Lecture 7: System Integration and Performance

Memory Size and Memory Access Speed

Because every program occupies some amount of space in RAM, a large amount of RAM is essential to operate with multiple programs. Furthermore, RAM size significantly affects computer speed because information is frequently written to and retrieved from RAM. If there is insufficient RAM space, the computer must frequently resort to using its hard disk, a device with slower access speed than RAM, which results in diminished performance. The higher the read/write speed, the faster the computer is.

Bus Width and Bus Speed

A computer with a large bus width can generally carry more bits at a time between computer components, such as between main memory and the CPU, making it faster than a computer with a small bus width. Bus speed, which is measured in hertz (Hz), also affects computing performance.

Instruction Set

A computer's CPU is typically based on a complex instruction set computer (CISC) architecture, or a reduced instruction set computer (RISC) architecture, or a mixed architecture. The difference between them is the number of clock cycles it takes to execute a single instruction. Some computer architectures require more cycles to execute the same instruction than others.

Bus Master and Slave

A device that can take control of the system bus is called a bus master, and a device that can only respond to a transaction initiated by a remote bus master is called a bus slave. Example: CPU is the master and Memory is the slave.

IEEE 1394 (FireWire)

A serial interface connector introduced in 2000 for connecting digital devices. Apple's version of this standard, branded Firewire 400, has a data transfer rate of 400 Mbits/sec. Firewire 800 (IEEE 1394b) has a data transfer rate of 800 Mbits/sec.

Parallel Transmission

A type of data transmission in which bytes of data are transmitted at one time, with the bits in each byte taking a separate path. Parallel buses require multiple data lines (wires) and correspondingly complex plugsocket arrangements and cables; A serial bus carries data one bit at a time using two signal paths, one for the data and one for the ACK

Serial Transmission

A type of data transmission in which the bits in a byte travel down the same path one after the other.

Approach for Transferring Data without CPU

Direct Memory access (DMA)--method for transferring data between main memory and an I/O device that bypasses the cpu.

Components in a CPU-Memory-I/O Pathway

Except for a single pieces of input or output that can be transferred directly from a register, data from input or intended for output is normally stored at least temporarily in memory. The I/O modules (or called I/O controllers) act as interfaces between the CPU/memory and I/O devices.

Battery on the Motherboard

In the picture on last page, the CMOS battery powers the Real Time Clock (RTC) chip, an integrated circuit on the motherboard. The RTC provides an accurate date and time, in addition to allowing a computer to regulate the timing and speed of all of its functions. When the computer boots up, part of the process is to query the RTC to get the correct time and date. Many modern computers store the BIOS settings in non-volatile RAM that works without any power at all. if the battery goes dead, the clock fails but the computer can still boot using the information in the non-volatile RAM area.

Number of CPUs

Incorporating more than one microprocessor increases a computer's processing power and speed because it can perform multitasking. Some computers have dual-core processors, quad-core architecture, or other multi-core processors. Besides multi-core computers, multiprocessor computers are also available.

I/O bus

Input/ Output bus connects the expansion slots (ports) to Processor. Typically longer than memory bus. Compatible with many different architectures. Ex: keyboard (input), mouste (input), scanner (input, USB (input or output).

Data Lines

Lines of a bus dedicated to moving data are called data bus. Data lines contain the actual information that must be moved from one location to another.

Factors That Affect Computer Performance

Many people think that the higher the CPU speed, the faster the computer. Some of the key factors that affect computer performance are shown in the following list: word size, bus width and bus speed, chip set, number of CPUs.

Mini-SATA

Mini-SATA, or mSATA, is a low-profile interface connector that enables more effective SATA integration in small form-factor drives roughly the size of a business card, such as solid state drives (SSDs). An mSATA SSD has a smaller form factor than a standard SSD and is designed for use with portable, power-constrained devices such as laptops, tablets and netbooks.

External Port: RJ-45

Network Ethernet port: a RJ-45 port, used by a network cable to connect the computer to the wired LAN (Ethernet). RJ-45 connector is an 8 pin - 8 contact (8P - 8C) type modular connector. The latest Ethernet technology is called Gigabit Ethernet and supports a data transfer rate of over 10Gigabits per second.

Storage Interface: PCI Express

PCIe is attractive because of its flexible architecture and fast signaling rate. Full-width PCIe is faster than SATA. M.2 is a connector standard for mobile SSDs. M.2 connector can plug in both PCIe-based and SATA-based SSDs, but is generally PCIe-based only.

External Port: PS/2

PS/2 port, also called a mini-DIN port, is a round 6-pin port used by a keyboard or mouse. The ports look alike but are not interchangeable. On a PC, the purple port is for the keyboard, and the green port is for the mouse. PS/2 port is now considered a legacy port as USB port has superseded it and very few of the modern motherboards include it as a legacy port.

