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PC/104 (or PC104) is an embedded computer standard
Standardization

Standardization is the process of developing and agreeing upon Standard . A standard is a document that establishes uniform engineering or technical specifications, criteria, methods, processes, or practices....
 controlled by the which defines both a form factor
Form factor

Form factor may refer to:* Form factor or emissivity, the proportion of energy transmitted by that object which can be transferred to another object...
 and computer bus
Computer bus

In computer architecture, a bus is a subsystem that transfers data between computer components inside a computer or between computers. Each bus defines its set of connectors to physically plug devices, cards or cables together....
. PC/104 is intended for specialized embedded computing environments where applications depend on reliable data acquisition
Data acquisition

Data acquisition is the sampling of the real world to generate data that can be manipulated by a computer. Sometimes abbreviated DAQ or DAS, data acquisition typically involves acquisition of signals and waveforms and processing the signals to obtain desired information....
 despite an often extreme environment. The form factor is often sold by COTS
Commercial off-the-shelf

Commercial, off-the-shelf is a term for Computer software or hardware, generally technology or computer products, that are ready-made and available for sale, lease, or license to the general public....
 vendors, which benefits many consumers who want a customized rugged system, without months of design and paper work.

The PC/104 form factor was originally devised by Ampro Computers in 1987, and later standardized by the PC/104 Consortium in 1992.






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PC/104 (or PC104) is an embedded computer standard
Standardization

Standardization is the process of developing and agreeing upon Standard . A standard is a document that establishes uniform engineering or technical specifications, criteria, methods, processes, or practices....
 controlled by the which defines both a form factor
Form factor

Form factor may refer to:* Form factor or emissivity, the proportion of energy transmitted by that object which can be transferred to another object...
 and computer bus
Computer bus

In computer architecture, a bus is a subsystem that transfers data between computer components inside a computer or between computers. Each bus defines its set of connectors to physically plug devices, cards or cables together....
. PC/104 is intended for specialized embedded computing environments where applications depend on reliable data acquisition
Data acquisition

Data acquisition is the sampling of the real world to generate data that can be manipulated by a computer. Sometimes abbreviated DAQ or DAS, data acquisition typically involves acquisition of signals and waveforms and processing the signals to obtain desired information....
 despite an often extreme environment. The form factor is often sold by COTS
Commercial off-the-shelf

Commercial, off-the-shelf is a term for Computer software or hardware, generally technology or computer products, that are ready-made and available for sale, lease, or license to the general public....
 vendors, which benefits many consumers who want a customized rugged system, without months of design and paper work.

The PC/104 form factor was originally devised by Ampro Computers in 1987, and later standardized by the PC/104 Consortium in 1992. An IEEE standard corresponding to PC/104 was drafted as IEEE P996.1, but never ratified.

Unlike the popular ATX
ATX

The ATX Motherboard form factor was created by Intel in 1995. It was the first big change in computer case and motherboard design in many years....
 form factor which utilizes the PCI
Peripheral Component Interconnect

The PCI Local Bus , or Conventional PCI, is a computer bus for attaching computer hardware in a computer. These devices can take either the form of an integrated circuit fitted onto the motherboard itself, called a planar device in the PCI specification or an expansion card that fits into a socket....
 bus and is currently used for most PC
IBM PC compatible

IBM PC compatible computers are those generally similar to the original IBM Personal Computer, IBM Personal Computer XT, and IBM Personal Computer/AT....
s, the PC/104 form factor has no backplane
Backplane

A backplane is a circuit board that connects several electrical connector in parallel to each other, so that each pin of each connector is linked to the same relative pin of all the other connectors, forming a computer bus....
, and instead allows modules to stack together like building blocks. The stacking of buses is more rugged than typical bus connections in PCs. This is a result of mounting-holes in the corner of each module, which allow the boards to be fastened to each other with standoffs.

The standard size of boards complying to the form factor is 3.55 × 3.775 inches (90.17 × 95.89 mm), while the height is typically constrained to the boundaries of the connectors. A constrained height region is intended to guarantee that modules will not interfere with their neighbors. Vendors often follow these design restrictions to ensure proper stacking of modules, although it is not uncommon to find boards which ignore the form factor requirements.

