I have an old SCSI drive with a 64 pin connector that I had attached to an SGI machine and I would like to connect it directly to my Linux machine (SuperMicro Server). Is there an adaptor cable that is typically used for this?
You need a SCSI host adapter.
68 pin is/was used with "Wide Ultra SCSI", "Ultra/2 SCSI", etc. up to "Ultra 320" (there is no 64 pin SCSI connector).
For peripherals, SCSI has long-since been replaced by USB.
For high-end HDDs, traditional (Ultra) SCSI has long-since been replaced by SAS (Serial Attached SCSI), and even SATA (in practical use, not as a new generation of SCSI).
While this may make getting an adapter difficult, you might be able to find old SCSI PCI cards on eBay or similar site cheaply, and there are even a few models of PCI Express SCSI adapters floating around.
For example: "Adaptec 2248700-R U320 PCI Express X1 1-Channel SCSI Host Bus Adapter" which is currently listed as 'in stock' for about $77 at Amazon.com.
The remains of Adaptec, which arguably made the most consumer-level SCSI card adapters, are now owned by "Micrsosemi", and while they seem to be the support repository for all things Adaptec storage, they don't seem to produce any SCSI adapters anymore (aside from SATA/SAS adapters).
Similarly, LSI Corp., which probably made the most enterprise-level SCSI adapters, is now owned by "Avago Tech", with a similar story -- only SATA and SAS adapters these days.
Searching around a bit futher, there are a few companies that offered 68-pin SCSI to USB adapters, so that you could utilize your old peripherals via USB once SCSI started dying off; but even those stop-gap adapters seem to have all been discontinued as times changed.