Two Types of ATA Interface

Parallel ATA (PATA) and Serial ATA (SATA)

Why Serial Bus is Faster for High Data Rate Transmission?

Parallel bus are subject to radio-generated electrical interference between different lines at high data transfer rates. The higher the data rate, the worse the interference, which limits their speed and length. For many applications, the throughput for serial buses is higher than for parallel because of the lack of electrical interference.

Device Controllers

Peripheral devices are connected to a bus via a device controller. Implements: bus protocol, translation between bus and device protocols. Translatinon between logical and physical accesses and addresses.

Traditional SCSI Bus

Pronounced 'skuzzy'. Traditional SCSI is a high speed parallel-bus designed for "universal" I/O interfacing. Supports multiple devices from a single SCSI port. Because of high transfer rates, SCSI was the obvious interface choice for server applications. SCSI offered the highest available bandwidth, outof-order command execution, lower CPU utilization, easier handling of large numbers of storage devices, and access to the market's most advanced hard drives.

I/O Module Functions

Recognizes messages from device(s) addressed to it and accepts commands from the CPU. Provides a buffer where the data from memory can be held until it can be transferred to the device. Provides the necessary registers and controls to perform a direct memory transfer (DMA). Physically controls the I/O device. Copies data from its buffer to the device/from the CPU to its buffer. Communicates with CPU.

Direct Memory Access (DMA)

Required conditions for DMA: The I/O interface and memory must be connected. The I/O module must be capable of reading and writing to memory. Conflicts between the CPU and the I/O module must be avoided. Interrupt is required for completion from I/O module.

Storage Interfaces

SATA, PCI Express, SAS, USB

Mother Board

The main circuit board in a computer that contains the central processing unit, the co-processor, device controllers, memory and expansion shots.

Processor Speed

The on and off switching of transistors within the integrated circuits of a computer is managed by a central digital electrical signal called a clock.

Why Serial Connection is Faster for High Rate Transmission? (cont2)

The simple serial bus connection needs only one Data line (Data dent from the sender) and one ACK (acknowledgement) line (ACK sent from the receiver) for one-way communication.

Chip Set

The term chip set refers to a group of chips on motherboard that support the microprocessor by controlling the flow of information between it and other components, such as the memory chips, graphics and sound cards, disk drives, and I/O devices. Various manufacturers produce different types of chip sets, which can significantly affect computer performance, due to the limitations that chip sets may impose on memory size, number of processors, and bus speed.

DMA Procedure

To initiate DMA, the I/O service program from operating system uses programmed I/O (i.e., CPU controlled I/O) to send the following information to I/O module: location of data on I/O device, the starting location of the data in memory, the size of the data to be transferred, direction: read or write. DMA transfer takes place, & upon completion, I/O module sends an interrupt to CPU.

Bus Interconnection

bus can be point-to-point, connecting two specific components single source to single destination. Or it can be a common pathway, a multipoint bus that connects a number of devices, requiring these devices to share the bus. At any one time, only one device may use the bus.

serial ATA (SATA)

is an evolutionary storage interface that has replaced the legacy IDE and PATA. Used widely for personal computers. Uses 7 pin cable for data transfer to connect the storage device to the computers motherboard. Reduced cable-bulk and cost vs PATA. Also faster and more efficient data transfer. Ability to remove or add devices while operating.

Why Serial Connection is Faster for High Rate Transmission? (cont3)

it is much simpler to time the arrival of bits along a single serial path (with near constant delay) than to match up the bits of a parallel data (arriving at different times), so bits can be transmitted at a faster rate with serial connection. For today's high transfer rates, it is quicker and cheaper to design and manufacture faster serial data buses (cables) than to design and build the synchronization circuitry needed for parallel transmission. In addition, the synchronization logic increases power consumption, and thus heating. For serial connection, cables are smaller, which restrict air circulation less, reducing possible hot spots in a computer enclosure. Also, smaller cables are generally more flexible

Bus Clock

like the cpu, bus has a clock that coordinates activities of all attached devices. Bus clock pulse refers to common timing for all attached devices.

Bus Access Control

master-slave approach, peer-to-peer approach.

Bus Data Transfer Rate

measured by data transfer rate = data transfer unit size x clock rate. Can be only increased by increasing bus clock rate, increasing # of bits transmitted per clock cycle, using a more efficient bus protocol.

Bys Types

memory bus, I/O bus, backplane bus. Computers have a hierarchy of buses, so it is not uncommon to have two busses.

PCI

one such I/O bus standard that supports the connection of multiple peripheral devices to CPU and memory. Most desktop and laptop computers and many midrange computers implement some version of PCI bus standard.

Expansion Slots

openings on the motherboard where various boards can be plugged in to add new capabilities to a comp. Additional memory, video cards, sound cards etc.

USB Hubs

provide multiple connection points for i/o devices.

Power Lines

provide the electrical power necessary.

PCIe

serial connectors are physically smaller due to fewer wires. serial channels can operate at higher speed and can allow attached devices to operate a different fractions of the maximum speed.

The Bus

system bus is a communication channel that connects CPU, primary storage and peripheral devices such as secondary storage, network and video controllers. Behaves like a highway that is used by multiple devices. Consists of multiple lines, allowing parallel movement of bits. Lines are printed on a curciut board called a mother board.

Bus Protocol

the bus protocol is important. Documented agreement for communication. For example, a particular control line on a bus might be defined as a line that determines if the bus is to be used for memory read or memory write

Bus Clock Rate

the frequency of busl clock pulses. Measured in MHz-million cycles per second. Or GHz-billion cycles per second. bus cycle time = 1/bus clock rate.

More About Serial and Parallel Connections

the point-to-point serial link allows more than one pair of devices to communicate with each other at the same time.

Bus Clock Cycle

time interval from one clock pulse to the next. Is equal to one transfer time of command information, data, or both. Clock is a common timing reference that coordinates the activities of sending and receiving devices.

IEEE 1394

two data transfer modes. Asynchronous mode (ensures data is delivered reliably) and Isochronous mode (transfers allow guaranteed bandwidth but do not provide for error correction or retransmission.

External Ports for Video and Audio

VGA, DVI, Display, HDMI and Audio ports

External Ports

a connector at the end of a bus into which a peripheral device can be plugged. Ports connect to the motherboard itself. Allow for the movement of data to and from devices external to the computer.

Parallel ATA (PATA)

An older IDE cabling method that uses a 40-pin flat or round data cable or an 80-conductor cable and a 40-pin IDE connector. See also serial ATA.

Parallel Port (external port)

An interface between computer and peripheral devices like printers with parallel communication. Use at least 8 data lines, which are energized simultaneously to transmit data. Before the wide use of USB ports, a 25-pin female parallel port (DB-25) on the computer was commonly used to connect the printers.

PCI-X

Address and data bus lines are shared (one PCI device sends immediately after the other in successive bus cycles.) Parallel channels are relatively slow and require all attached devices to have the same physical interface and operate at the same clock speed.

Address Lines

Address lines indicate the location (e.g., in memory) that the data should be either read from or written to.

USB Logical Connections

Although the physical structure of a USB system is a tiered star, it is logically a star network. All nodes have to communicate with each other via the single central node (the host).

Bus Hierarchy

CPU data bus, cache bus, front-side bus, memory bus, i/o and backplane bus.

Components of a Motherboard

CPU, Power Connector, Memory, North Bridge, South Bridge, Battery, IDE or SATA, PCI Slots, VGA - Monitor, Serial Port, USB, Moshe and Keyboard input.

Backplane Buses for Attaching Hardware Devices

Computer systems augment their main bus with dedicated I/O buses using these expansion slots to connects I/O peripheral components and the CPU: ISA, PCI, PCI-X, PCI-express

Control Lines

Control lines indicate which device has permission to use the bus and for what purpose (e.g., reading or writing from memory or from an input/output [I/O] device). Control lines also transfer acknowledgments for bus requests, interrupts, and clock synchronization signals.

Storage Interfaces: IDE, EIDE, ATA

IDE, EIED, and ATA are standard interfaces for connecting magnetic and optical storage devices such as hard disks and CD/DVD-ROM drives.IDE (Integrated Drive Electronics) EIDE (Enhanced IDE) ATA (Advanced Technology Attachment). Most ATA, IDE, and EIDE systems share the main system bus with the processor and memory, so the movement of data to and from the disk is also dependent on the speed of the system bus

Input/Output

For many business programs, e-commerce applications (like web services), and nearly all multimedia applications, the processing speed or program execution is determined primarily by the ability of I/O operations to stay ahead of the processor.

Why Serial Bus is Faster for High Data Rate Transmission? (cont)

For transmission at high data rate, synchronization is not easy for parallel connection. However, there is a slight difference in time delay on different lines, know as skew, when data transfers over the parallel bus. Thus, the data transfer rate, and thus the clock speed of the parallel bus, is also limited by the requirement that the data must not change faster than the maximum skew time. Both the problems of electrical interference and skew can cause data corruption.

Summary

How the CPU uses the system bus and device controllers to communicate with storage and input/output devices. Hardware and software techniques for improving data efficiency, and thus, overall computer system performance.