While a typical system (also referred to as a stack) includes a motherboard
Motherboard

A motherboard is the central printed circuit board in some complex electronic systems, such as modern personal computers. The motherboard is sometimes alternatively known as the mainboard, system board, or, on Apple Inc....
, analog-to-digital converter
Analog-to-digital converter

An analog-to-digital converter is a device which converts continuous signal to Discrete signal digital numbers. The reverse operation is performed by a digital-to-analog converter ....
, and digital I/O
Input/output

In computing, input/output, or I/O, refers to the communication between an information processing system , and the outside world ? possibly a human, or another information processing system....
 (data acquisition
Data acquisition

Data acquisition is the sampling of the real world to generate data that can be manipulated by a computer. Sometimes abbreviated DAQ or DAS, data acquisition typically involves acquisition of signals and waveforms and processing the signals to obtain desired information....
) module, other peripherals are finding their way into the market including GPS
Global Positioning System

The Global Positioning System is a global navigation satellite system developed by the United States Department of Defense and managed by the United States Air Force 50th Space Wing....
 receivers, IEEE 802.11
IEEE 802.11

IEEE 802.11 is a set of standards carrying out Wireless LAN computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are implemented by the Institute of Electrical and Electronics Engineers LAN/MAN Standards Committee ....
 controllers, and USB
Universal Serial Bus

In information technology, Universal Serial Bus is a Serial communications computer bus standard to electrical connector devices to a host computer....
 controllers.

Form factors

Pci 104 Ep405

PC/104

The PC/104 computer bus (first released in 1992) utilizes 104 pins. These pins include all the normal lines used in the ISA
Industry Standard Architecture

Industry Standard Architecture was a computer bus standard for IBM compatible computers....
 bus, with additional ground pins added to ensure bus integrity. Signal timing and voltage
Voltage

Electrical tension is the potential difference between two points of an electrical or electronic circuit, expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor....
 levels are identical to the ISA bus, with lower current requirements.

The pinouts for the PC/104 connector can be obtained here.

PC/104-Plus

The PC/104-Plus form factor adds support for the PCI bus, in addition to the ISA bus of the PC/104 standard. The name is derived from its origin: a PC/104-Plus module has a PC/104 connector (ISA) plus PCI-104 connector (PCI).

PCI-104

The PCI-104 form factor includes the PCI
Peripheral Component Interconnect

The PCI Local Bus , or Conventional PCI, is a computer bus for attaching computer hardware in a computer. These devices can take either the form of an integrated circuit fitted onto the motherboard itself, called a planar device in the PCI specification or an expansion card that fits into a socket....
 connector, but not the ISA connector, in order to increase the available board real estate. The PCI-104 standard is incompatible with PC/104 boards.

The pinouts for the PCI-104 connector are as follows:

PinABCD
1GNDReserved5VAD00
2VI/OAD02AD015V
3AD05GNDAD04AD03
4C/BE0#AD07GNDAD06
5GNDAD09AD08GND
6AD11VI/OAD10M66EN
7AD14AD13GNDAD12
83.3VC/BE1#AD153.3V
9SERR#GNDReservedPAR
10GNDPERR#3.3VReserved
11STOP#3.3VLOCK#GND
123.3VTRDY#GNDDEVSEL#
13FRAME#GNDIRDY#3.3V
14GNDAD163.3VC/BE2#
15AD183.3VAD17GND
16AD21AD20GNDAD19
173.3VAD23AD223.3V
18IDSEL0GNDIDSEL1IDSEL2
19AD24C/BE3#VI/OIDSEL3
20GNDAD26AD25GND
21AD295VAD28AD27
225VAD30GNDAD31
23REQ0#GNDREQ1#VI/O
24GNDREQ2#5VGNT0#
25GNT1#VI/OGNT2#GND
265VCLK0GNDCLK1
27CLK25VCLK3GND
28GNDINTD#5VRST#
2912VINTA#INTB#INTC#
30 -12VREQ3#GNT3#GND


PCI/104-Express

The PCI/104-Express form factor includes the x16 PCI Express (PCIe) bus, and the PCI connector. The 156-pin PCI/104-Express interface can be used with PC/104, EPIC, and EBX form factors.

EBX

EBX (Embedded Board eXpandable
Embedded Board eXpandable

Embedded Board eXpandable is a standardized computer form factor.This format was created for embedded computer systems by a consortium including Motorola and Ampro Computers....
) is a single board computer form factor, 5.75” x 8.00”. The EBX is based on the IEEE-P996 (ISA), PC/104, PC/104-Plus, PCI and PCMCIA. EBX supports PC/104 daughter boards.

