Electronic Design

EiED Online>> Time For PC Modularity?

The PC as we know it could be an endangered species. The migration to laptops is definite and increasing. Couple this with new standards including Serial ATA and PCI Express (PCIe) and it reveals a PC approach of yore that may dominate yet again.

PCs used to be modular because the cost of the components was expensive. Most buyers would simply trade up as new systems became available, but many took a more modular approach by adding or replacing only a component instead of the entire system.

There were significant drawbacks in those days. Connectivity and differences in standards were devastating in general. Distance limitations between devices and a plethora of connector types were enough to keep all but the guru away from all but the simplest enhancements.

The result has been the fixed PC or semi-custom systems. Many were still mid-tower systems that could take additional peripherals as well as plug replacements for adapter cards. Still, most users rarely fiddle with these options.

Another issue is access to certain peripherals like the CD-ROM drive. Placing a unit on the floor keeps it out of the way but makes it hard to access. Likewise, putting the PC on the desktop takes up valuable real estate.

So where am I heading with this diatribe? Why, to the modular PC, of course.

In many ways, today's PCs and laptops have moved to the modular era, albeit in an all-in-one fashion. At this point, only top-of-the-line systems will have all the following features...but they are coming. They include E-SATA or eSATA (External Serial ATA), external PCI Express, High-Speed USB, Gigabit Ethernet and PCMCIA ExpressCard support. The latter combines USB and PCI Express. The big differences between these standards and those of yesteryear include high-speed, hot swapping support, low wire count and robust interconnects. The fact that they are standards is significant as well. It means that third party products should work with each other.

The standards extend to other physical attributes in addition to electrical and, most importantly, the protocol level. The physical attributes show up in things like SATA hard disk drives. Mounting holes and connectors are now in the same location on all drives. The connectors are also designed for hot swapping so it is now possible to pop different drives in and out of the same slot. It allows very simple but rugged PCs to be built without the cabling hassles of older PCs (Fig. 1).

The bottom line is that a designer can now construct a modular system using standard components and get the same performance characteristics that a custom design system could. The one caveat is still high-performance gaming graphics, but this arena tends to be to be a small percentage of the PC world. Likewise, even this type of system could benefit from a modular design with a system that retains card slots for PCI Express graphics boards.

USB Alternatives

In fact, this brings to mind the basic system design that would include a PC unit incorporating only the processor, memory and the video interface. The latter can even be moved out of the base PC unit as well.

DisplayLink's (formally Newnham Research) USB-NIVO may help to eliminate the need for a docking station or video output connector (see "USB Branches Out," EDO #12508). The USB-NIVO is a USB-attached VGA adapter. Its video driver looks like any other video interface to the operating system of a portable device. The difference is that the frame buffer for the driver isn't used to drive the display directly. It is currently incorporated into Kensington's $179 Notebook Expansion Dock (Fig. 2) with Video that also includes 4 USB 2.0 ports, 10/100 Ethernet and audio support.

Other interfaces in the base unit could include eSATA, External PCIe, and Ethernet. USB and External PCIe could be combined in an ExpressCard connection. A video connector is required if the video adapter is integrated in the base unit. Or maybe everything is separate (Fig. 3).

The only other items on the base unit would be a power connection and possibly an on/off or reset switch. This makes the base unit a rather small box and one that can hide anywhere, even on the back of a monitor. If this sounds a lot like a laptop to you, then you are correct.

This modular approach tends to turn things around. I would not be surprised to find a processor module that is powered by the USB hub that it controls. USB has already become the main power source for most compact microcontroller development kits that I have been evaluating.

High Speed Serial Interfaces

USB modularity is great but performance can be even greater with PCI Express and SATA/SAS disk drives. Before, taking these kinds of interfaces outside the PC's case was a hard. The eSATA and SAS external interfaces are already standard. External hard disk SATA drive boxes are now coming out with eSATA, Firewire and USB interfaces.

On the PCI Express side there are a number of options. The PCMCIA ExpressCard combines a 1x PCI Express link with a USB interface. ExpressCards typically use one or the other. ExpressCard interfaces are most often found on laptops, but they will be showing up on desktops as well (Fig. 4).

Standard PCI Express cables and connectors for 4x and 16x are available but these are currently used for linking card cages together. I doubt they will show up much in the PC arena.

On the other hand, 1-Gbit Ethernet and wireless networking will be playing a major part in modularizing systems. Home NAS (network attached storage) units are eliminating the need for more storage directly attached to the motherboard. In fact, the big thing holding back small system clusters of processing, storage and displays is the software that is fixated on centralized systems. This and DRM (digital rights management) are likely to be the main factors in holding back a more modular approach to both computers and media distribution systems that are really nothing more than distributed system clusters.

So what is your idea for a great modular base? A motherboard with just RAM, connectors and a Bluetooth interface? Drop me an email note.

For more information, visit these websites: www.displaylink.com, us.Kensington.com, www.pcmcia.org.

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