I/O Bus Architecture

I/O bus architecture consists of an I/O device, I/O device controller (I/O module), system bus, and a device driver. Common interface buses: SATA, SCSI, IEEE, USB

Serial Attached SCSI (SAS) Bus

Serial Attached SCSI (SAS) is a replacement for parallel SCSI for much higher speed data transfers. SAS 4.0 (22.5Gbps) in 2018. Like SATA, SAS is a point-to-point serial bus, which is the modern version of SCSI and is widely used in servers. SAS is an enterprise-level interface used to connect large numbers of storage devices. SAS can handle many storage devices (hundreds or thousands) on a single host interface. But keep in mind that all those devices share a single pipe to the host adapter; the aggregate bandwidth is still limited to 22.5 Gbps with SAS 4.0.

Master-slave Approach

Some devices that attach to a bus are active and can initiate bus transfers, whereas others are passive and wait for requests. The active ones are called masters (or bus masters). Bus Master controls all bus transfers. Simple but relatively inefficient b/c the bus master is a bottleneck. CPU is usually acting as a master.

Universal Serial Bus (USB)

Standard for computer ports that support data transfer rates of up to 12 million bits per second. Flash memory provides robust, high-density, low size, non-volatile storage at low prices, and USB technology allows you to connect almost any modern digital device to a computer - or even to connect two digital devices together without a host computer (e.g., a camera and a printer).

I/O Modules

The I/O module is responsible for the control of one or more I/O devices and for the exchange of data between those devices and CPU registers. Must have an interface internal to cpu/memory and external to device. Receives commands from the CPU and provides control of i/o devices as to execute those commands. the I/O module also responses to interrupt requests from I/O device and pass them to the CPU to process those requests. I/O modules that control a single type of device (I/O unit) are often called device controllers ( or I/O controllers) such as disk controller.

FSB (front side bus)

The connection between the CPU to the motherboard components. Considered the speed of the motherboard.

serial port (external port)

Transfer data by sending a series of bits across one or two data lines (data and ACK). Even though the communication in PS/2 and USB is serial, technically, the term Serial Port is used to refer the interface that is compliant to RS-232 standard. DE-9 is the main port for RS-232 serial communication, a 9-pin male port used on older computers. A DE-9 port is also called as a COM port and allows full duplex serial communication between the computer and it's peripheral.

Data Transmission Over Bus

Typical bus transactions include sending an address (for a read or write), transferring data from memory to a register (a memory read), and transferring data to the memory from a register (a memory write). Buses are used for i/o reads and writes from peripheral devices. Each type of transfer occurs within the bus cycle, the time between two ticks of the bus clock.

External Ports: USB, FireWire, eSATA

USB (universal serial bus) port: a multi-purpose I/O port used by many different devices, including printers, mice, keyboards, scanners, external hard drives, and flash drives.FireWire port: also called IEEE 1394 port, used for high speed multimedia devices such as digital camcorders. External SATA (eSATA) port: used by an external hard drive using the eSATA interface. eSATA is faster than fireWire.

Universal Serial Bus (USB) (cont)

USB is a popular external bus that supports plug-and-play installation (the ability to configure devices automatically) as well as hot plugging (the ability to add and remove devices while the computer is running).

FireWire Daisy-Chain

Up to 16 FireWire devices can be connected to a single IEEE1394 port through daisychaining. By using hubs, up to 63 devices can be connected to a single IEEE1394 port.

Speed Up Processor Operations

accessing L2 cache and motherboard components was a bottleneck in older systems because the CPU used the same bus to communicate with RAM and other motherboard components as it did with L2 and motherboard cache. The solution is DIB (dual independent bus). With DIB, two buses are used: a back side bus and front side bus.

Backplane Bus

an electrical connector that joins several electrical circuits together. The backplane connectors are parallel to each other in order to link each pin to its relative pin on each connector, forming a complete computer bus. The backplane is a printed circuit board containing connections (slots) for expansion circuit boards (or interface cards) and allows for communication between all connected boards. Built into the chassis of the machine and connects the processor, I/O devices and the memory.

Peer-to-peer Approach

any device can temp become a bus master to control the bus. Requires a protocol for "passing around" the bus master role and a prioritization scheme for competing requests to be bus master

Memory Bus

connects only the CPU and memory. Processor-memory buses are short, high speed buses that are closely matched to the memory system on the machine to maximize bandwidth and are usually design specific.

BSB (back side bus)

connects the CPU to the L2 cache.

4 kinds of line

data, address, control, and power.

Peripheral devices

devices other than the CPU and primary storage.

word size

expressed in terms of bits. Increasing size usually increases CPU efficiency, up to a point.

USB Physical Connections

host controlled. Does not support a multi-master arrangement. A USB hub may be connected directly to a peripheral, or to several peripherals, or to another USB hub.