the microprocessor. The E clock, the Read/Write line, and the Address Strobe line perform in tight synchronization to make sure these operations happen in the correct sequence and within the timing capacities of the actual chip hardware.

Memory Mapping:

So far we have seen how a memory can be connected to the address space of a microprocessor. In a circuit like the one of the 6.270 board, the microprocessor must interact with other devices than the memory for example, motors and sensors.

A typical solution uses 8-bit latches for input and output. These latches are connected to the data bus of the microprocessor so that they appear like a location in memory. Then, the act of reading or writing from one of these memory locations causes data to be read from or written to a latch|to which the external devices are connected.

The '374 has outputs that control the motors (through chips labelled \L293," which will be discussed later). The digital sensors are driven into the data bus by a chip labelled \244." On the expansion board, another 374 chip is used for eight bits of digital output.

These interface latch chips are used in a technique called memory mapping. The chips are \mapped" to a particular address in the microprocessor's memory.

The following discussion will show how both the 32k RAM memory and the digital input and output latch chips share the address space of the microprocessor.

REFERENCES:

1. Sun 68000 Board User's Manual, Sun Microsystems

2. U.S.SHAH'S Microprocessor and its applications.

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