Re: High Speed CD-ROM drives

[mjmahon@aol.com (Michael J. Mahon)]

David Empson wrote:

>"Joel" <joelbuckley54.nospam.@hotmail.com> wrote:
>
>> David Empson wrote:
>> > At the very least, you won't get full performance out of a CD-ROM drive
>> > faster than 1x, due to the limited throughput of the Apple II SCSI
>> > cards.  The original SCSI card can't even sustain the throughput
>> > required for 1x, but the high-speed SCSI card might be able to manage 2x
>> > (under GS/OS).
>> 
>> I saw dramatic improvement over the 1X drive.
>> In testing, a CD-600 is 4.5X as fast a CD-150.
>> 
>> These are times for a 65535 block verify under GSOS 6.01
>> This is with DMA.
>> (Speed) Drive  -  DMA Time  - Calc Speed
>> (1X) CD-150  - 362s  - 93kB/s
>> (2X) CD-300  - 103s  - 326kB/s
>> (4X) CD-600  - 80s  -  420kB/s
>> 2GB hard drive 64k block - 120s  - 280kB/s
>
>I'm impressed!  I'd be interested to find out whether a CD-1200 or
>CD-2400 can get a little more speed out of the HS SCSI card.  It can
>theoretically get transfer rates approaching 1 MB per second on a IIgs
>(half that on a IIe), but I don't know whether the GS/OS driver is able
>to sustain that sort of throughput.

Much of the improvement may be due to increased internal buffering
in the CD-ROM drive.  Early drives had little buffering, and once it
was overrun, the drive had to seek and re-sync to resume data
transmission.  A larger buffer means fewer re-syncs.

-michael

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