Storage and input methods expand easily and cheaply by plugging in USB 2.1 (or older 1.x) devices.
An (external) USB CD-ROM or CD-RW starts around USD 70~90 and climb fast. Bulk pricing (at OLPC scales) can significantly lower this cost.
CD-ROMs could be used to distribute entire libraries. All you need to run a lending library is a stack of CD-ROMs and one or more USB CD-Readers.
As any USB compliant storage device supported by Linux, should work just fine. In that sense (USB 2.0 standard compliance) also means that any CD-R/W, DVD-R/W (and other letter combinations) should also work.
 Input devices
Most external USB mice, keyboards, and other USB devices will work seamlessly with XO laptops, their availability will be limited in developing countries. See OLPC Human Interface Guidelines/The Sugar Interface/Input Systems to better understand why.
 AD/DA & "Parallel" interfaces
Precisely for these types of ideas the computer needs some sort of basic A/D, D/A and suitably protected bi-directional "parallel" type interfaces. These need to be built-in so their use doesn't add wire spaghetti, cables/conversion boxes don't get lost, is "fumble free" and always available. In short, it must be simple, empowering and an idea generating catalyst. L Pfeffer March 20, 2006
Basic AD/DA can be done on the audio interface which is specifically designed for this purpose. However, for older children, it may be worthwhile for a school to invest in USB devices such as the CREATE USB Interface.
Even more advanced AD/DA can be done using the rest of the sound card channels, as there are multiple left unused on the AD1888 --DyD 14:20, 20 September 2007 (EDT)
 Serial Port
USB-to-serial adapters work well on the OLPC. Currently adapters that are compatible with the pl2032 and ftdi_sio kernel modules are supported.
pl2032 adapters work out of the box right now. some pl2032 adapters:
Dynex (Best Buy private label) DX-UBDB9. Works for me, Rmyers. Aten UC-232A (available at Radio Shack). Iogear GUC-232A (apparently a relabeling of the Aten unit). Any others?
ftdi_sio support apparently has a bug in Linux kernel 2.6.22, which is what the XO currently uses. There is a patch. Has anyone tried to apply it? Does any one have a list of ftdi_sio devices?
At this time, Keyspan adapters do not work. A ticket has been filed for keyspan adapter support (#3050). Keyspan support is, according to this ticket, expected for Update.2, scheduled for 5/30/08.
I know it can be done through USB emulators... but serial ports are simple and easy to use. If someone wants to make some electronic project, or using old hardware (mouse, or serial communications devices), it could be useful to have one.
It is just an idea, but I started making my first hardware projects with this, and even today is cheaper (at least here in Argentina) and easy to make serial ports working hardware (rather than buying PICs and programming them).
And still many hardware has serial ports (networking devices for example).
- Serial ports are NOT robust, at least nine tiny little pins that it's very easy to bend or break, not a good idea. Perhaps with a more robust connector, though IME the parallel port was more useful for electronics projects. 220.127.116.11 16:02, 17 March 2006 (EST)
- The photos from the developer boards show an external RS232 level shifter circuit attached (to some GPIO pins?). Legacy serial/parallel ports are nice for experimenting, there's IMHO no need for this for a laptop which is targeted at 6-12 yo children.
- Not to mention the fact that there IS NO OLD HARDWARE in these 3rd world villages. It would be far better to have an external power plug with circuit breaker switch so that people could use the old bananas they have laying around TO MAKE BATTERIES!!! The kids will be motivated to find a way to pedal less so lets help them learn some science.
 USB vs built-in flash
Question: What's the relative access speed of USB2 thumb drives versus the built-in flash memory?
The cheap solution to adding flash might be an under-lid USB2 port with a cut-out that lets you leave a flash device in-place when the laptop closes. This would not solve the RAM issue (as you don't want to swap to the flash), but it might be the lowest-cost way to give convenient storage expansion.
As the USB flash would be under the lid when the lid was closed, it would need to be in a recess to avoid hitting the screen or bevel. A 9x24x45 (DxWxL) mm recess will hold the popular smaller sticks while a 12x35x70 mm recess should hold even the largest USB sticks. Next to the touchpad, or along the top edge of the keyboard, or under the d-pad & speaker are all good locations.
