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Friday, August 29, 2008

expansion slots

The expansion slots allow the computer system to communicate with the outside world. The success of the IBM compatible has been mainly due to its ability to change, and add, new features by doing nothing more than just fitting them into these slots.

The original IBM PC-AT ran its system with a clock speed of 8MHz. Manufacturers, using the PC-AT design for their computers, called "clones", moved in the direction of compatibility with the PC-AT. This meant that any board plugged into the expansion slot of the "clones" could only run at speeds of 8MHz to ensure this compatibility.


As the technology of the clones evolved, with microprocessor speeds of 10,12, and then 16 MHz being reached, the 'plug-in' speed remained at 8MHz because of the need to ensure compatibility with the PC-AT. This resulted in delays as the microprocessor had to wait around for the rest of the system to catch up.The main problem was that the RAM memory of the computer was in the form of plug-in cards.

A way around the problem was for designers to move the RAM (Random Access Memory) off plug-in cards onto the motherboard with the processor. They also gave RAM its own bus to the processor, called the local bus. This now allowed RAM to run at the same speed as the processor. It being many times faster than cards using the original 'Industrial Standard Architecture' (ISA) IBM PC-AT 8MHz system. Effectively Local Bus means that memory is addressed directly by the CPU.

As processor speeds increased the next bottleneck was the presenting of information on the monitor screen. To overcome this, video data was also placed on the local bus away from the 16 bit, 8MHz ISA bus. To allow for the need of users wanting to upgrade to new video standards, a local bus connector was provided allowing the plugging in of common video controller boards, called the 'Video Local Bus' (VLB) cards.

The two most popular designs is the older, VESA(Video Electronics Standard Association), or VLB local bus and the newer PCI(Peripheral Component Interconnect) Local Bus found in newer Pentiums. Both offer 32-bit data transfer rates at up to 33MHz although the PCI has the edge in speed by reducing processor wait state writes to the video memory. PCI also has the advantage of plug-and-play ability as used with Windows 95. All you need do is to install a plug-and-play graphics card and Windows 95 will configure it for best operation with your system. Consequently, most modern systems now use PCI Local Bus which is incompatible with the VESA LB.

VESA LB, or VLB, still have a standard ISA bus slot as an extension of its bus connector. This allows a PC-AT board to be plugged into a standard ISA connector, or the particular connector on the VESA LB slot. A VESA LB board, however, can only be connected into appropriate slot of the combination board connector. The provision allows for the connection of older ISA or VLB boards to be connected in the same expansion slot.

The PCI system has a separate set of PCI and a few standard ISA connectors, boards are not interchangeable between the two connectors.

In the latest systems the disc data is also being moved to the local bus to avoid the slow 8MHz PC-AT bus.

The PCI bus is very fast and is now the standard bus used with new video boards. Running at clock speed of 33 Mhz, the PCI local bus uses 32-bit data bus that supports add-in cards and peripheral components at 132 MB/sec. bandwidth. This compares with the ISA data transfer rate of 5MB/sec. There is a 64-bit data transfer extention to basic PCI which adds a futher 60 pins to the 120 available on the 32-bit card. This doubles the data transfer speed to 264MB per second.

The older 'VESA bus video card' can not be used with the newer PCI bus because the two are incompatible. The 486 processor motherboard used the VESA LB as did some of the older Pentium boards. So when upgrading be aware that you need to check if the motherboard uses VESA or PCI local bus. As all new systems now use PCI Local Bus, you will eventually have purchase a video card that uses PCI LB.


Expansion Slots
Expansion Slot Openings
Expansion slots openings are located on the back of the computer.They look like the ones shown in the figure above.They provide access to the AGP,PCIe,PCIand ISA expansions slots one the motherboard.To use this expansion slot opening,a person would need an expansion card like the sound blaster live card as shpwn below,which is actually two cards Sound Blaster Card
The top card plugs into a PCI slot, while the bottom card sends and receives its data through the larger card via the connected cable. The smaller card simply needs an empty expansion slot opening on the back of the case to mount to. The expansion slot opening you clicked on would be perfect for the bottom card.



