Electronic Design

Time for PC Modularity?

The trend towards standard, hot-swap interfaces like Serial ATA, PCI Express and USB could change the way PCs are built and marketed.

The PC as we know it could be an endangered species. New standards like Serial ATA and PCI Express (PCIe) reveal a PC approach of yore that may dominate yet again. PCs used to be modular since component totals got expensive. While buyers could trade up as new systems became available, many took a more modular approach by adding or replacing components on an as-needed basis. Though connectivity and lack of standards were major hindrances then, fixed PC or semi-custom systems were a partial remedy. Many were mid-tower systems that could take additional peripherals as well as plug replacements for adapter cards (though most users rarely fiddle with these options). Today, a designer can construct a modular system using standard components and get the same performance characteristics that a custom design system could. In fact, modern PCs and laptops have moved to the modular era, albeit in an all-in-one fashion. Top-of-the-line systems have all the features: E-SATA or eSATA (External Serial ATA), external PCI Express, High Speed USB, Gigabit Ethernet and PCMCIA ExpressCard support. The big differences between these standards and those of yesteryear include high speed, hot swapping support, low wire count and robust interconnects. Since they’re standards, 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. 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’s now possible to pop different drives in and out of the same slot. Simple but rugged PCs can be built without the cabling hassles of older PCs. (see Fig. 1) One caveat is still high performance gaming graphics, but this arena tends to make up 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 a basic system design that would incorporate a PC unit using 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,” ED Online 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 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. Otherwise, everything could be 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 that can hide anywhere, even on the back of a monitor. Sounds a bit like a laptop, no? This modular approach tends to turn things around. I would not be surprised to find a processor module powered by the USB hub it controls. USB has already become the main power source for most compact microcontroller development kits I’ve evaluated. High Speed Serial Interfaces USB modularity is great but performance can be even greater with PCI Express and SATA/SAS disk drives. Previously, taking these kinds of interfaces outside the PC’s case was 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. There are a number of options on the PCI Express side. 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, 1Gbit Ethernet and wireless networking will play 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 software that’s fixated on centralized systems. This and DRM (digital rights management) are likely to hold back the modular approach to PCs and media distribution systems that are nothing more than distributed system clusters. So what’s your idea for a great modular base? A motherboard with just RAM, connectors, and a Bluetooth interface? Drop me an email note. Related Links DisplayLink Kensington PCMCIA

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