 USB Hard Drive
In the other hand, as John said, a USB thumb or hard drive, could be easily plugged. These devices currently start around 80 (USD) and 40 Gb. They are not 100% reliable when running of an underpowered USB port or an underpowered USB hub. Some manufactures slow down the drives to make them use less power. No budget USB2 drive could be considered a reliable, rugged, and robust companion to the OLPC PC.
One reason to consider the hard drive option would be to give the device an appropriate device to use for swap space. On the other hand, this may not be possible as the device would not be connected at boot/resume.
Note of course: A hard drive can easily be added by plugging one into USB2 as well. One catch is that rugged, properly cooled USB2 hard drives do not seem to exist at any reasonable price. Another catch is power.
About the power of an external hard drive, I think if someone has money to buy it, it probably has electricity, so it's a matter of designing an external hard drive with with external power (or rechargeable batteries), if not, USB thumbs seems a good option, and they're getting cheaper.
- I understand there are 2.5inch hard disks that take a peak current of 600mA (at 5v) but their average consumption is less than half that. I always though this would be a good spot for a rechargeable battery. 18.104.22.168 16:14, 17 March 2006 (EST)
--Ecologists of Chios, Greece 21:24, 27 July 2006 (EDT)
I thought about an open design for a case for two hard disks, connected together, maybe even through software/hardware RAID, with a battery at the bottom of the case, as well as a socket for a charger. So, you have twin 500GB hard disks connected in RAID to provide 1TB of storage through USB to the laptop, more than enough space for an entire Wikipedia. The battery powers the disks, then when charging is needed it connects to the same charger as the laptop (simultaneously?). And of course design is rugged DIY with easily unscrewed access to the drives.
 Support for external display
It would be nice to have a way to TV-out (RGB + audio), and thus input to an LED projector from a USB port. Clearly, the dual-mode display and the unusual screen dimensions require something to be custom built. If we are all trying to save paper, then it would be great to be able to display work to an audience this way.
 Keyboard Illumination
It is not necessary to illuminate the keyboard if fire is available in the target area. However, if the kids are willing to do the extra pedalling to provide light, there are nice cheap USB-powered LED lights available. This makes a lot more economic sense than burdening every device with illumination by building it into the keyboard.
- Main article: GPS
A GPS unit could be connected either through an RS-232-to-USB or Bluetooth-to-USB adaptor and be used in many contexts. One more reason why USB ports are a VERY good idea.
 Bluetooth adapter
- Main article: Bluetooth
Bluetooth adapters are used to speak to devices using the Bluetooth protocol. This includes mobile phones, GPS units, and external keyboards.
The USB2 interface hardware allows one of the USB ports to be used as a device port as well as a host port. This means that with the proper cable and software, two laptops could be plugged together and you could network them via USB2. They can be daisy-chained in the same way, and should provide ~20 Mbytes/sec of thruput (see GNU Radio USRP software for Linux software that can keep the USB2 bus moving data at maximum speed). There's USB device software in the Sharp Zaurus, which runs Linux and has such a dual-use USB port (USB 1.1 though).
A USB2 cable is much faster than the wireless, and cheaper than adding USB2 ethernet cards + hubs + cables + etc. Running IP, DHCP, and Rendezvous over USB shouldn't be hard; I'm a little surprised it isn't standardized already (like IP over Firewire).
- This is usb-on-the-go and needs the 5-pin tiny connector not the 4-pin normal sized ones because according to the designers it's only useful for PDAs and cameras not real PCs. Scheesh! 22.214.171.124 17:20, 17 March 2006 (EST)
- Also USB has alot of overhad associated with which slows it down and you need the a cable, which is limited to 5m (absolute maximum see if you can find one that longer much less someone in Africa). The wireless appears to have very high range and as it is a/g wireless they should be able to combine the two frequencies for 100Mbit/s which is only 4x slower than usb so not a big deal. Even if you don't use both a and g together and only get 50Mbit/s you can transfer 512Mbytes all the memory on the computer in 73 seconds. Thats plenty fast Lotu
 Cellular Modems
Cellular modems provide Internet data access via cellular phone technology, usually for an extra fee over the standard voice coverage plans. Example data technologies include GSM/GPRS, EDGE, UMTS, EvDO, 1xRTT, CDPD, HSDPA, HSUPA. For setup information see Modem.
 Special Educational devices
It might be worthwhile to develop educational USB devices. One possibility would be a simple A/D converter with some sensors (temp, light, humidity, acceleration, etc). and input conditioning circuits. This would convert the laptop into a measurement device. With some software, it could be used as the basis for numerous science labs. It could also aid in repairing other laptops. Of course, such a device could be used with any USB-equipped computer.
