 The Source for Mac Performance News and Reviews |
|
By Paul J. Tetreault, Jr. 1/30/2000 How to Use
an ATX Case for External Drives or PCI Expansion Chasis |
 |
A Drive Space Solution for the Masses! |
|
|||
|
Want to add some of the tons of neat new storage devices like CD-RWs, Orbs, and SuperDrives to your Mac, no matter what model it is? Have you maxed out your PCI slots and need to add an expansion chasis fom Magma or SBS Bit3? Do you need a box with drive bays, fans, and a power supply for a multi-drive U2W RAID that won't cost more than the drives themselves? The cheapest answer to all of these problems is to buy a big, empty case from the PC world. This article will show you the tricks you need to know to set up and use a PC ATX case and don't be alarmed, you don't have to be a "technical type" to tackle this project. A screwdriver, pliers, wirestrippers with some hook-up wire and about an hour are all it takes. You can use the big case to mount drives on any - or a number of different - types of interfaces. But if you've got a Mac with an internal SCSI bus and limited physical space for drives inside the case - like my 8500 - you can add several new storage devices to your system without wasting a PCI slot for an extra interface card. Mounting your 8500's internal drives in a different case also lightens the load on the power supply if you're planning on adding an interface card that needs power like OrangeMicro's OrangeLink FireWire/USB card. The 8500's internal SCSI bus is a narrow, fast SCSI 2 bus. Narrow means it's 8 bits wide and uses 50 conductor wire and 50 pin connectors, as opposed to wide or ultra wide buses that use 68 conductors. You can still hang 68 pin devices, like the soon to be released Orb SCSI internal drive or a wide hard drive, on the bus with an adapter. You won't realize the full data transfer rate of a wide bus because a fast narrow SCSI 2 bus transfers data at 10 Megabytes per second while a wide (16 bit, 68 conductor) SCSI 2 bus handles up to 20 MBps. But the fast narrow internal bus is still twice as fast as the 5MBps SCSI 1 external bus on most older Macs, making it a much better interface for CDRWs (less chance of buffer underrun when burning a CD due to slow data transfer) or relatively quick removables like the Orb and Jaz. For more on SCSI transfer rates, check out the excellent chart at Trans International. 12 Drive Bays and a 300 Watt Power Supply for $78!The case I chose for this project is the Q500 from In Win, an ATX tower case with 12 drive bays and a 300 watt power supply (for reference, the 8500's PS is 225w). I found the Q500 for only $78.48 from Chase Shop.com, over $100 less than comparable cases from other sources. [Note - the direct product page link no longer worked and after much clicking, I see they no longer list this case model-Mike] For a good deal on the case that's right for you check out "computer components" at CNET Shopper. [Note - be sure to sort C/Net's shopper results by price - as it seems the default to the some other order (like ad payments perhaps?) Check local Computer Shows as well, they might have even lower prices and you could save a *lot* of shipping costs you normally pay from cases sent via mail order.-Mike ;-] PC cases come in two flavors, AT and ATX, depending on the motherboard they are designed to accept. In general, the ATX cases have bigger power supplies and more drive bays. The backplane and power connectors of either style case are not compatible for mounting Mac motherboards - see Dan Calhoun's excellent motherboard transplant article here at XLR8 for how to work around this - but they are perfect for mounting a PCI expansion chasis to give your Mac as many as 7 extra PCI slots. As the pictures show, the Q500 has space for six removable drives on top and six 3.5" drives inside the case. The internal drive bays are in a three-sided metal bracket that can be disconnected from a slide mount on the bottom of the panel that divides the case into top and bottom sections. The only fan provided with the case is internal to the power supply, but there are three fan mounting points, one at the bottom front and two on the back for the upper and lower portions of the case. According to an Apple Til article, the host computer appears both at Bus 0 (the internal bus) ID 0 and Bus 1 (the external bus) ID 0 and 7, giving you a theoretical maximum of 13 (16 minus 3) devices connected to both the internal and external SCSI buses. [Note: On all Macs I've seen, both with onboard scsi and with PCI SCSI Cards, the Controller Chip/Mac motherboard Chip is always ID 7. Boot disks are usually ID 0, with CDRom drives ID 3 in most cases. As long as the drive IDs do not conflict with other devices on the same bus (cable) they can be any available ID number but the controller ID which is usually 7. Many PCI SCSI cards let you change the controller ID, but it's not recommended or needed. See the site's SCSI/IDE/HD topics page for reviews of 4 UW SCSI cards and 3 U2 SCSI cards. The FAQ also has a SCSI/IDE/Controllers topic area as does the Links page.-Mike] But ATTO tools shows the Apple Til may not be correct. According to ATTO tools, the host only appears at ID 7 on both buses. ID 0 is therefore available for connected devices, at least on the internal bus. This means you might be able to connect as many as 14 devices total on both buses. But software drivers for your devices can cause problems, especially if they are old and expect only one SCSI bus. For example, Paperport software version 3.7 checks only the device ID, not the bus as well, so a Paperport scanner will cause ID conflicts with any device with the same ID, even though the other device is on the other bus.
|
|
Extra cooling would be required if you were planning to mount several fast, hot drives like Cheetahs or Atlas 10Ks internally. Fortunately, there is a matrix of cooling holes in front of the 3.5" drive mount that are a perfect spot for mounting internal fans. There is about an inch of clearnance between the metal front of the case where the cooling holes are located and the plastic front case cover, so the plastic cover will not interfere with the fans. If you only want the case to mount extra drives you don't need any other components, but you do need to know how to jumper the ATX power supply so you can switch it on, and we'll show you how to do that on the next page. The ATX power supply normally requires a logic low signal to switch on, which is provided by the PC motherboard from a +5 volt supply the PS delivers as long as it is plugged in. AT power supplies, by contrast, can be connected directly to the power switch on the front of an AT case, so they should not need to be jumpered in order to work. If you want to port your 8500's internal SCSI bus out to the PC case, here are the other components you'll need, where to get them, and what they cost:
YOU HEARD RIGHT! The total cost of this project, including the case and all the SCSI cables and connectors is $222. Be careful though, you could spend hundreds more, especially on "high grade" SCSI components from other suppliers, but the listed parts work great. |
|||
|
|
||
How to Do It!On the next page we'll show you the tricks to jumper the ATX power supply, install the SCSI cable correctly on drives in the external enclosure, and give you a step by step tutorial on how to port your internal SCSI bus out of the 8500's case. |
|||
|
Disclaimer: This article is reader submitted and the site publishers do not guarantee that it's accurate. It is published for reference only - you assume all risk from using this information with your system.
© 2000. All rights reserved. |
|||
