The developers of computers, motherboards are based on
180386/486 microprocessors, have to use separate bus for memory and
I / O devices, allowing for maximum use of opportunities
RAM, as it is in this case, the memory can work with
best for her speed. Nevertheless, under this approach, the system can not
to ensure adequate performance, as well as devices that are connected
through expansion connectors, can not reach the speed of exchange, comparable to
Processor. Mainly concerned with controllers and drives
video adapter. To resolve this problem have been used so
called the local (local) bus, which directly connect processor
controllers and peripherals.
The first IBM PC-compatible computers with local tires were not, of course,
standardized. One of the leading manufacturers of personal computers,
videopodsistemu first implemented with a local bus, a company NEC
Technologies. Even in 1991, the company submitted its original formulation
Image Video.
Tires VL-bus and PCI
Recently, there have been two local tire recognized by industry: VL-bus
(or VLB), the proposed association VESA (Video Electronics Standards
Association), and PCI (Peripheral Component Interconnect), developed by
Intel. Both of these tires are, generally speaking, for the same - to
increase in computer performance, thereby allowing the peripheral devices,
as adapters and controllers drives, with a clock speed of up to 33
MHz and higher. Both types of connectors used tires MSA. At the same time, however, their similarities
and ends, as desired objective is achieved by different means.
If the VL-bus is, in fact, increased tire processor (remember the bus IBM
PC / XT), a PCI to their organization over the system tends to tire, such as
EISA, and represents a completely new development. Strictly speaking, PCI
belongs to a class of so-called mezzanine-tire, that is, tires, "extensions"
as a local bus between the processor and PCI is very special
chip consent "bridge" (bridge).
As the VL-bus continued to tire processor without intermediate buffers, it Schem
Implementation is cheaper and simpler. The first specification VESA, in
alia, that the tire, which is a local 32-bit
bus system microprocessor, can connect up to three peripheral
devices. Some manufacturers, however, believe that to achieve sustainable
the three devices at high frequencies at all impossible, and set at
their pay only 2 slots. Limiting the number of devices connected with the fact that
electrical load capacity signal from any processor
very small.
As the devices connected to the VL-bus, currently serve
controllers drives, video adapters, and network card. VL-bus design
looks like a short connector type MSA (112 contacts), fixed,
for example, next to the ISA expansion connectors, or EISA. In this line 32
used for data transfer and 30 - to transfer the addresses. Top
data transmission speed of the bus VL-bus can theoretically be about 130
MB / sec. It is noteworthy that the VL-bus arbitrator does not tire. Fortunately,
Most plug it is a "passive", ie not themselves
initiate data transfer. Nevertheless, to avoid possible conflicts between
connected to the bus devices in the specifications are "managers"
(master) and "managed" (slave) adapters. For the "Governing" devices on
motherboards usually defined its "masternye" slots. According to the
Developers such as "control" device can carry out arbitration
tire.
When you see Pentium Processor Association VESA begun work on new
Standard VL-bus (version 2). It provides, inter alia, the use of
64-bit data bus and an increase in the number of connectors expansion
(presumably three slots at 40 MHz and two at 50 MHz). Expected speed
transfer theory should increase to 400 megabytes per second. Note that the
Time bus VL-bus is a relatively inexpensive addition to
Computer-based 486-x processors tire ISA, and with
backward compatibility.
Specifications for PCI has several advantages over the basic version
VL-bus. For example, you can use the PCI regardless of the type of processor.
Special controller cares about the division of local control signals
tire processor and PCI-bus and furthermore Arbitration for implementing PCI. It is
so the tire can be used in other computer platforms.
It should be noted that flexibility and speed of the bus and require large
hardware costs than the VL-bus. However, PCI bus has become a practical
standard for systems based on Pentium and no less successfully used in 486-x
computers.
In accordance with the specification to the PCI bus can connect up to 10 devices.
This, however, does not use the same number of expansion connectors --
restriction applies to the total number of components, including those located at
the motherboard. Since each PCI expansion card can be shared among
two peripheral devices, it reduces the total number of installed
connectors. Unlike the VL-bus PCI bus operates on a fixed clock
frequency of 33 MHz and provides supply voltage controllers as 5, so
and 3.3 V, as well as their auto mode (plug and play --
"includes labor). Note that, for example, PCI-cards that are designed to
5 The voltage can be inserted in the appropriate slots, which
constructively different from the slots for voltage 3.3 V.
However, there are the so-called universal PCI-controllers, who work in
any of the slots. Bus PCI can use 124-pin (32-bit) or
188-pin connector (64-bit data transfer), while in theory
exchange rate is respectively 132 and 264 Mbaita / s
Specifications PCI 2.1 per microprocessor Pentium (100 MHz) defines
work with a frequency of 33-66 MHz and the exchange rate to 520 MB / sec. At the systemic
motherboards usually not set more than three or four connectors PCI.
Separately, I would like to say about the so-called razdelyaemy (shared) slots
ISA / PCI. Since slots for PCI bus terminals are located in parallel
system bus, the term of the board because of her limited size sufficient
difficult to accommodate the required number of both. It is therefore not that
producing and using shared or shared configuration. In this case,
one PCI slot is located so close to the connector system bus that
You can only use one of them, that is connected or ISA-, or
PCI-device, but, of course, for the connector.
Generally speaking, many manufacturers of motherboards often include in their
products varied combination of systemic and local bus from the ISA plus VL-bus
for relatively low-cost systems to the EISA plus PCI systems for high-ypov class.