See also OLPC as Datalogger.
 Start collecting USB memory sticks
Smaller USB memory sticks are becoming obsolete as flash memory prices drop. It might make sense to start collecting them for eventual distribution with the laptops. They don't take up much space. They could be useful not just for storage, but also to transport files between schools (see Sneakernet). Sometimes USB memory sticks with FM Radio/MP3 Player are as cheap as one without. Also people may have old low-capacity ones they don't want. They re-charge via the USB port. Children or their families could use them to listen to MP3 audio-books on ear-phones. Also, radio programs could be recorded to the laptop. They may use less power than keeping the laptop on to play MP3s.
 LED panels for light sources
One could build a light source using about 10 white LEDs and have them fixed around a reflector. This could be powered from the USB port. The USB port can safely handle about 650mA of current which should be enough to create a reasonable light source. This would be useful in a lot of places where there is no electricity at all and people have to use oil lamps for light. See http://www.spectrum.ieee.org/dec04/3849 (IEEE Spectrum article) The downside of this is that it would be draining the battery too fast and consequently regular use of this would lead to a shorter battery life, however this can be made an optional peripheral. --Arjunsarwal
 External Storage - A USB Hub for a collection of USB Memory Sticks
If a user had a USB Hub with connectors for say 10 USB Memory Sticks, then they could have several Gigabytes of external storage quite cheaply using old low capacity Memory Sticks that computer-users, manufacturers, wholesalers and retailers don't want anymore. The hub would also be useful for other USB devices.
 USB Bluetooth Adaptors / Dongles for PC-to-Phone file transfer
If a school had a Bluetooth Adaptor, to plug into a USB Port on the Server or one of the XO Laptops, then they could transfer files to/from a Bluetooth Mobile Phone in order to...
a) Distribute eBooks, eBook Reader Programs, other phone software, information files, farm-prices, health leaflets, etc, and other files to phones for use in the wider community.
b) Use Bluetooth phones like Flash Drives, purely as a file-transport medium to other remote places. There, the files could be copied of to another PC, OLPC XO Laptops or Server, or more phones.
c) Copy files to phones, so they become like a mobile 'electronic library' or 'educational tool' with constructionist games.
There is a one-time installation process for the particular make of Bluetooth Dongle, using the supplied CD.
There is also a one time 'pairing' of each new phone and the Server PC (like any 2 Bluetooth Devices). A PIN is entered on both devices. After that, they can communicate any time, but the receiving device must accept the transfer. Bluetooth can also be used for phone-to-phone transfer, allowing phone users to share files even more widely.
Schools may want to use it just for 1-way read-only distribution of files from PC to Phone, to avoid any possibility of viruses or malware. However, there are firewalls and virus checkers for phones I think. The phones are like a small laptop really.
Bluetooth file transfer is fast (3MB per second using V2.0). It avoids messing around with USB Cables and phone-specific software. The dongles cost from $5 or $10 upwards (in 2007) and only one per school is needed. Class 2 dongles reach 10 meters and Class 1 up to 100 meters. In some places, they could be used to create a sort of Bluetooth 'Hotspot', like a WiFi cyber-cafe.
An Infra-Red IRDa Dongle can be used the same way, for Infra-Red phones (often cheaper models than Bluetooth).
A lot of people will have the cheapest phone models, with no Bluetooth or Infra-Red at all, just a USB Slave Port, that a PC USB Host Port can talk to via the phone's supplied USB Cable and a phone manager program like Nokia PC Suite. So, even the cheapest phones could be used to make eBooks, information, games, photos and software available on phones, to the whole village or area.
If 2-way file transfer between School Server PC and Phone was allowed, it could provide the village with a sort of 'email' system. People could read/write text files at home for emails, and link into the school (with internet access) to send/receive the emails to/from friends, relatives and colleagues elsewhere in the world.
Even the school staff or local aid-agencies may find this PC-to-Phone link very useful.
--Ricardo 15:17, 13 December 2007 (EST)
I've successfully hooked a digital camera to my XO. This was a Fuji, others are likely to work. Rmyers 11:11, 15 February 2008 (EST)
 Multicard readers
I've successfully hooked a multi-card reader to my XO. This was a Belkin unit (F5U211ME), others are likely to work. Rmyers 11:11, 15 February 2008 (EST)