how hard would it be to create a external hard drive enclosure?

It's not difficult, but it has low performance. Using a PC motherboard gives you [perhaps multiple] 100bT or gigabit Ethernet connections, and UDMA66 or faster transfers to/from the hard drive, plus a nontrivial amount of disk cache (main memory in the PC).

On 21 Sep 2003 15:12:36 -0700, snipped-for-privacy@hotmail.com (Michael) wrote in comp.arch.embedded:

Despite another reply that you have gotten, it can be done and done well. Not too long ago I purchased an external drive made by Western Digital for back up. It is a slick plastic enclosure with a 120 GB drive, with both USB 2.0 and firewire interfaces, no Ethernet.

I haven't opened it up to see what kind of processor is inside, but the speed is impressive, not slow at all.

An utterly different, non-comparable scenario. For one thing, the OP is talking about a device that includes Ethernet. That means either he has to write custom software on the PC end, or he has to implement a filesystem and an FTP or SMB (or NFS or ...) sharepoint inside the device. This means that ALL the data, and some interpretive work, has to be funneled through the microcontroller. Further, he's talking about micros that do not have inbuilt hardware support for DMAing to/from IDE and/or 1394/USB interfaces. So even if he just wanted to build a dumb 1394/USB->IDE interface, it would be far slower than the kinds of devices you're talking about.

The AVRs and PICs mentioned are an order of magnitude too slow do do all this bit-banging. Purpose-built interfaces use ASICs. The HDD DMAs into a buffer, the 1394 or USB interface DMAs out of the buffer; the micro issues start and stop commands, basically. This is a totally different scenario from trying to squeeze all the data through a poky 8-bit microcontroller.

To do it properly would be difficult and a lot of work.

Only if there's a requirement that a poky 8-bit microcontroller be used. I've used MIPS chips from Philips that would handle this job easily. (Rummages in drawer and squints to read: PTD1100). You'd need to add external PHY, and a Flash for software; but it'd all fit on a 2" x 3" PCB.

And MIPS would be part of the "PIC or AVR" families since ... when? The OP was specifically asking about these toy projects. Yes, you can do it with a

Hmm. I would have put MIPS in the "various other" catagory. The particular chip I mentioned already has USB and Ethernet MAC, plenty of on-board RAM, particularly nice DMA architecture, and an intelligent external bus interface. (There are also EJTAG and UART I/F to make development easier).

The only aspect that looks difficult is the soldering :-)

Sorry - somehow I missed the "toy" stipulation. I think if I were going to build something like this (even just a one-off for myself), I'd go for all the performance and reliability I could afford...

Yes pics and avrs are the only ucs I mentioned by name - but only because they are the ones that are familiar to me. I'd be open to any suggestions.

So I looked up this chip - and it seemed to be some part of a cable modem (pdf here: