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--- en:multiasm:cs:chapter_3_1 [2025/01/03 12:51] – ktokarz
+++ en:multiasm:cs:chapter_3_1 [2025/11/28 09:02] (current) – [Buses] ktokarz
@@ Line 1: / Line 1: @@
 ====== Overall View on Computer Architecture: Processor, Memory, IO, Buses ======
-The computers which we use every day are all designed based on the same general idea of cooperation of three base elements processor, memory and peripheral devices. Their names represent their functions in the system. The memory stores the data and program code, the processor manipulates the data by executing programs, and peripherals are used to keep the contact with the user, environment and other systems. To exchange the information these elements are connected together by interconnections named buses. The generic block schematic diagram of the exemplary computer is shown in Fig. {{ref>compblock}}.
+The computers we use every day are all designed around the same general idea of cooperation among three base elements: processor, memory and peripheral devices. Their names represent their functions in the system: memory stores data and program code, the processor manipulates data by executing programs, and peripherals maintain contact with the user, the environment and other systems. To exchange information, these elements communicate through interconnections named buses. The generic block schematic diagram of the exemplary computer is shown in Fig. {{ref>compblock}}.
 <figure compblock>
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 ===== Processor =====
-It is often called “the brain” of the computer. Although it doesn’t think, the processor is the element which controls all other units of the computer. The processor is the device that manages everything in the machine. Every hardware part of the computer is controlled more or less by the main processor. Even if the device has its own processor - for example keyboard - it works under the control of the main one. Processor handles events. We can say that synchronous events are those that which processor handles periodically. The processor can’t stop. Of course when it has the power. But even when you don’t see anything special happening on the screen. In PC computer in an operating system without a graphical user interface, for example, plain Linux, or a command box in Windows, if you see only „C:\>” the processor works. In this situation, it executes the main loop of the system. In such a loop, it’s waiting for the asynchronous events. Such an asynchronous event occurs when the user pushes the key or moves the mouse, when the sound card stops playing one sound, the hard disk ends up transmitting the data. For all of those actions the processor handles executing the programs - or if you prefer – procedures.
+It is often called “the brain” of the computer. Although it doesn’t think, the processor is the element which controls all other units of the computer. The processor is the device that manages everything in the machine. Every hardware part of the computer is controlled more or less by the main processor. Even if the device has its own processor - for example, a keyboard - it works under the control of the main one. The processor handles events. We can say that synchronous events are those that the processor handles periodically. The processor can’t stop. Of course, when it has the power, even when you don’t see anything special happening on the screen. In PC computer in an operating system without a graphical user interface, for example, plain Linux, or a command box in Windows, if you see only „C:\>”, the processor works. In this situation, it executes the main loop of the system. In such a loop, it’s waiting for the asynchronous events. Such an asynchronous event occurs when the user pushes a key or moves the mouse, when the sound card stops playing a sound, or when the hard disk ends up transmitting the data. For all of those actions, the processor handles executing the programs - or, if you prefer, procedures.
-Processor is characterised by its main parameters including the frequency of operation, class, …
-Frequency is very important information which tells the user how many instructions can be executed in the time unit. To have the detailed information of a real number of instructions per second it must be combined with the average number of clock pulses required to execute the instruction. Older processors needed a few or even a dozen pulses of clock for a single instruction. Modern machines, thanks to parallel execution can achieve impressive results of a few instructions per single cycle.
-The class of the processor tells what is the number of bits in the data word. It means what is the size of the arguments of the data which the processor can calculate with a single arithmetic, logic or other operation. The still popular 8-bit machines have a data length of 8 bits, while most sophisticated can use 32 or 64-bit arguments. The class of the processor determines the size of its internal data registers, the size of arguments of instructions and the number of lines of the data bus.
-<info box> Some modern 64-bit processors have additional registers much longer than the ones in the main set. For example, in x64 architecture, there are ZMM registers of 512 bits length. </info box>
+A processor is characterised by its main parameters, including its operating frequency and class.
+Frequency is crucial information which tells the user how many operations can be executed in a time unit. To have the detailed information of a real number of instructions per second, it must be combined with the average number of clock pulses required to execute the instruction. Older processors required a few or even a dozen clock pulses per instruction. Modern machines, thanks to parallel execution, can achieve impressive results of a few instructions per single cycle.