Often found a combination of ISA EISA plus plus VL-bus ISA plus plus EISA and PCI
even all four tires at the same time providing some flexibility when you
Bor adapters especially given the high prices of products for tires and EISA
PC. Nonetheless, "war" local tire clear pobedu won PCI.
The standard PCMCIA
The devices that match the first version of the standard PCMCIA, conceived as
Alternative energy and heavy on both floppy disks in
portable computers. Recall that the "mysterious" abbreviation means PCMCIA
but a Personal Computer Memory Card International Association.
Incidentally, the adoption of the Association specification was immediately supported by such
companies as IBM, AT & T, Intel, NCR and Toshiba. Today the standard
supported by nearly 300 manufacturers. PCMCIA-sized device with a normal
Credit card is an alternative to conventional card expansion,
connected to the system bus. Today the standard modules available
memory, modems and fax modems, SCSI-adapters, network cards, sound cards,
vinchestery etc. Especially popular PCMCIA-card flash memory,
who do not lose information when turned off power, have a high
speed and can be used as a hard drive without moving
parts.
By the way, and for desktop computers has been developed Adapters
PCMCIA-devices. A PCMCIA adapter card expansion meant that
usually inserted into the slot system bus and connects to the PCMCIA connector
ribbon cable connector. Sam PCMCIA slot is located in a standard compartment with
the form factor of 3.5 or 5.25 inches.
The first version of the standard PCMCIA (release 1.0) was introduced in August 1990 and
supported all types of memory, excluding the dynamic memory DRAM. Thus,
in the specification included: static memory SRAM; Pseudo memory
PSRAM; constant (mask) memory ROM; one-time programmable constant
memory PROM (or OTPROM - One-Time Programmable ROM); erasable ultraviolet
reprogrammable memory of UV-EPROM (Ultraviolet Erasable PROM); electrically
erasable reprogrammable memory EEPROM (Electrically Erasable PROM) and
Flash memory (Hash). Work Association PCMCIA over the same specification
was in close contact with the organization JEIDA (Japan Electronic Industry
Development Association) in Japan. Therefore, the standard is often called PCMCIA / JEIDA.
Already in September 1991 a second version of specifications (release 2.0),
which included new features such as support for devices
I / O, an additional service to the flash memory. Support modules
double-voltage (5 and 3) and the so-called XIP mechanism
(eXecute-In-Place). Note that XIP-mechanism providing room to start programs
directly in the space of PCMCIA-memory, thus saving system
computer memory.
To be sure, along with version 2.0 Association PCMCIA developed a new
specification SSIS (Socket Services Interface Specification), which
establishes a standard set of system calls to work with PCMCIA-modules.
SSIS made in the form of BIOS, which allows you to save the independence of
hardware, but to ensure that software compatibility. First
SSIS version was adopted PCMCIA Association in August 1991, but after a month
there is already slightly modified version of SSIS - release 1.01. In the last
SSIS versions have been improved, some previously defined functions and a
support the protected-mode processors. A higher level of program
operations (the so-called Card Services) to the PCMCIA-module was offered only in
early 1992.
The new version allows specification called PCMCIA-ins just a PC Card (s).
So, the PCMCIA standard for communication between the PC Card and the device
(adapter or port) the computer determines the 68-pin machine
connector. There are 16 bits of data and 26 bits of address that
able to directly address 64 MB of memory. Although some discharge
Contacts are intended to signal required when dealing with memory, the same
Contact can be used for other signals at work
I / O devices. Of course, before this happens so-called
reconfiguration of the findings. For example, a contact to signal RDY / BSY (ready / busy)
necessary when dealing with certain types of memory that can be used to
signal IREQ (interrupt request).
On the side of the module PC Card is a connector-socket (female), and on the side
computer - a connector-plug (male). In addition, the standard defines three
various length-contact connector plugs. This solution is easy to explain.
Because the connection and disconnection PC Card can occur when running
computer (so-called hot), then for the first module
supply voltage power supply, but then the voltage signal lines,
contacts met over long. It is clear that if the
PCMCIA-module, everything happens in reverse order. The second version of the specification
PCMCIA defines only three types of dimensions for PC Card (Type I, Type
II and Type III), they should be added and a fourth - Type IV. The first two
Type limit the size of PC Card to 54 mm (2.12 inches) in width and 85.6 mm (3.37
inches) in length. PCMCIA-ins appropriate size Type I, should have
thickness of 3.3 mm, and the related Type II - 5,0 mm in the middle and 3.3 mm at the edges.
This provides a "geometric" compatible PC Card first and second types.
PC Card III tournaments are 10.5 mm thick and, of course, unfit for
use the slots for modules tournaments I and II (see fig. 27). For the third kind
modules are required so-called double-height slots. Note, however, that
Toure III module thickness at the edges is also equal to 3.3 mm. These modules
designed to accommodate 1.3-inch hard drive.
Additions to the second version of the standard PCMCIA to extend the length of
modules of the size of Type I and II, up to 5.73 inches. This construction
especially important for modules modems (fax modem), which, as you know,
must be installed in the connector type RJ-11.
In addition to standard PCMCIA dimensions requires placement of switch
protection records, internal power supplies, name of manufacturer, if
any. To be sure, "teplolyubivye" PC Cards should be fine
operate in temperatures from 0 to 55 degrees Celsius.