Tuesday, August 26, 2008

FIREWIRE

FireWire is Apple Computer's version of a standard,IEEE 1934, High Performance Serial Bus, for connecting devices to your personal computer. FireWire provides a single plug-and-socket connection on which up to 63 devices can be attached with data transfer speeds up to 400 Mbps (megabits per second). The standard describes a serial bus or pathway between one or more peripheral devices and your computer's microprocessor. Many peripheral devices now come equipped to meet IEEE 1394. FireWire and other IEEE 1394 implementations provide:
  • A simple common plug-in serial connector on the back of your computer and on many different types of peripheral devices
  • A thin serial cable rather than the thicker parallel cable you now use to your printer, for example
  • A very high-speed rate of data transfer that will accommodate multimedia applications (100 and 200 megabits per second today; with much higher rates later)
  • Hot-plug and plug and play capability without disrupting your computer
  • The ability to chain devices together in a number of different ways without terminators or complicated set-up requirements

In time, IEEE 1394 implementations are expected to replace and consolidate today's serial and parallel interfaces, including Centronics parallel,rs 232c, and Small Computer System Interface (scsi). The first products to be introduced with FireWire include digital cameras, digital video disks (dvds), digital video tapes, digital camcorders, and music systems. Because IEEE 1394 is a peer to peer interface, one camcorder can dub to another without being plugged into a computer. With a computer equipped with the socket and bus capability, any device (for example, a video camera) can be plugged in while the computer is running.

Briefly How It Works

There are two levels of interface in IEEE 1394, one for the black plane bus within the computer and another for the point-to-point interface between device and computer on the serial cable. A simple bridge connects the two environments. The backplane bus supports 12.5, 25, or 50 megabits per second data transfer. The cable interface supports 100, 200, or 400 megabits per second. Each of these interfaces can handle any of the possible data rates and change from one to another as needed.

The serial bus functions as though devices were in slots within the computer sharing a common memory space. A 64-bit device address allows a great deal of flexibility in configuring devices in chains and trees from a single socket.

IEEE 1394 provides two types of data transfer: asynchronous and synchronous . Asynchronous is for traditional load-and-store applications where data transfer can be initiated and an application interrupted as a given length of data arrives in a buffer. Isochronous data transfer ensures that data flows at a pre-set rate so that an application can handle it in a timed way. For multimedia applications, this kind of data transfer reduces the need for buffering and helps ensure a continuous presentation for the viewer.

The 1394 standard requires that a device be within 4.5 meters of the bus socket. Up to 16 devices can be connected in a single chain, each with the 4.5 meter maximum (before signal attenuation begins to occur) so theoretically you could have a device as far away as 72 meters from the computer.

Another new approach to connecting devices, the Universal Serial Bus (usb), provides the same "hot plug" capability as the 1394 standard. It's a less expensive technology but data transfer is limited to 12 Mbps (million bits per second). Small Computer System Interface offers a high data transfer rate (up to 40 megabytes per second) but requires address preassignment and a device terminator on the last device in a chain. FireWire can work with the latest internal computer bus standard, Peripheral Component Interconnect (pci), but higher data transfer rates may require special design considerations to minimize undesired buffering for transfer rate mismatches.

Hard disk controller

Hard disk controller
Generally abbreviated as HDC, the hard disk controller is the interface that allows the computer to interface with a hard disk drive. Today, hard disk drives have the controller built on to them.

Early disk controllers were identified by their storage methods and data encoding. They were typically implemented on a separate controller card. Modified frequency modulation (MFM) controllers were the most common type in small computers, used for both floppy disk and hard disk drives. Run length limited (RLL) controllers used data compression to increase storage capacity by about 50%. Priam created a proprietary storage algorithm that could double the disk storage. Shugart Associates Systems Interface (SASI) was a predecessor to SCSI.

