jwhitman@st-louis-emh2.army.mil (Jerry Whitman) (02/04/89)
Hi, a couple quick question based on contradictory info seen here. Is the 2090-A SCSI or DMA. If it is SCSI how many devices can it support? What is the make/model of the hard drive in the 2000HD. One article (already deleted) said the 2090-A supported both SCSI and DMA, so what do we really have? Thanks, Jerry
scotty@ziggy.UUCP (Scott Drysdale) (02/05/89)
In article <7941@louie.udel.EDU> jwhitman@st-louis-emh2.army.mil (Jerry Whitman) writes: >Hi, >a couple quick question based on contradictory info seen here. >Is the 2090-A SCSI or DMA. If it is SCSI how many devices can it support? first, DMA (direct memory access) is not exclusively for hard disk controllers. it is a technique where the controller (for whatever, a hard drive in this case) may squirt data directly into memory and notify the CPU when it's done rather than the CPU manually testing for data availability on the controller and manually reading the data from the controller and putting it in memory and counting bytes until it's done. DMA is generally much faster than programmed i/o or interrupt driven i/o, so it's preferred for hard disk controllers and other high volume high speed applications. yes, the 2090A does it's i/o via DMA. SCSI is a standard bus which can handle multiple high speed devices. currently SCSI is used for hard drive and tape controllers, and some people (cltd) are using it for laser printers. another popular way to interface hard drives is the ST506 standard, which is not general purpose by any means but is intended for raw control of a hard drive. ST506 is what most ibm pc's use to connect controllers to hard drives. the 2090A supports both SCSI and ST506 interfaces. >What is the make/model of the hard drive in the 2000HD. ya got me. >One article (already deleted) said the 2090-A supported both SCSI and DMA, >so what do we really have? > >Thanks, Jerry --Scotty
Gap-Dragon@cup.portal.com (John T Manning) (02/06/89)
The hard drive in the 2000HD and 2500 is a 40 meg Rodime unit.