+The processor's class indicates the number of bits in the data word. It tells us what the size of the arguments the processor can calculate with a single arithmetic, logic or other operation. The still-popular 8-bit machines have a data length of 8 bits, while the most sophisticated can use 32 or 64-bit arguments. The processor's class determines the size of its internal data registers, the size of instructions' arguments and the number of data bus lines.
+<note info> Some modern 64-bit processors have additional registers much longer than the ones in the main set. For example, in the x64 architecture, there are ZMM registers that are 512 bits in length. </note>
+===== Memory =====
+Memory is the element of the computer that stores data and programs. It is visible to the processor as a sequence of data words, where every word has its own address. Addressing allows the processor to access simple and complex variables and to read the instructions for execution. Although intuitively, the size of a memory word should correspond to the class of the processor, it is not always true. For example, in PCs, independently of the processor class, the memory is always organised as a sequence of bytes and the size of it is provided in megabytes or gigabytes.
+<note info> The byte is historically assumed as 8 bits of information and used as the base unit to express the size of data in the world of computers. </note>
+The size of the memory installed on the computer does not have to correspond to the size of the address space, the maximal size of the memory which is addressable by the processor. In modern machines, it would be impossible or hardly achievable. For example, for x64 architecture, the theoretical address space is 2^64 (16 exabytes). Even the address space currently supported by processors' hardware is as large as 2^48, which equals 256 terabytes. On the opposite side, in constrained devices, the size of the physical memory can be bigger than supported by the processor. To enable access to a bigger memory than the addressing space of the processor or to support flexible placement of programs in a big address space, the paging mechanism is used. It is a hardware support unit for mapping the address used by the processor into the physical memory installed in the computer.
+<note info> To learn more about paging please refer to https://connormcgarr.github.io/paging/ </note>
+===== Peripherals =====
+Called also input-output (I/O) devices. There is a variety of units belonging to this group. It includes timers, communication ports, general-purpose inputs and outputs, displays, network controllers, video and audio modules, data storage controllers and many others. The main function of peripheral modules is to exchange information between the computer and the user, collect information from the environment, send and receive data to and from elements of the computer not connected directly to the processor, and exchange data with other computers and systems. Some of them are used to connect the processor to the functional unit of the same computer. For example, the hard disk drive is not connected directly to the processor. It uses the specialised controller, which is the peripheral module operating as an interface between the central elements of the computer and the hard drive. Another example can be the display. It uses a graphics card, which plays the role of a peripheral interface between the computer and the monitor.
+===== Buses =====
+The processor, memory and peripherals exchange information using interconnections called buses. Although you can find in the literature and on the internet a variety of bus types and their names, at the very lowest level, there are three buses connecting the processor, memory, and peripherals.
+**Address bus** delivers the address generated by the processor to memory or peripherals. This address specifies the single memory cell or peripheral register that the processor wants to access. The address bus is used not only to address the data which the processor wants to transmit to or from memory or a peripheral. Instructions are also stored in memory, so the address bus also selects the instruction that the processor fetches and later executes. The address bus is one-directional. The address is generated by the processor and delivered to other units.
+<note info> If there is a DMA controller in the computer, in some circumstances, it can also generate an address instead of the processor. Refer to the chapter with the DMA description. </note>
+The number of lines in the address bus is fixed for the processor and determines the size of the addressing space the processor can access. For example, if the address bus of some processor has 16 lines, it can generate up to 16^2 = 65536 different addresses.
+**Data bus** is used to exchange data between the processor and the memory or peripherals. The processor can read the data from memory or peripherals, or write the data to these units, previously sending their address with the address bus. As data can be read or written, the data bus is bi-directional.
+<note info> In the systems with a DMA controller, the data bus is utilised to exchange data between memory and peripherals directly. Refer to the chapter with the DMA description. </note>
+The number of bits of the data bus usually corresponds to the class of the processor. It means that an 8-bit class processor has 8 lines of the data bus.
+**Control bus** is formed by lines mainly used for synchronisation between the elements of the computer. In the minimal implementation, it includes the read and write lines. Read line (#RD) is the information to other elements that the processor wants to read the data from the unit. In such a situation, the element, e.g. memory, puts the data from the addressed cell on the data bus. Active write signal (#WR) informs the element that the data which is present on the data bus should be stored at the specified address.
+The control bus can also include other signals specific to the system, e.g. interrupt signals, DMA control lines, clock pulses, signals distinguishing the memory and peripheral access, signals activating chosen modules and others.

en/multiasm/cs/chapter_3_1.1735908693.txt.gz · Last modified: 2025/01/03 12:51 by ktokarz