Main article: Hard drive

Modern disk controllers are integrated into the disk drive. For example, disks called "SCSI disks" have built-in SCSI controllers. In the past, before most SCSI controller functionality was implemented in a single chip, separate SCSI controllers interfaced disks to the SCSI bus.

The most common types of interfaces provided nowadays by a disk controllers are ATA (IDE) and Serial ATA for home use. High-end disks use SCSI, Fibre Channel or Serial Attached SCSI.

Disk controller versus host adapter

The correct term for the components that allows a computer to talk to a peripheral bus is host adapter or host bus adapter (HBA). On other hand, a disk controller allows a disk to talk to the same bus. Those two are often confused, especially in PC world. In fact signals read by a disk read-and-write head are converted by a disk controller, then transmitted over peripheral bus, then converted again by host adapter into motherboard's bus suitable format and then read by CPU.

Sometimes there may be yet another controller between a host adapter and a disk controller - a disk array controller that allows hardware RAID to be formed. Sometimes it may be even physically integrated with an HBA, but it performs different functions.

Monday, August 25, 2008

INTEGRATES DRIVE ELECTRONICS

IDE

  1. Short for Integrated Drive Electronics or IBM Disc Electronics, IDE is more commonly known as ATA and is a standard interface for IBM compatible hard drives. IDE is different from the Small Computer Systems Interface (SCSI) and Enhanced Small Device Interface (ESDI) because its controllers are on each drive, meaning the drive can connect directly to the motherboard or controller. IDE and its updated successor, Enhanced IDE (EIDE), are the most common drive interfaces found in IBM compatible computers today. Below is a picture of the actual IDE connector and cable.

    40-pin IDE connector and cable

    Additional information about IDE and other computer interfaces can be found here.
  2. Short for Integrated Development Environment, IDE also sometimes referred to as IDLE, IDEs are visual tools that allow programmers to develop programs better. Commonly, an IDE may have a compiler, debugger, text editor, and other integrated tools. Smalltalk was the first programming language to have a first true IDE.

INTEL HUB ARCHITECTURE

Intel Hub Architecture

Intel's architecture for the 8xx family of chipsets, starting with the 820. It uses a memory controller hub (MCH) that is connected to an I/O controller hub (ICH) via a 266 MB/sec bus. The MCH chip supports memory and AGP, while the ICH chip provides connectivity for PCI, USB, sound, IDE hard disks and LAN.

Because of the high-speed channel between the sections, the Intel Hub Architecture (IHA) is much faster than the earlier Northbridge/Southbridge design, which hooked all low-speed ports to the PCI bus. The IHA also optimizes data transfer based on data type. See Northbridge and Intel chipsets.



Intel's Chipset Architecture
Intel introduced its hub architecture starting with the 820 chipset, which divides control between a memory controller chip (MCH) and an I/O controller chip (ICH). This is an illustration of the 850.

Industry Standard Architecture (ISA) Bus

Industry Standard Architecture (ISA) Bus

The most common bus in the PC world, ISA stands for Industry Standard Architecture, and unlike many uses of the word "standard", in this case it actually fits. The ISA bus is still a mainstay in even the newest computers, despite the fact that it is largely unchanged since it was expanded to 16 bits in 1984! The ISA bus eventually became a bottleneck to performance and was augmented with additional high-speed buses, but ISA persists because of the truly enormous base of existing peripherals using the standard. Also, there are still many devices for which the ISA's speed is more than sufficient, and will be for some time to come (standard modems being an example).

(As a side note, after 17 years it appears that ISA may finally be going the way of the dodo. Market leaders Intel and Microsoft want to move the industry away from the use of the ISA bus in new machines. My personal prediction is that they will succeed in this effort, but that it will take at least five years to do it fully. There are few standards in the PC world as pervasive as ISA, and the hundreds of millions of existing ISA cards will ensure that ISA sticks around for some time.)