EPIC

EPIC
EPIC (form factor)

Embedded Platform for Industrial Computing is a computer form factor standard put forth by a combined effort from WinSystems, VersaLogic, Octagon Systems, Micro/sys, and Ampro Corporations....
 (Embedded Platform for Industrial Computing) is a single board computer form factor which, like EBX, supports PC/104 daughter boards but is smaller than EBX. It allows I/O connections to be implemented as either pin-headers or PC-style ("real world") connectors. The standard provides specific I/O zones to implement functions such as Ethernet, serial ports, digital and analog I/O, video, wireless, and various application-specific interfaces.

EPIC Express

EPIC Express is based on EPIC, but adds the PCI Express
PCI Express

Peripheral Component Interconnect Express , officially abbreviated as PCIe, is a computer expansion card standard designed to replace the older PCI Local Bus, PCI-X, and Accelerated Graphics Port standards....
.

Stacks

A system composed of PC/104, PC/104-Plus, or PCI-104 modules is often referred to as a "stack". Although many stacks include modules which are all the same form factor, it is not uncommon to find PC/104 modules in a stack with PC/104-Plus modules.

Each stack must contain at least one motherboard or CPU
Central processing unit

A central processing unit is an electronic circuit that can execute computer programs. This broad definition can easily be applied to many early computers that existed long before the term "CPU" ever came into widespread usage....
, which acts as a controller for the peripheral components. The motherboard is often referred to as a single board computer (SBC), for it often has interfaces for all standard PC components (i.e. keyboard, mouse, serial ports, etc.). This controller must support the signaling buses used on all add-in modules. It's possible, however, that a peripheral card may perform a stand alone function without requiring a separate motherboard to control it.

There is no strict limit to the number of PC/104 cards which can coexist in one system. However, as more modules are added, the stack height increases, and signaling requirements may not be maintained. A PC/104 stack will usually have a motherboard controller which is also PC/104. Peripheral PC/104 cards can reside on either side of the CPU.

A stack which has any PC/104-Plus modules must be controlled by a PC/104-Plus motherboard controller. Not counting the PC/104-Plus controller, the number of PC/104-Plus peripheral cards in a stack may not exceed four module slices. This is due to the PCI
Peripheral Component Interconnect

The PCI Local Bus , or Conventional PCI, is a computer bus for attaching computer hardware in a computer. These devices can take either the form of an integrated circuit fitted onto the motherboard itself, called a planar device in the PCI specification or an expansion card that fits into a socket....
 specification, which allows four PCI components in a system. (More PCI devices may be added if a bridge device is used.) The same rule applies to PCI-104 stacks.

When the PCI bus connector is used (PC/104-Plus or PCI-104 modules), all peripheral PC/104-Plus modules must connect consecutively on one side of the controller due to the signaling requirements of the PCI bus. Each card with a PCI bus should include a mechanism to assign its position in reference to the controller. Note that this is not required for traditional backplane motherboards, because a card "knows" which slot it is in. A PC/104-Plus or PCI-104 system may also have PC/104 cards, which may be positioned on either side of the CPU farthest away from the PC/104-Plus card(s) (so the PCI bus is not broken).

Popular storage

These small and rugged PC/104 systems often require small non volatile storage devices. Popular storage devices include Compact Flash as well as solid state disk (SSD) devices. These are often more popular than mechanical (rotating) hard drives, which are larger, and are more susceptible to failure in harsh environments. Flash based storage has a more limited amount of writes compared to a mechanical hard drive, but consume less power.

Timeline

Form FactorRelease YearBus Communication
PC/1041992ISA
Industry Standard Architecture

Industry Standard Architecture was a computer bus standard for IBM compatible computers....
 (AT and XT)		2.5
PC/104-Plus1997ISA and PCI2.0
PCI-1042003PCI
Peripheral Component Interconnect

The PCI Local Bus , or Conventional PCI, is a computer bus for attaching computer hardware in a computer. These devices can take either the form of an integrated circuit fitted onto the motherboard itself, called a planar device in the PCI specification or an expansion card that fits into a socket....
1.0
PCI/104-Express2008PCI and PCIe1.0


See also

  • VMEbus
    VMEbus

    VMEbus is a computer bus standard, originally developed for the Motorola 68000 line of Central processing unit, but later widely used for many applications and standardized by the IEC as American National Standards Institute/Institute of Electrical and Electronics Engineers 1014-1987....
  • VPX
    VPX

    VPX, formerly known as VITA 46, is an ANSI standard that provides VMEbus-based systems with support for switched fabrics over a new high speed connector....
  • CompactPCI
    CompactPCI

    A CompactPCI system is a 3rack unit or 6U Eurocard -based industrial computer, where all boards are connected via a passive Peripheral Component Interconnect backplane....


External links