Rugged systems have been using the PC/104* form factor for two decades. The form factor has remained relevant thanks to updates that have added modern features to the standard. These updates have given developers many variants to choose from, and keeping all the options straight can be a challenge. This blog reviews the many PC/104 variants and related form factors, including EPIC, EBX, and SUMIT.
Here’s a table summarizing all the form factors:
PCB Size (mm)
90 × 96
90 × 96
90 × 96
90 × 96
90 × 96
146 × 203
146 × 203
115 × 165
115 × 165
90 × 96
Let’s start by looking at the PC/104 variants. All of these variants use the same 90 × 96 mm (3.6 × 3.8 inch) form factor, but the connectors and busses available have evolved over the years. Figure 1 illustrates the evolution of the interfaces, starting with the original PC/104 on the left.
Figure 1. The evolution of PC/104.
Here are the essential points about each of these variants:
PC/104 specifies a 104-pin ISA connector. PC/104 is known for its ability to handle extremely harsh conditions, and the form factor has been popular in rugged applications such as military/aerospace and industrial applications.
The PC/104 form factor allows modules to stack together. Each stack must include a CPU module (referred to as either a motherboard or a single-board computer (SBC)). Stacks also include peripheral modules such as analog and digital I/O modules, connectivity modules (such as Wi-Fi* controllers), and storage modules. The modules can be used to create a standalone stack, as illustrated in Figure 2, or with a carrier board as illustrated in Figure 3.
Figure 2. A standalone PC/104 stack. Measurements are in inches.
Figure 3. PC/104 modules stacked on a carrier board.
The PC/104 form factor was originally devised by Ampro in 1987 and standardized by the PC/104 Consortium in 1992. Ampro (which is now part of ADLINK) continues to offer a selection of PC/104 modules, as do several other companies. However, PC/104 mainly exists as a legacy technology, and it is not generally used in new designs.
As illustrated in Figure 4, PC/104-Plus takes the PC/104 form factor and adds a 120-pin PCI* connector. (Hence the name: the form factor is PC/104 plus PCI support.) The legacy connector allows stacks to mix PC/104 and PC/104-Plus modules—a key feature for designers who want to add modern features to legacy PC/104 systems.
Figure 4. The PC/104-Plus form factor. Dimensions are in inches.
PC/104-Plus systems are available from several vendors. One recent example is the ADLINK* CoreModule* 740 SBC. This module includes:
- Intel® Atom™ processor N450 at 1.66 GHz
- Intel® 82801HM I/O Controller with integrated DirectX 9 graphics
- Onboard single channel DDR2 SDRAM
- Single Channel 18-bit LVDS and analog VGA
- Single channel IDE, LPC, floppy, parallel, and serial ports
The PCI-104 form factor includes the 120-pin PCI connector used in the PC/104-Plus, but not the 104-pin ISA connector. Thus, the PCI-104 standard is compatible with PC/104-Plus modules but not with legacy PC/104 modules. The main advantage of the PCI-104 standard is that it frees up board space by eliminating the ISA connecter.
The Aaeon PFM-LNP illustrates the benefits of the extra board space. This module includes a long list of features, including:
- Intel Atom processor N450 at 1.66 GHz
- Intel® 82801HM I/O Controller
- Up to 1 GB of 667 MHz DDR2
- Single channel 18-bit LVDS and analog VGA
- Gigabit Ethernet x 1
- SATA and CompactFlash
- Four USB 2.0, four COM, and four serial ports
- Mini-Card expansion interface
PCI/104-Express takes the PCI-104 form factor and adds a 156-pin PCI Express* (PCIe*) connector. This connector supports four x1 PCIe links and one x16 PCIe link. The 156-pin interface is also used with the EBX and EPIC form factors.
The high-performance PCIe links make PCI/104-Express modules a good choice for applications with high bandwidth needs, particularly those that require advanced graphics. The Lippert Cool XpressRunner-GS45 illustrates the potential of this form factor. It offers:
- Intel® Core™2 Duo at 2.26 GHz
- 1 GB DDR3 RAM (soldered)
- LVDS and VGA graphics
- Gigabit Ethernet port, eight USB 2.0 host, two serial; and two SATA ports
PCIe/104 is PCI/104-Express without the PCI bus. Simple enough!
That’s it for PC/104. Now let’s look at some related form factors:
EBX (Embedded Board eXpandable) specifies a 146 × 203 mm (5.75 × 8 inch) single board computer. It includes ISA and PCA connectors, enabling expansion via PC/104, PC/104-Plus, or PCI-104.
EBX has room for a large amount of I/O and memory. For example, the Diamond Systems Neptune EBX board offers a large selection of analog and digital I/O in addition to the usual lineup of PC-oriented I/O (graphics, Ethernet, serial ports, etc.).
EBX Express is the same as EBX, except that it uses the PCI/104-Express connector (PCI + PCIe). Thus, it can support PC/104-Plus, PCI-104, or PCI/104-Express daughtercards
EPIC (Embedded Platform for Industrial Computing) is a 115 x 165 mm single board computer form factor that is larger than PC/104 but smaller than EBX. Like EBX, EPIC includes ISA and PCA connectors, enabling expansion via PC/104, PC/104-Plus, or PCI-104.
EPIC boards are available with cutting-edge features like the Intel® Core™ i7. For example, the Avalue EPI-QM57 includes:
- Intel® Core™ i7 processor and Intel® QM57 chipset with Intel® AMT 6.0 support
- Up to 4GB DDR3 800/1066 SDRAM
- Dual-monitor, dual-channel LVDS and DVI-I
- RAID 0/1/5/10 support
- Dual Gigabit Ethernet
- One CompactFlash (CF), four SATA, two COM, eight USB, and 16-bit GPIO
- Options including Express Card/34mm and touch screen
EPIC Express is based on EPIC, but uses PCI/104-Express connector (PCI + PCIe).
SUMIT (Stackable Unified Module Interconnect Technology) is a close cousin of PC/104. Like PC/104, SUMIT specifies a connector that allows boards to be connected in stacks. SUMIT connectors support a wide range of serial peripheral interfaces, including USB, SPI, LPC, I²C/SMBus and PCI Express. (See Wikipedia and the SUMIT FAQ for details.)
SUMIT boards are available in several form factors, including the SUMIT-ISM form factor that uses the same 90 mm × 96 mm footprint as PC/104 boards. Although SUMIT-ISM uses the PC/104 form factor, the 52-pin SUMIT connectors are incompatible with PC/104 and its variants. However, SUMIT-ISM boards can include a legacy PC/104 or PCI-104 connector, allowing the technologies to coexist in the same stack. (See Figure 5.)
Figure 5. SUMIT-ISM boards can incorporate PC/104 or PCI-104 connectors.
That’s the end of our review. I hope you found this helpful, and I invite you to submit questions and comments below.
Aaeon and ADLINK are Associate members of the Intel® Embedded Alliance. Avalue and Lippert are Affiliate members of the Alliance. Diamond Systems is a General member of the Alliance.
Roving Reporter (Intel Contractor)
Intel® Embedded Alliance
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