bringing my computer into the 21st century

[mark at buttery.org (Mark J. Dulcey)]

Seth Gordon wrote:
> I have a P-II 350 MHz computer sitting in my office, and I want to spiff
> it up, within the limits of my budget, before everything that's
> compatible with its motherboard becomes "legacy hardware".
> 
> In particular, I want to put in a SCSI controller and a few drives, so I
> can set up a RAID system.  However, the prospect of going to
> pricewatch.com and just ordering a few refurbished drives is
> intimidating me, because:
> 
> (a) There appears to be an alphabet soup of competing SCSI versions, and
> I'm not sure in advance what drives are compatible with what
> controllers.
> 
> (b) My motherboard only has a 100 MHz bus, and I don't want to waste
> money on drives that are pumping out data faster than the bus can
> handle.
> 
> What should I be looking for?
> 
> Also, what other CPUs will fit into the same slot as the Pentium II
> (with the same proviso regarding bus speed)?

First, the CPU. You have a Slot 1 motherboard, so you can only put in 
CPUs that match. Slot 1 processors are ancient at this point, so the 
only sources will be liquidation-type dealers; dealers that only sell 
new parts mostly won't have them. Here's a link to one dealer that has them:

http://www.compgeeks.com/products.asp?cat=CPU#Slot%201%20CPU's%20(Celeron/P2/P3)

The fastest processor that would be compatible with your motherboard is 
the 650 MHz/100 MHz bus Pentium III (the very first one in the list), 
though you might prefer to step down a notch of speed and save some 
money. You should also check the web site of your motherboard's 
manufacturer (if they have one) and look up its CPU support; it's 
possible that newer processors won't work, or that you will need to get 
a BIOS update.

An alternative is a "slocket" adapter. That is a little circuit board 
that lets you put a Socket 370 processor in a Slot 1 motherboard. That 
would let you get as high as an 850 MHz processor. pricewatch.com has 
links for the CPUs. But shop carefully - there are reports of various 
compatibility problems with the adapters.

On to the disks...

As for the bus speed issue... the PCI bus runs at 33 MHz, and can 
transfer 32 bits at a time, for a maximum transfer rate of 133 megabytes 
per second. Thus it is theoretically possible for a Ultra160 SCSI card 
to be slowed down by the bus that it is plugged into. However, you would 
need multiple drives to accomplish that trick, since the actual 
sustained data transfer rate of even the very fastest hard disks is 
considerably slower. In reality, UW SCSI will keep up with just about 
any single hard disk; you need more bandwidth only if you have 
concurrent operations on more than one drive.

Here)B?s a summary of the various SCSI speeds (all except the first two 
use synchronous protocols):

Asynchronous: 2.5 MBps
Asynchronous Wide: 5 MBps
Synchronous: 5 MBps
Fast: 10 MBps
Wide: 10 MBps
Fast Wide: 20 MBps
Ultra: 20 MBps
Ultra Wide: 40 MBps
Ultra 2: 40 MBps
Ultra 2 Wide: 80 MBps
Ultra160: 160 MBps (wide only)
Ultra320: 320 MBps (wide only)

The last two are exotic items that you're not likely to find at 
affordable prices, so you can forget about them. And U320 on a PCI bus 
is a complete waste; a U320 controller only makes sense if it's 
integrated into a motherboard (and not through a PCI bridge!), or on 
some special-purpose server bus (or one of the upcoming higher 
performance buses such as PCI-X or HyperTransport) that's faster than PCI.

Don't forget to budget some good cables; my experience with SCSI is that 
the faster speeds (Ultra and up) are quite sensitive, and I recommend 
the fancy twisted-pair cables. (They're required for U160 and U320.) 
They're expensive in stores, but can sometimes be found at reasonable 
prices at the Flea at MIT.

Drives and controllers are, for the most part, downward compatible. But 
there are is a significant exception: differential SCSI, which was a 
high-voltage signaling method made for long cable lengths. Differential 
SCSI drives can only be used with differential SCSI controllers, and 
vice versa. This is not to be confused with low voltage differential 
(LVD) signaling, which is used by the higher SCSI speeds, and which is 
downward-compatible with the plain old single-ended SCSI. Still, to get 
full advantage from the fancy versions of SCSI, you may have to keep 
slower devices off the SCSI chain. Dual-channel controllers are good for 
that purpose.

By the way, for comparison, the IDE speeds:

IDE/ATA/ATA33: 33 MBps
ATA66: 66 MBps
ATA100: 100 MBps
ATA133: 133 MBps

In theory, the two faster versions of ATA should be faster than any SCSI 
connection you're likely to be able to afford. The reality, however, is 
different; a good SCSI drive with a U2W interface will outperform any 
currently available ATA drive, both because the SCSI protocol is more 
efficient, and because the ATA market has concentrated on low cost, low 
performance drives.

For you external fans, FireWire runs at 400 megaBITS/second, which 
(including protocol overhead) is about equivalent to 40 MBps, or the 
equivalent of UW SCSI. The new FireWire 800, found on some new Macs, is 
800 megabits/sec, or about equal to U2W. Most external FireWire boxes, 
however, contain ATA drives and ATA33 to FireWire bridges, so they can't 
reach the theoretical maximum.

The new kid on the block is Serial ATA, which runs at 150 
megabytes/second; in theory, this should be in the same neighborhood as 
U160 SCSI. The Serial ATA disks available so far, however, are 
relatively low performance hardware.

Finally, though... combinations of last year's CPU and motherboard 
technology are quite cheap right now. For example, the Micro Center 
flyer that came in the mail yesterday is offering two CPU+motherboard 
bundles for $130: one with an Athlon XP1800+, and another with a 2.2GHz 
Celeron. Shopping online may yield even better deals; for instance, 
Tiger Direct will give you an XP2200+ bundle for the same $130. So 
before you spend a lot of money improving your old system, you may want 
to consider whether it's time to upgrade it more radically, or build a 
new faster one and retire it to less demanding duties. Of course, you 
will have to buy new DDR RAM for a new motherboard, but it's also cheap 
right now - perhaps even cheaper than RAM for your old motherboard!