ISA is a type of bus used in PCs for adding expansion cards. For example, an ISA slot may be used to add a video card, a network card, or an extra serial port. The original 8-bit version of PCI uses a 62 pin connection and supports clock speeds of 8 and 33 MHz. 16-bit PCI uses 98 pins and supports the same clock speeds.

The original 8-bit version of ISA was introduced in 1981 but the technology did not become widely used until 1984, when the 16-bit version was released. Two competing technologies -- MCA and VLB -- were also used by some manufacturers, but ISA remained the most common expansion bus for most of the 1980s and 1990s. However, by the end of the twentieth century, ISA ports were beginning to be replaced by faster PCI and AGP slots. Today, most computers only support PCI and AGP expansion cards.

The choices made in defining the main characteristics of the ISA bus--its width and speed--can be seen by looking at the processors with which it was paired on early machines. The original ISA bus on the IBM PC was 8 bits wide, reflecting the 8 bit data width of the Intel 8088 processor's system bus, and ran at 4.77 MHz, again, the speed of the first 8088s. In 1984 the IBM AT was introduced using the Intel 80286; at this time the bus was doubled to 16 bits (the 80286's data bus width) and increased to 8 MHz (the maximum speed of the original AT, which came in 6 MHz and 8 MHz versions).

Later, the AT processors of course got faster, and eventually data buses got wider, but by this time the desire for compatibility with existing devices led manufacturers to resist change to the standard, and it has remained pretty much identical since that time. The ISA bus provides reasonable throughput for low-bandwidth devices and virtually assures compatibility with almost every PC on the market.

Many expansion cards, even modern ones, are still only 8-bit cards (you can tell by looking at the edge connector on the card; 8-bit cards use only the first part of the ISA slot, while 16-bit cards use both parts). Generally, these are cards for which the lower performance of the ISA bus is not a concern. However, access to IRQs 9 through 15 is provided through wires in the 16-bit portion of the bus slots. This is why most modems, for example, cannot be set to the higher-number IRQs. IRQs cannot be shared among ISA devices.


Industry Standard Architecture (in practice almost always shortened to ISA) was a computer bus standard for IBM compatible computers.

History

ISA originated as an 8-bit system in the IBM PC in 1981, and was extended in 1983 as the XT bus architecture. The newer 16-bit standard, the IBM AT bus, was introduced in 1984. In 1988, the Gang of Nine IBM PC compatible manufacturers put forth the 32-bit EISA standard and in the process retroactively renamed the AT bus to be "ISA" to avoid infringing IBM's trademark on its PC/AT computer.

Designed to connect peripheral cards to the motherboard, ISA allows for bus mastering although only the first 16 MiB of main memory is available for direct access. The 8-bit bus ran at 4.77 MHz, while the 16-bit bus operated at 6 or 8 MHz. IBM RT/PC also used the 16-bit bus. It was also available on some non-IBM compatible machines such as the short-lived AT&T Hobbit and later PowerPC based BeBox.

In 1987, IBM moved to replace the AT bus with their proprietary Micro Channel Architecture (MCA) in an effort to regain control of the PC architecture, and the PC market. The system was far more advanced than the AT bus, and computer manufacturers responded with the Extended Industry Standard Architecture (EISA) and later, the VESA Local Bus (VLB). In fact, VLB used some parts originally intended for MCA due to the fact that component manufacturers already had the ability to manufacture it. Both were compatible expansions of the AT bus.

Users of ISA-based machines had to know special information about the hardware they were adding to the system. While a handful of devices were essentially "plug-n-play," this was rare. Users frequently had to configure several parameters when adding a new device, such as the IRQ line, I/O address, or DMA channel. MCA had done away with this complication, and PCI actually incorporated many of the ideas first explored with MCA (though it was more directly descended from EISA).

This trouble with configuration eventually led to the creation of ISA PnP, a plug-n-play system that used a combination of modifications to hardware, the system BIOS, and operating system software to automatically manage the nitty-gritty details. In reality, ISA PnP turned out to be a major headache much of the time, and didn't become well-supported until the architecture was in its final days. This was a major contributor to the use of the phrase "plug-n-pray."

PCI slots were the first physically-incompatible expansion ports to directly squeeze ISA off of the motherboard. At first, motherboards were largely ISA, including a few PCI slots. By the mid-1990s, the two slot types were roughly balanced, and ISA slots soon were in the minority of consumer systems. Microsoft's PC 97 specification recommended that ISA slots be removed entirely, though the system architecture still required ISA to be present in some vestigial way internally to handle the floppy drive, serial ports, etc. ISA slots remained for a few more years, and it was even possible to see systems with an Accelerated Graphics Port (AGP) sitting near the central processing unit, an array of PCI slots, and one or two ISA slots near the end.

It is also notable that PCI slots are "rotated" compared to their ISA counterparts—PCI cards were essentially inserted "upside-down," allowing ISA and PCI connectors to squeeze together on the motherboard. Only one of the two connectors can be used in each slot at a time, but this allowed for greater flexibility.

8-bit ISA (XT bus architecture)

The XT bus architecture is an eight-bit ISA bus used by Intel 8086 and Intel 8088 systems in the IBM PC and IBM PC XT in the 1980s.

An 8-bit ISA (XT-bus) mouse adapter

An 8-bit ISA (XT-bus) mouse adapter

The XT bus has four DMA channels, of which three are brought out to the expansion slots. Of these three, two are normally allocated to machine functions:

DMA channel Expansion Standard function
0 No Dynamic RAM refresh
1 Yes Add-on cards
2 Yes Floppy disk controller
3 Yes Hard disk controller

The XT bus architecture has single Intel 8259 PIC and eight interrupt lines.

16-bit ISA (AT bus architecture)

The AT bus architecture is an 16-bit version of the ISA bus first in the IBM PC/AT.

Technical data

8 bit ISA or XT bus architecture

XT_Bus_pins.png
Bus width 8-bit
Compatible with 8 bit ISA
Pins 62
Vcc +5 V, -5 V, +12 V, -12 V
Clock 4.7727266 MHz

16 bit ISA

ISA_Bus_pins.png
Bus width 16-bit
Compatible with 8 bit ISA, 16 bit ISA
Pins 98
Vcc +5 V, -5 V, +12 V, -12 V
Clock 8.333333 MHz
Capacity
3,97 MiB/s (pio)
2,65 MiB/s (dma)

Note: The ISA bus speed is actually synchronous with the CPU clock speed, resulting in many differing clock speeds, due to the many different speed machines produced by the many 'IBM clone' manufacturers. This led to problems by the late 1980s, where certain ISA cards would suffer compatibility problems and malfunctions when fitted to machines with bus speeds as high as 16MHz. This problem was solved with later, highly integrated chipsets that (generally) standardized the 16-bit ISA bus to 8MHz; this was achieved by under-clocking the CPU to 8MHz only during ISA bus accesses.

Current use

Apart from specialized industrial use, ISA is all but gone today. Even where present, system manufacturers often shield customers from the term "ISA bus", referring to it instead as the "legacy bus" (see legacy system). The PC/104 bus, used in industrial and embedded applications, is a derivative of the ISA bus, utilizing the same signal lines with different connectors. The LPC bus has replaced the ISA bus as the connection to the legacy I/O devices on recent motherboards; while physically quite different, LPC looks just like ISA to software, so that the peculiarities of ISA such as the 16 MiB DMA limit are likely to stick around for a while.

Starting with Windows Vista, Microsoft is phasing out support for ISA cards in Windows. Vista still supports ISA-PnP for the time being, although it's not enabled by default.

Standardization

IEEE started a standardization of the ISA bus in 1985, called the P996 specification. However, despite even books being published on the P996 specification, it has never officially gotten past draft status.